• TABLE OF CONTENTS
HIDE
 Front Cover
 Title Page
 Contributors
 Dedication
 Table of Contents
 Introduction
 Nomenclature and distinguishing...
 Distribution and abundance
 Development of immature stages...
 Larval behavior
 Larval and adult nutrition and...
 Field flight behavior
 Laboratory flight behavior and...
 Blood-feeding behavior
 Sexual behavior and reproducti...
 Control of larvae
 Control of adults
 Acknowledgement
 Back Cover














Group Title: Bulletin University of Florida. Agricultural Experiment Station
Title: Bionomics and physiology of Aedes taeniorhynchus and Aedes sollicitans, the salt marsh mosquitoes of Florida
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
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Permanent Link: http://ufdc.ufl.edu/UF00026782/00001
 Material Information
Title: Bionomics and physiology of Aedes taeniorhynchus and Aedes sollicitans, the salt marsh mosquitoes of Florida
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: iv, 148 p. : ill. ; 23 cm.
Language: English
Creator: Nayar, J. K ( Jai Krishen ), 1933-
Publisher: Agricultural Experiment Stations, Institute of Food and Agricultural Sciences, University of Florida
Florida Agricultural Experiment Stations, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville
Publication Date: 1985
Copyright Date: 1985
 Subjects
Subject: Mosquitoes -- Physiology -- Florida   ( lcsh )
Mosquitoes -- Ecology -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references.
Statement of Responsibility: editor, J.K. Nayar.
General Note: "August 1985."
 Record Information
Bibliographic ID: UF00026782
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltuf - ADA7417
oclc - 14348675
alephbibnum - 000579571
issn - 0096-607X ;

Table of Contents
    Front Cover
        Front Cover
    Title Page
        Page i
    Contributors
        Page ii
    Dedication
        Page iii
    Table of Contents
        Page iv
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
    Nomenclature and distinguishing characteristics
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
    Distribution and abundance
        Page 14
        Page 15
        Page 16
        Page 17
    Development of immature stages and larval excretion
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
        Page 40
        Page 41
        Page 42
    Larval behavior
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
    Larval and adult nutrition and adult excretion
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
        Page 55
        Page 56
        Page 57
        Page 58
        Page 59
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
    Field flight behavior
        Page 67
        Page 68
        Page 69
        Page 70
        Page 71
        Page 72
        Page 73
        Page 74
        Page 75
        Page 76
        Page 77
        Page 78
        Page 79
        Page 80
        Page 81
        Page 82
        Page 83
        Page 84
        Page 85
        Page 86
        Page 87
        Page 88
    Laboratory flight behavior and energetics
        Page 89
        Page 90
        Page 91
        Page 92
        Page 93
        Page 94
    Blood-feeding behavior
        Page 95
        Page 96
        Page 97
        Page 98
        Page 99
        Page 100
        Page 101
        Page 102
        Page 103
    Sexual behavior and reproduction
        Page 104
        Page 105
        Page 106
        Page 107
        Page 108
        Page 109
        Page 110
        Page 111
        Page 112
        Page 113
        Page 114
        Page 115
        Page 116
        Page 117
        Page 118
        Page 119
        Page 120
        Page 121
        Page 122
        Page 123
    Control of larvae
        Page 124
        Page 125
        Page 126
        Page 127
        Page 128
        Page 129
        Page 130
        Page 131
        Page 132
        Page 133
        Page 134
        Page 135
        Page 136
        Page 137
        Page 138
    Control of adults
        Page 139
        Page 140
        Page 141
        Page 142
        Page 143
        Page 144
        Page 145
        Page 146
        Page 147
    Acknowledgement
        Page 148
    Back Cover
        Page 149
Full Text



August 1985


Bionomics and Physiology of
Aedes taeniorhynchus and Aedes sollicitans,
The Salt Marsh Mosquitoes of Florida


J.K. Nayar, editor




















Agricultural Experiment Stations
Institute of Food and Agricultural Sciences
University of Florida, Gainesville


Bulletin 852









BIONOMICS AND PHYSIOLOGY OF AEDES TAENIORHYNCHUS AND
AEDES SOLLICITANS, THE SALT MARSH MOSQUITOES OF FLORIDA



















EDITOR: J. K. Nayar



























Florida Agricultural Experiment Stations
Institute of Food and Agricultural Sciences
University of Florida, Gainesville






CONTRIBUTORS


Beidler, E. J., Director, Indian River Mosquito Control,
Vero Beach, Florida

Bidlingmayer, W. L., Professor, Florida Medical Entomology
Laboratory, IFAS, University of Florida, Vero Beach,
Florida

Dodd, G. D., Assistant Director, Indian River Mosquito
Control, Vero Beach, Florida

Edman, J. D., Professor, Department of Entomology, University
of Massachusetts, Amherst, Massachusetts

Haeger, J. S., Entomologist, Retired from Florida Medical
Entomology Laboratory, IFAS, University of Florida,
Vero Beach, Florida

Linley, J. R., Professor, Florida Medical Entomology
Laboratory, IFAS, University of Florida,
Vero Beach, Florida

Nayar, J. K., Professor, Florida Medical Entomology
Laboratory, IFAS, University of Florida,
Vero Beach, Florida

Nielsen, E. T., Sherwood Hammock Biological Laboratory, Rt. 4,
Box 69, Ft. Pierce, Florida

O'Meara, G. F., Professor, Florida Medical Entomology
Laboratory, IFAS, University of Florida,
Vero Beach, Florida

Sauerman, D. M., Jr., Assistant Professor, Florida Medical
Entomology Laboratory, IFAS, University of Florida,
Vero Beach, Florida

Rathburn, C. B., Jr., Entomologist, West Florida Arthropod
Research Laboratory, Panama City, Florida

Van Handel, E., Professor, Florida Medical Entomology
Laboratory, IFAS, University of Florida,
Vero Beach, Florida


ii

























This bulletin is dedicated to
the memory of

Maurice W. Provost, Ph.D.
1914-1977



A scientist and scholar whose contributions in basic mosquito
research and wildlife conservation made him a giant in the
field. His influence through his guidance of the Florida
Medical Entomology Laboratory and through his writings has
profoundly improved the stature of the science of mosquito
research, and of wildlife conservation.


iii









Chapter


Chapter



Chapter


Chapter



Chapter


Chapter


1.


2.




3.


4.



5.


6.


Chapter 7.



Chapter 8.


Chapter


Chapter


Chapter


9.


10.


11.


Chapter 12.


CONTENTS

Introduction ...................... 1
J. K. Nayar

Nomenclature and Distinguishing
Characteristics ................... 5
J. K. Nayar

Distribution and Abundance.......... 14
W. L. Bidlingmayer and J. S. Haeger

Development of Immature Stages
and Larval Excretion .............. 18
J. K. Nayar

Larval Behavior.................... 43
J. R. Linley

Larval and Adult Nutrition and
Adult Excretion ................... 50
J. K. Nayar and E. Van Handel

Field Flight Behavior.............. 67
E. T. Nielsen, J. S. Haeger, and
W. L. Bidlingmayer

Laboratory Flight Behavior and
Energetics ........................ 89
J. K. Nayar and D. M. Sauerman, Jr.

Blood Feeding Behavior............. 95
J. D. Edman

Sexual Behavior and Reproduction... 104
G. F. O'Meara and J. S. Haeger

Control of Larvae.................. 124
E. J. Beidler and G. D. Dodd

Control of Adults.................. 139
C. B. Rathburn, Jr.


Acknowledgments ................................ 148


iv






CHAPTER 1


INTRODUCTION

J. K. Nayar

The two most important and dominant salt marsh mosquitoes
found along the more than 2000-km coastline of Florida are the
black salt marsh mosquito, Aedes taeniorhynchus (Wiedemann),
and the eastern salt marsh mosquito, Aedes sollicitans
(Walker). Both species belong in the tribe Aedini of the
subfamily Culicinae in the family Culicidae, and the dipteran
suborder Nematocera. Aedes sollicitans is a more northern
species than Ae. taeniorhynchus, but the area of overlap in
their range extends fully 1600 km (1000 miles) both north and
south of Florida (Provost 1951). From light trap data,
Provost (1951) showed that the latitude of equal numbers for
the two species bisects Florida from the mouth of the St.
John's River on the east coast to the mouth of the Suwannee
River on the west coast.

Historically, both salt marsh species have been the most
important pests of human and livestock in coastal Florida from
early spring through fall. Both species are diurnal biters,
Ae. sollicitans being aggressive in sunlight while Ae.
taeniorhynchus bites more exclusively in shade or at night
(Provost 1951). These mosquitoes have been the reason for the
establishment of mosquito control in Florida; there are 50
mosquito control districts with combined budgets in excess of
26 million dollars in 1981-82 (Breeland & Mulrennan 1983). At
least half or more of these resources are directed at
controlling these two salt marsh species. However, in spite
of control efforts, these two species continue to be major
pests.

In addition to being serious pests in Florida, both
species are natural and potential vectors of important
arthropod-borne viruses and parasites that attack human and
other vertebrates. Both Ae. taeniorhynchus and Ae. sollici-
tans are important vectors of the epidemic form of Venezuelan
Equine Encephalitis (VEE) virus (Sellers et al. 1965, Sudia
1972), several strains of Eastern Equine Encephalitis (EEE)
virus (Causey et al. 1962, Chamberlain et al. 1966, Crans et
al. 1977), and Cache Valley virus (Buescher et al. 1970, Yuill
and Thompson 1970). Two strains of Ae. taeniorhynchus have
been shown to be potential vectors of St. Louis Encephalitis
(SLE) virus (Chamberlain et al. 1966). Several strains of
Kauri (Anderson et al. 1960, Aitken et al. 1964), Gumbo Limbo
(Theiler and Downs 1973), Keystone, Trivittatus and Tensaw
(Wellings et al. 1972) viruses have been isolated from field
collected Ae. taeniorhynchus, in Florida and in the Caribbean
Islands.


1






Wuchereria bancrofti, a filarial parasite of humans, has
been found in nature in Ae. taeniorhynchus populations in St.
Croix, West Indies (Craig and Faust 1970). In Florida, Ae.
taeniorhynchus may also serve as a vector, as it supports
development of W. bancrofti in the laboratory after in vitro
feeding on infected blood from volunteer Haitian refugees
(Yangco et al. 1984).

Both Ae. taeniorhynchus and Ae. sollicitans have been
shown to be potential and natural vectors of Dirofilaria
immitis, etiologic agent of dog heartworm and human pulmonary
dirofilariasis in Florida (Ludlam et al. 1970, Nayar and
Sauerman 1975, Sauerman and Nayar 1983), and of Dirofilaria
tenuis, a parasite of raccoons in Florida (Pistey 1958).

This ability of both species to act as vectors of viruses
and parasites suggests that these mosquitoes have the poten-
tial to pose a health hazard, in addition to their role as
serious pests of human and other vertebrates in coastal
Florida.

During the past three decades, salt marsh Aedes have been
studied extensively in the laboratory and field at the Florida
Medical Entomology Laboratory (FMEL), Vero Beach, Florida, the
West Florida Arthropod Research Laboratory, Panama City,
Florida, and at several mosquito control districts. Many of
the laboratory studies became possible after Ae. taenio-
rhynchus had been successfully colonized (Haeger 1958), even
though attempts to colonize Ae. sollicitans have been
unsuccessful. It is useful to put information gathered over
the last 30 years in perspective for the planning of future
research on these and other salt marsh species. The purpose
of this bulletin, therefore, is to provide an organized source
of information on these mosquito species, for use by both
public health entomologists and mosquito control personnel.


2






REFERENCES CITED


Aitken, T. H. G., L. Spence, and R. Manuel.
1964. Virus transmission studies with Trinidadian
mosquitoes. IV. Kairi virus. J. Med. Ent. 1:
50-52.
Anderson, C. R., T. H. G. Aitken, L. P. Spence, and
W. G. Downs.
1960. Kairi virus, a new virus from Trinidadian forest
mosquitoes. Am. J. Trop. Med. Hyg. 9: 70-72.
Breeland, S. G., and J. A. Mulrennan, Jr.
1983. Florida mosquito control. Pest control 51:
18,20,22-24.
Buescher, E. L., R. J. Byrne, C. G. Clarke, D. J. Gould, P. K.
Russell, F. G. Schneider, and T. M. Yuill.
1970. Cache valley virus in the Del Mar Va. Peninsula.
1. Virologic and serologic evidence of
infection. Am. J. Trop. Med. Hyg. 19: 493-502.
Causey, 0. P., R. E. Shope, and H. W. Laemmert.
1962. Report of an epizootic of encephalomyelitis virus
in Para, Brazil. Revta Serv. esp. Saude publ.
12: 47-50.
Chamberlain, R. W., R. H. Gogel, and W. D. Sudia.
1966. Experimental vector studies with strains of St.
Louis encephalitis virus isolated from mosquitoes
during the 1964 epidemics. J. Med. Ent. 3: 268-
270.
Craig, C. F., and E. C. Faust.
1970. Clinical Parasitology. 8th Edition, Lea &
Febiger, Philadelphia.
Crans, W. J., J. D. Downing, and A. A. Di Edwardo.
1977. The vector surveillance program in 1976. Proc.
N.J. Mosq. Control Assoc. 64: 59-62.
Haeger, J. S.
1958. The colonization of Aedes teniorhynchus Wied.
(Diptera, Culicidae). Proc. N.J. Mosq. Exterm.
Assoc. 45: 80-88.
Ludlam, K W., L. A. Jachowski, and G. F. Otto.
1970. Potential vectors of Dirofilaria immitis. J. Am.
Vet. Med. Assoc. 157: 1354-1359.
Nayar, J. K., and D. M. Sauerman, Jr.
1975. Physiological basis of host susceptibility of
Florida mosquitoes to Dirofilaria immitis. J.
Insect Physiol. 21: 1965-1975.
Pistey, W. R.
1958. Studies on the development of Dirofilaria
tenuis. Chandler 1942. J. Parasit. 44: 613-626.
Provost, M. W.
1951. The occurrence of salt marsh mosquitoes in the
interior of Florida. Fla. Ent. 34: 48-53.


3





Sauerman, D. M., Jr., and J. K. Nayar.
1983. A survey for natural potential vectors of
Dirofilaria immitis in Vero Beach, Florida.
Mosquito News 43: 222-225.
Sellers, R. F., G. H. Bergold, 0. M. Suarez, and A. Morales.
1965. Investigations during Venezuelan equine
encephalitis outbreaks in Venezuela 1962-1964.
Am. J. Trop. Med. Hyg. 14: 460-469.
Sudia, W. D.
1972. Arthropod vectors of epidemic Venezuelan equine
encephalitis. In Venezuelan Encephalitis. Pan.
Am. Hlth Org. Sci. Pub. No. 243, pp. 157-161.
Washington, D.C. Sept. 1971.
Theiler, M., and W. G. Downs.
1973. The arthropod-borne viruses of vertebrates. An
account of the Rockefeller Foundation Virus
Program. 1951-1970. Yale University Press, New
Haven. 578 pp.
Wellings, F. M., A. W. Lewis, and L. V. Pierce.
1972. Agents encountered during arboviral ecological
studies. Tampa Bay Area, Florida, 1963 to 1970.
Am. J. Trop. Med. Hyg. 21: 201-213.
Yangco, B., A. L. Vincent, A. C. Vickery, J. K. Nayar, and
D. M. Sauerman, Jr.
1984. An epidemiological survey of filariasis among
refugees in south Florida. Am. J. Trop. Med.
Hyg. 33: 246-251.
Yuill, T. M., and P. H. Thompson.
1970. Cache Valley virus in the Del Mar Peninsula.
IV. Biological transmission of the virus by Aedes
sollicitans and Aedes taeniorhynchus. Am. J.
Trop. Med. Hyg. 19: 513-519.


4






CHAPTER 2


NOMENCLATURE AND DISTINGUISHING CHARACTERISTICS

J. K. Nayar

NOMENCLATURE

Binomial taxa and synonyms

Aedes taeniorhynchus (Wiedemann). (See Belkin et al. 1970;
Knight and Stone 1977).

Culex taeniorhynchus Wiedemann 1821. Type-loc: Mexico
(NMW) (9); Belkin 1968; Howard, Dyar and Knab 1917 (d, 9,
L, E); Gerry 1932 (9); Gjullin 1937 (9); Darsie 1951
(P); Lane 1953 (d, 9, L); Bohart 1954 (L); Carpenter and
LaCasse 1955 (d, 9, L); Forattini 1958 (P); Belkin et al.
1970 (d, 9, P, L).
Culex damnosus Say 1823. Type-loc: Pennsylvania,
United States (NE), Coquillett 1906.
Taeniorhynchus niger Giles 1904. Type-loc: Antigua
Island [Lesser Antilles] (BM). Belkin 1968 (lectotype
design).
Culex portoricensis Ludlow 1905. Type-loc: San Juan,
Puerto Rico (USNM).
Aedes epinolus Dyar and Knab 1914. Type-loc:
Ventanillas, Peru (USNM).
Aedes (Ochlerotatus) taeniorhynchus of Edwards 1932; King
et al. 1944; Matheson 1944; Carpenter and Chamberlain
1946; Lane 1953; Carpenter and LaCasse 1955; Horsfall
1955; Perez-Vigueras 1956; Stone et al. 1959; Forattini
1965; Montchadsky and Garcia Avila 1966; Porter 1967;
Page 1967.
Aedes (Taeniorhynchus) taeniorhynchus of Dyar 1928.
Aedes taeniorhynchus of Matheson 1929; Hill and Hill
1945; Hill 1948; Thompson 1947.
Ochlerotatus taeniorhynchus of Coquillett 1906.
Culicelsa taeniorhynchus of Felt 1904; Theobald 1907.
Culex taeniorhynchus of Theobald 1901, 1903, 1905a, 1910.
Aedes (Taeniorhynchus) portoricensis of Dyar 1922.
Aedes niger of Howard et al. 1917; Johnson 1919; Gowdey
1926.

Aedes sollicitans (Walker). (Belkin et al. 1970; Knight
and Stone 1977).
Culex sollicitans Walker, 1856. Type: lectotype female,
Charleston, South Carolina.


5






Aedes (Ochlerotatus) sollicitans of Edwards 1932; King et
al. 1944; Matheson 1944; Carpenter and Chamberlain 1946;
Lane 1953; Carpenter and LaCasse 1955; Horsfall 1955;
Perez-Vigueres 1956; Stone et al. 1959; Forattini 1965;
Montchadsky and Garcia 1966; Porter 1967; Page 1967.
Aedes (Taeniorhynchus) sollicitans of Dyar 1922, 1928.
Aedes sollicitans of Howard et al. 1917; Johnson 1919;
Gowdey 1926; Hill and Hill 1945; Thompson 1947.
Ochlerotatus sollicitans of Coquillett 1906.
Grabhamia sollicitans of Theobald 1903, 1905a, 1905b,
1907.
Culex sollicitans of Theobald 1901; Felt 1904.

Unless indicated by area or name, binomial taxa Ae.
taeniorhynchus and Ae. sollicitans are implied in this
bulletin.

DISTINGUISHING CHARACTERISTICS

Aedes mosquitoes, like all other mosquito species,
develop through four stages -- egg, larva, pupa, and adult.

Distinguishing characteristics of different stages of Ae.
taeniorhynchus and Ae. sollicitans have been described in
detail by Belkin et al. (1970), Carpenter and LaCasse (1955),
and King et al. (1960). The salient characteristics of each
stage are as follows.

EGG

Aedes taeniorhynchus and Ae. sollicitans eggs are laid
singly and are described by Craig and Horsfall (1960) as
follows.

Aedes taeniorhynchus

Shape: Variable, elongate obovoid to broadly fusiform;
ventral side broadly crescentic, dorsal side nearly straight;
greatest diameter extending from midsection to anterior third.
Size: Length 641m 804 p, mean 746 * 7m ; dorsoventral
diameter 205 g 264p mean 235p 15p. Color: With
exochorion intact, grayish cast; with exochorion removed,
black and variably shiny. Exochorion: Distinct, flaky,
readily removed. Chorion by reflected light: Reticulation
obscure or of low relief, linear in the long axis of the
egg. Chorion by transmitted light: All cells at least three
times as long as width at middle; cells roundly polygonal with
caudal and occasionally lateral bud-like arms; caudal arms
elongate, up to one-half as long as entire cell; boundaries of
contiguous cells generally appearing as irregular, punctate or


6






chain-like walls; surface of cells divided into irregular
sections or discs.

Aedes sollicitans

Aedes sollicitans eggs are very similar to those of Ae.
taeniorhynchus with respect to shape, size, and color, with
the following exception: the cells of the chorion of Ae.
sollicitans are broader in relation to length and have lateral
arms.

LARVAL INS TARS

There are four larval instars in each species. Only the
fourth larval instar is described here.

FOURTH INSTAR LARVA (Cf. Belkin et al. 1970, Carpenter and
LaCasse 1955).

Aedes taeniorhynchus

Head capsule: Unevenly darkly pigmented, darkened on
collar. Antenna: Less than half as long as the head,
sparsely speculate; antennal tuft: small, double or triple,
inserted slightly before middle of shaft, not reaching tip.
Head hairs: postclypeal (4) small, branched; upper frontal
(5) and lower frontal (6) long, single preantennal (7) short,
multiple, barbed. Prothoracic hairs: 1 medium, single; 2
short, single; 3 short, usually double; 4 short, single; 5
long, usually single; 6 long, single; 7 long, usually double.
Body speculate. Lateral abdominal hair: 6 usually double on
segments I and II, with three or more branches on III-V,
single on VI. Comb: of eighth segment with about 9 to 20
scales in a patch; individual scales small, rounded apically,
and fringed with subequal spinules. Siphonal index: usually
a little less than 2.0; pecten: of about 11 to 17 short,
evenly spaced teeth reaching middle of siphon or slightly
beyond; siphonal tuft: multiple, barbed, inserted beyond
pecten, not more than half as long as basal diameter of the
siphon; dorsal preapical spine: as long as the apical pecten
tooth. Anal segment: ringed by the saddle, saddle speculate
posteriorly; lateral hair: single, shorter, than the saddle;
dorsal brush: bilaterally consisting of a long lower caudal
hair and a shorter multiple upper caudal tuft; ventral brush:
large, confined to the barred area; gills: usually much
shorter than the saddle, bluntly rounded.

Aedes sollicitans

Chaetotaxy and general morphology essentially as in Ae.
taeniorhynchus, differing in following conspicuous features.


7






Head capsule: with more conspicuous ocular bulge. Antenna:
darkened from near base; spicules stronger and more numerous.
Lateral abdominal hairs: 6-III-V usually double. Comb:
scales with distinct differentiated median apical spinule.
Siphon: distinctly more slender and lighter in color; pecten
usually more extensive, usually with more than 17 teeth,
occasionally 1 or 2 apical teeth slightly detached. Anal
saddle: without distinct spicules dorsolaterally near caudal
margin. Gills: somewhat longer but not exceeding dorsal
saddle length.

PUPA (cf. Belkin et al. 1970)

Aedes taeniorhynchus

Cephalothorax: moderately to darkly pigmented, lighter
ventrally. Hair 1-C usually double; 3-C usually triple; 8-C
at least triple. Trumpet: uniformly darkly pigmented,
contrasting; short; pinna large. Metanotum and Abdomen:
lightly to moderately pigmented; darker anteriorly. Hair 10-C
multiple, long; 11-C, double or with strong barbs. Hair 1-II
large, with dendritic branching, 1-III usually with 6-8
barbed branches, 1-IV-VII single or double; 5-IV-VI usually
double, sometimes triple; 6-III-VI usually single; 9-VII
usually with at least 5 barbed branches. Paddle: uniformly
lightly pigmented except for darkened mid-rib and external
buttress. Terminal Segments: female genital lobe with long
projecting cercus.

Aedes sollicitans

Chaetotaxy in general is similar to Ae. taeniorhynchus,
differing in following conspicuous features. Cephalothoracic
hairs: 4-7-C with more branches. Trumpet: narrower, with
smaller pinna. Metanotum and anterior abdominal segments:
unevenly pigmented; most hairs with pigment rings around
alveoli. Hair: 1-II smaller and with fewer branches, 1-III
with more branches; 5-III shorter and with more branches; 6-
II-VI usually at least double.

ADULT FEMALE (cf. Carpenter and LaCasse 1955)

Aedes taeniorhynchus

Medium sized to rather small black species, which shows
variations in color from north to south Florida. Head:
proboscis dark-scaled, with a white ring near middle; palpi
short, dark, with white scales at tips. Occiput with a median
patch of golden-yellow to pale golden-brown lanceolate scales,
bounded on either side by a large patch of broad, appressed,
white scales enclosing a small dark-scaled area; erect forked
scales on central part pale. Tori brown, with white scales on


8






inner surface. Thorax: integument of scutum dark brown;
scutum clothed with narrow golden-brown scales becoming pale
yellow to nearly silver-white on the anterior margin, the
prescutellar space, and immediately above the wing bases.
Posterior pronotum with narrow dark-brown scales. Scutellum
with yellowish to silver-white scales and brown setae on the
lobes. Pleura with small patches of broad, flat, grayish-
white scales. Scales on sternopleuron extending about halfway
to anterior angle (often with scattered scales to near angle),
separate from patch on prealar area. Mesepimeron with a patch
of scales on upper half, lower half bare. Hypostigial spot of
scales absent. Lower mesepimeral bristles none or one.
Abdomen: first tergite with a median patch of dark scales, a
few white scales often intermixed; remaining tergites dark-
scaled, with narrow basal white bands dorsally and conspicuous
white patches laterally; apices of the distal segments with a
few pale scales. Sternites white-scaled basally, dark-scaled
or speckled with white apically. Legs: Femora and tibiae
dark-scaled, pale on posterior surface; knee spots white.
Hind tarsi dark, segments 1 to 4 each with a broad, basal,
white ring, segment 5 usually entirely white; front and
middle tarsi dark, with narrower basal white rings on segments
1 to 3, segments 4 and 5 with rings reduced or absent. Wing:
Length about 2.8 to 3.2 mm. Scales narrow, dark.

Aedes sollicitans

A medium-sized brown species with banded proboscis,
speckled wings, and conspicuously ringed tarsi. Differing
from Ae. taeniorhynchus in the following conspicuous features.
Head: proboscis dark-scaled, ringed with white near middle;
palpi short, dark, with a few white scales at tips. Occiput
with a broad median patch of narrow golden-yellow scales,
bounded on either side with a submedian patch of narrow, dark,
bronze-brown scales, with broad, appressed, yellowish scales
surrounding a patch of dark scales laterally; erect forked
scales on central part of occiput pale, those on lateral
region dark. Tori brown, with pale scales on inner and dorsal
surfaces. Thorax: integument of scutum black; scutum with
narrow, golden to golden-brown scales dorsally, becoming dark
bronze-brown laterally; anterior margin and prescutellar space
with somewhat paler scales; often a pair of narrow, rather
indefinite, submedian lines of pale-yellow to golden-yellow
scales extending nearly the full length of the scutum.
Posterior pronotum with narrow, curved, bronze-brown scales,
grayish white on ventral part. Scutellum with light-golden
scales and darker setae on the lobes. Pleura with dense,
poorly defined patches of appressed grayish-white scales.
Scales on sternopleuron extending to anterior angle, not
distinctly separate from patch on prealar area. Mesepimeron
bare on lower one-third to one-half. Hypostigial spot of few


9






to many scales. Lower mesepimeral bristles none to one.
Abdomen: first tergite with a median patch of yellowish-
white scales; remaining tergites dark, each white laterally,
pale yellow basally and medially. Venter whitish to pale-
yellow-scaled, speckled with dark scales. Legs: femora and
tibiae dark, liberally speckled with pale scales, posterior
surface pale, knee spots white. Hind tarsus with segment 1
ringed with white at base and with a yellow ring at middle,
segments 2 to 4 with broad, white, basal rings, segment 5
entirely white; front and middle tarsi similarly marked, but
with bands narrower on segments 1 to 3, absent from 4; segment
5 of front tarsus varies from entirely dark to nearly all
white; segment 5 of middle tarsus mostly white, blended with
dark scales. Wing: length about 3.5 to 4.5 mm. Scales
broad, mixed brown and white.

ADULT MALE (cf. Carpenter and LaCasse 1955)

Aedes taeniorhynchus

Coloration similar to that of the female. Terminalia:
Lobes of ninth tergite about as broad as long, each with three
to five stout setae. Tenth sternite sclerotized apically.
Phallosome stout, cylindrical, rounded apically, open
ventrally, closed dorsally. Claspette: stem slender, pilose,
reaching a little beyond apex of basal lobe, bearing a short
seta before apex; claspette filament nearly as long as the
stem, curved, tapered to point, and bearing a prominent
simple sharp retrorse projection medially on the convex side.
Basistyle: about three and a half times as long as mid-width,
clothed with large scales and numerous long and short setae;
basal lobe broadly rounded, bearing many slender setae on
apex; apical lobe absent. Dististyle: about half as long as
the basistyle, broadened medially, pilose; claw slender, a
little more than one-fourth as long as the dististyle.

Aedes sollicitans

Coloration similar to that of the female. Terminalia:
lobes of ninth tergite short, wider than long, each bearing
four to seven short spines. Tenth sternite heavily
sclerotized. Phallosome stoutly conical, about two-thirds as
broad as long, open ventrally, closed dorsally, rounded at
apex. Claspette stem rather stout, pilose, extending to or
slightly beyond basal lobe, bearing a short seta near apex
arising from a prominent tubercle; claspette filament as long
as the stem, slender, curved. Basistyle: about three times
as long as mid-width, clothed with scales and numerous long
and short setae; basal lobe only slightly raised, bearing
numerous short setae; apical lobe absent. Dististyle: about
two-thirds as long as the basistyle, broader at basal third,
pilose; claw slender, one-fifth as long as the dististyle.


10






REFERENCES CITED
Belkin, J. N.
1968. Mosquito studies (Diptera: Culicidae). IX. The
type specimens of New World mosquitoes in European
museums. Contr. Am. Ent. Inst. 3: 1-69.
Belkin, J. N., S. J. Heinemann, and W. A. Page.
1970. Mosquito studies (Diptera, Culicidae).
XXI. The Culicidae of Jamaica. Contr. Am. Ent.
Inst. 6: 1-458, illus.
Bohart, R. M.
1954. Identification of first stage larvae of California
Aedes (Diptera, Culicidae). Ann. Ent. Soc. Am.
47: 355-366, illus.
Carpenter, S. J., and R. W. Chamberlain.
1946. Mosquito Collections at Army Installations in the
Fourth Service Command. 1943. J. Econ. Ent 39:
82-88.
Carpenter, S. J., and W. J. LaCasse.
1955. Mosquitoes of North America (north of Mexico).
Univ. Calif. Press, Berkeley. vi + 360 pp.,
illus, 127 pits.
Coquillett, D. W.
1906. A classification of the mosquitoes of North and
Middle America. U.S. Bur. Ent. Tech. Ser.
11: 31 pp.
Craig, G. B., Jr., and W. R. Horsfall.
1960. Eggs of floodwater mosquitoes. VII. Species of
Aedes common in the southeastern United States
(Diptera: Culicide). Ann. Ent. Soc. Am.
53: 11-18, illus.
Darsie, R. F., Jr.
1951. Pupae of the culicine mosquitoes of the
northeastern United States (Diptera, Culicidae,
Culicine). Cornell Agri. Exp. Stat. Memoir
No. 304. 67 pp., illus.
Dyar, H. G.


Dyar,


Edwar


1922. The mosquitoes of the United States. Proc. U.S.
Nat. Mus. 62: 1-119.
1928. The mosquitoes of the Americas. Carnegie Inst.
Wash. Publ. No. 387. Washington, D.C. 616 pp.
H. G. and F. Knab.
1914. New mosquitoes from Peru (Diptera, Culicide).
Insecutor Inscit. Menstr. 2: 58-62.
ds, F. W.
1932. Diptera, Fam. Culicidae. In Genera insectorum, P.
Wytsmann, ed., Fas. 194, V. Verteneuil and L.
Desmet, Brussels. 258 pp.


Felt, E. P.
1904.


Mosquitoes or Culicidae of New York State. N.Y.
State Misc. Bull. 79: 241-246.


11






Forat


tini, 0. P.
1958. "Culicidae" que se crianm em buracos da
carangueijos (Diptera). Revta Brasil Biol.
18: 175-179, illus.
1965. Entomologia medical. Culicini: Culex, Aedes e
Psorophora. Vol. 2 Univ. Sao Paulo 506 pp.


Gerry, B. I.
1932. Morphological studies of the female genitalia of
Cuban mosquitoes. Ann. Ent. Soc. Am. 25: 31-75,
illus.
Giles, G. M.
1904. Notes on some collections of mosquitoes received
from abroad. J. Trop. Med. 7: 381-384.


Gjullin, C.
1937.


M.
The female genitalia of the Aedes mosquitoes of
the Pacific Coast States. Proc. Ent. Soc. Wash.
39: 252-266, illus.


Gowdey, C. C.
1926. Catalogus Insectorum Jamaicensis. Jamaica Dept.
Agr. Ent. Bull. 4: 114 pp.
Hill, R. B.


1948. The mosquitoes of Jamaica. Inst. Jamaica Bull.
Sci. Ser. 4. 60 pp.
Hill, R. B., and C. McD. Hill.
1945. Catalogus Insectorum Jamaicensis. Supplement.
list of mosquitoes found in Jamaica. Jamaica
Dept. Agr. 3 pp.
Horsfall, W. R.


A


1955. Mosquitoes their bionomics and relation to
disease. Ronald Press Co., New York. 723 pp.
Howard, L. 0., H. G. Dyar, and F. Knab.
1917. The mosquitoes of North and Central America and
the West Indies Systematic description, part II.
Wash. Carnegie Institute Washington (Publ. No.
159) Vol. 4, pp 525-1064, Washington, D.C.
Johnson, C. W.
1919. A revised list of the Diptera of Jamaica. Am.
Mus. Nat. Hist. Bull. 41: 421-449.
King, W. V., G. H. Bradley, and T. E. McNeel.
1944. The Mosquitoes of the Southeastern States (rev.
ed.). U.S. Dept. Agr., Misc. Pub. 336: 1-96.
King, W. V., G. H Bradley, C. N. Smith, and W. C. McDuffie.
1960. A handbook of the mosquitoes of the Southern
United States. Agr. Handbook 173, U.S. Dept of
Agriculture. 188 pp.
Knight, K. L., and A. Stone.
1977. A catalog of the mosquitoes of the World (Diptera:
Culicidae). Ent. Soc. Am., College Park, Md.
611 pp.
Lane, J.
1953. Neotropical Culicidae. Vol. I and II. Univ. of
Sao Paulo, Brazil. 1112 pp., illus.


12






Ludlow, C. S.
1905. Mosquito notes. No. 4 Can. Ent. 37: 385-388.
Matheson, R.
1929. A Handbook of the mosquitoes of North America.
C. C. Thomas, Springfield, Ill. 268 pp.
1944. A Handbook of the mosquitoes of North America.
Comstock Publ. Assoc., N.Y. 314 pp.
Montchadsky, A. S., and I. Garcia Avila.
1966. Las larvas de los mosquitos (Diptera: Culicidae)
de Cuba, Su biologia Y determination. Poeyana
(A) 28: 1-92.
Page, W. A.
1967. Observations on man-biting mosquitoes in Jamaica.
Proc. R. Ent. Soc., London (A) 42: 180-186.
Perez-Vigueras, I.
1956. Los Ixodidos y culicidos de Cuba. Su historic
natural y medical. Habana 579 pp.
Porter, J. E.
1967. A check list of the mosquitoes of the Greater
Antilles and the Bahamas and Virgin Islands.
Mosquito News 27: 35-41.
Say, Thomas.
1923. Description of dipterous insects of the United
States. J. Acad. Nat. Sci. (Philadelphia)
3: 9-54.
Stone, A., K. L. Knight, and Helle Starcke.
1959. A synoptic catalog of the mosquitoes of the world
(Diptera: Culicidae). Vol. 6. The Thomas Say
Foundation, Ent. Soc. Am. 358 pp.
Theobald, F. V.
1901. A monograph of the Culicidae or mosquitoes,
Vol. I. Brit Mus. Nat. Hist., London. 424 pp.
1903. A monograph of the Culicidae or mosquitoes,
Vol. 3. Brit. Mus. Nat. Hist., London. 359 pp.
1905a. The mosquitoes or Culicidae of Jamaica.
Institute of Jamaica, Kingston, Jamaica. 40 pp.
1905b. Diptera. Family Culicidae. Genera Insectorum
26: 50 pp.


1907. A monograph of
Vol. 4. Brit.
1910. A monograph of
Vol. 5. Brit.


the Culicidae or mosquitoes,
Mus. Nat. Hist., London. 639 pp.
the Culicide or mosquitoes,
Mus. Nat. Hist., London. 646 pp.


Thompson, G. A.
1947. A list of the mosquitoes of Jamaica, British West
Indies. Mosquito News 7: 78-80.
Walker, F.
1856. Insecta Saundersiana, Vol. I. Van Voorst,
London. p. 415-474.
Wiedemann, C. R. G.
1821. Diptera exotica. Edition 1, Pt. II, pp. i-iv +
43-50. Kiliae. (Also published in enlarged
edition, 1821.)


13






Chapter 3


DISTRIBUTION AND ABUNDANCE

W. L. Bidlingmayer and J. S. Haeger

Aedes taeniorhynchus and Aedes sollicitans are produced
in the salt marshes of all coastal counties of Florida.
Aedes taeniorhynchus clearly predominates in peninsular
Florida while Ae. sollicitans is proportionately more common
to the north (Provost 1949), even though larger New Jersey
light trap collections of the latter species have been taken
in peninsular Florida (Provost 1951a). In areas where the
numbers of either species are normally small, it is charac-
teristic of both species for numbers to erupt occasionally.
The adults of Ae. taeniorhynchus are a problem only within
about four miles of the coast (Provost 1951b) and Ae.
sollicitans for even a lesser distance (Crans 1977), as it
occurs most commonly on the barrier islands (Provost
1951a). In Indian River County, barrier island populations
of Ae. sollicitans were twice as great as 6 miles to the west
(Bidlingmayer 1974). However, both species do occur in small
numbers in the interior of the state. As the numbers of Ae.
taeniorhynchus in the interior decreased from south to north,
reflecting the south-north decline of coastal populations,
the origin of interior specimens was probably the coastal
marshes (Provost 1951b). In Florida, known occurrences of
breeding in the interior counties by Ae. taeniorhynchus
(Provost 1951b) or by Ae. sollicitans (George Alexander,
personal communication) are rare although in the coastal
counties the larvae of both species are commonly found in
freshwaters as well as saltwater (Provost 1951b).

In southern Florida Ae. taeniorhynchus may occur at any
time water covers the breeding areas but, due to annual rain-
fall and tidal patterns, numbers are much greater during
summer and autumn. In the south, Ae. sollicitans occurs
mostly during the cooler months (Provost 1949), although
population outbreaks may occur even in summer (Provost
1951a). The eggs of Ae. taeniorhynchus require higher water
temperatures for hatching than those of Ae. sollicitans
(Bidlingmayer 1956), and thus in north Florida large numbers
occur only in summer and early fall, whereas Ae. sollicitans
is more abundant in spring and fall (Provost 1949).

Since larvae have been found in water with salinities
ranging from fresh to greater than seawater (Provost 1953),
the concentration of these mosquitoes near the coast seems to
be due to the requirements of the adult (Provost 1951b). The
salt marshes of Florida may be classified into three types
(Provost 1968, 1973): (1) North of St. Augustine on the
East Coast and of Tampa on the West Coast the marshes are


14






lposaed Of grasses, principally cordrasst
fl-ora), black rush ( re e r a s s m o a
_I~ ~patens) c saltr erlanus r altern-

herbaceous/woody r transtlot ma I la ta) (F
glasswort rSa e P aeenn'als saltwort--1"0ae mnated 5l the
cordgrass, a ) l ata n ia s gt s
mpsand blacker amounts of
avenn a(3) South of Palm Beach and Nmpl (Avice
w dominated b red ( hlPes are m

a(Aviennia nit id mangroves ih -4g9 nd black
g naturally Eac t -of mars h l
g marsh and at the mean high tide mar sh usinto
low natural a OV marsh-tth e O mark (MuW s ay
Stamps a lare The rof iles o often indicated by a
low natural levee The profiles of the scrub and mangrove
swamps are similar although the extent of low marsh in
nrovr swamps can be extensive. In the gra loy arshs
(supp ng a growths e
proportion of hgh mars (supPorting a growth of salt meadow





SLOW MARSH MH^^
SPaludal basin

MOSTLY CORDGRASS (Sartina a ternifora) SALT MEA
OGTEN BLACK R (g./ (Juncus roemeriana ) SPIKE GRAss (DistICh sDcata)

GRASS SALT MARSH ETC sDiata)







RED MANGROVE SRhizoPhora -a
NGROV ANGROVE (Az --
SLAC MANGROVE Aicennia nitida)
GLASSWORTS (Satis maritima)
(Salicornia spj.)

MANGROVE SWAMP ETC



ra 3.1. Intertidal profiles in Florida with plant
water mLW, ea low and high marsh. M da, ith plants
ow water (modified fa mean high
ro1 Provost 19735

15






grass, saltgrass, and occasionally black rush) is usually
small compared with the amount of low marsh (cordgrass, black
rush). In scrub and mangrove marshes the proportion of high
marsh saltwortt, glasswort, black mangrove) is greater than
the amount of low marsh (red mangrove). The high marsh is
dry much of the year, whereas most of the low marsh is
alternately flooded and exposed daily by the tides (Provost
1977a). Since mosquito larvae must have water for 4 to 10
days to complete larval development, only high marsh can
produce mosquitoes (Provost 1977b).

Eggs are never laid in low marsh (Provost 1977b), and
apparently, gravid females seem able to determine which marsh
areas drain rapidly after flooding and which do not.
Oviposition occurs in high marsh areas from which water is
lost principally by evapotranspiration. Gravid females of
Ae. sollicitans select open grassy sites for oviposition
whereas Ae. taeniorhynchus females utilize both grassy and
wooded sites. The greatest numbers of eggs are deposited
about midway between the highest and lowest water levels.
The females avoid the areas flooded only at maximum pool
elevations and also avoid the bare exposed bottoms of
depressions. The eggs are usually inserted singly into the
interstices of the organic detritus and leaf litter on the
ground. Eggs may also be placed in small crevices on the
clumps of grasses, on rough stems of other salt marsh plants,
and in soil fissures created by drying hydraulic fills.
Although egg densities are highly variable, soil samples
containing as many as 1,000 to 10,000 eggs per square foot
(Provost 1957, 1969) have been found. The eggs of both
species can survive months of exposure to environmental
conditions with little loss of viability (Bidlingmayer 1956,
Provost 1960, 1969). Because fully embryonated eggs hatch
within minutes after flooding, the adult emergence is often
highly synchronous, resulting in mass emergences over a 2 or
3 day period (Provost 1952).

It is not by chance that the earliest, and even today
most, mosquito control districts are located along the
Atlantic and Gulf coasts. Provost (1948) states, "It is
primarily their [salt marsh mosquito] invasions that spurred
into existence the mosquito control districts now established
in the state." All coastal areas have histories of mosquito
hordes and these may be verified in the Everglades National
Park today. In 1951 Provost reported that for Ae. taenio-
rhynchus there were records of 60 New Jersey light trap
collections of over 10,000 females per night (58 in Florida,
2 in Delaware) and 4 such collections of Ae. sollicitans (3
in Delaware, 1 in New Jersey) (Provost 1951a). The largest
collections were 265,216 Ae. taeniorhynchus from Sanibel
Island, Florida, and 64,028 Ae. sollicitans from Delaware.


16






REFERENCES CITED
Bidlingmayer, W. L.
1956. Studies on the viability of salt-marsh mosquito
eggs. Mosquito News 16: 298-301.
1974. The influence of environmental factors and
physiological stage on flight patterns of
mosquitoes taken in the vehicle aspirator and
truck, suction, bait and New Jersey light traps.
J. Med. Ent. 11: 119-146.
Crans, W. J.
1977. A summation of studies pertaining to the
migratory behavior of Aedes sollicitans and their
potential value to mosquito control. Proc. 64th
Ann. Mtg. N.J. Mosq. Control Assoc. pp. 56-58.
Provost, M. W.
1948. Mosquito control in the state of Florida.
Fla. Hlth Notes 40: 93-109.
1949. Mosquito control and mosquito problems in
Florida. Proc. 17th Ann. Mtg. Calif. Mosq.
Control Assoc. pp. 32-35.
1951a. Relative numbers of Aedes taeniorhynchus and
Aedes sollicitans in Florida during recent years.
Proc. 22nd Ann. Mtg. Fla. Anti-Mosquito Assoc.
12 pp.
1951b The occurrence of salt marsh mosquitoes in the
interior of Florida. Fla. Ent. 34: 38-53.
1952. The dispersal of Aedes taeniorhynchus. I.
Preliminary studies. Mosquito News 12: 174-190.
1953. The water table on Sanibel Island. Unpublished.
29 pp. + maps.
1957. The dispersal of Aedes taeniorhynchus II. The
second experiment. Mosquito News 17: 233-247.
1960. The dispersal of Aedes taeniorhynchus. III.
Study methods for migratory exodus. Mosquito
News 20: 148-161.
1968. Managing impounded salt marsh for mosquito
control and estuarine resource conservation.
Pp. 162-171 in LSU Marsh and Estuary Symposium,
1967.
1969. Ecological control of salt marsh mosquitoes with
side benefits to birds. Proc. Tall Timbers
Conference on Ecological Animal Control by
Habitat Management. pp. 193-206.
1973. Mean high water mark and use of tidelands in
Florida. Fla. Sci. 36: 50-66.
1977a. Source reduction in salt-marsh mosquito control:
past and future. Mosquito News 37: 689-698.
1977b. Mosquito Control. Pp 666-671 in Coastal
Ecosystem Management: A Technical Manual for the
Conservation of Coastal Zone Resources. John R.
Clark, ed., (The Conservation Foundation). John
Wiley & Sons, N.Y. 928 pp.


17






CHAPTER 4


DEVELOPMENT OF IMMATURE STAGES AND LARVAL EXCRETION

J. K. Nayar

Aedes mosquitoes have four stages -- egg, larva, pupa and
adult. Development of each of the four stages in Ae. taenio-
rhynchus and Ae. sollicitans takes about the same duration and
is as follows.

EGG

In Florida, eggs of Ae. taeniorhynchus and Ae.
sollicitans may be collected from sod during all months of the
year. More eggs are collected during dry periods than during
the rainy seasons, because during rainy seasons most of the
eggs hatch in response to frequent flooding. In one study, 30
cm square sod samples collected at monthly intervals from
swales at the FMEL field plots yielded several thousand eggs
in each sample, except during April, when the yield was very
low, because most hatched a week earlier due to rainfall.
Eggs collected at different times during the year hatched
readily when conditioned at 270C and 70% to 80% relative
humidity for 2 to 3 days. Thus, in Florida, eggs of these
species do not undergo a true diapause during dry or cold
seasons (Anderson 1970).

EMBRYOGENESIS AND EGG-HATCHING

Embryogenesis of Ae. taeniorhynchus and Ae. sollicitans
begins as soon as eggs are laid, but completion of embryonic
development takes place only if there is enough moisture
(70% to 80% RH) and temperatures are between 200C and 320C
(Nayar 1967b). The duration of embryonic development varies
from 3 to 4 days at 270C to 300C to 8 to 10 days at 200C to
220C. Eggs become dormant at the completion of embryogenesis,
but when submerged in deoxygenated water the eggs hatch
synchronously within 15 minutes to an hour. Fully embryonated
eggs can be stored at temperatures between 80C and 300C and at
70% to 80% RH for various lengths of time depending on the
temperature, e.g., about 4 to 6 months at 8 C and 1 to 2
months at 300C. However, if eggs stored at temperatures lower
than 200C and under dry conditions (30% to 40% RH) are
subjected to the hatching procedure, they hatch erratically,
unless they are preconditioned for a day or two at 250C to
270C (Moore and Bickley 1966). Newly laid eggs from Ae.
taeniorhynchus laboratory colonies, held for 3 to 7 days under
different light conditions such as DD (continuous darkness),
LL (continuous light) or LD 12:12 (alternating light and dark
periods) and at temperatures between 240C and 350C and 70% to
80% RH, hatched synchronously when submerged in deoxygenated


18






water (Nayar 1967b). Different light conditions therefore do
not affect either the development of the embryo or the hatch-
ing of the eggs. The major factors controlling the embryo-
genesis and the conditioning of eggs prior to application of
the hatching stimuli are temperature and humidity.

In the laboratory, a hatching stimulus is provided by
deoxygenation of the water, achieved either by replacement of
oxygen from water by bubbling nitrogen or carbon dioxide
(Horsfall et al. 1958), or by removal of oxygen on addition of
Fleischmann's dry active yeast (Nayar 1967b, Nayar and
Sauerman 1970). Further details on the eggs of aedine
mosquitoes are given in Clements (1963) and Horsfall et al.
(1973).

In the field, eggs of Ae. taeniorhynchus and Ae.
sollicitans become dormant after embryogenesis, but during
warm weather hatching occurs when the marshes are covered by
rainwater or monthly or seasonal high tides. Enormous numbers
of larvae may be produced in a single brood (Provost 1952,
King et al. 1960). Dormant eggs can withstand long periods of
drying, and the percentage of hatching at each flooding is
variable.

In certain cases, eclosion from the eggs may be
inhibited. O'Meara (1975) has shown that inhibition could be
due to the interactions between maternal and embryonic
factors. A lethal trait is associated with the bleached-eye
(bl) mutant of Ae. taeniorhynchus whereby fully formed bl
embryos fail to hatch. However, reduced hatchability occurs
in bl mosquitoes only when the maternal parent possesses the
bl/bl genotype. The bl embryo from heterozygous (bl/+)
females and normal (+) embryos from bl females are not
affected. Nearly all eggs laid by bl females are rescued by
bl/+ bearing sperm. The sex of the offspring does not
influence hatchability.

LARVAL DEVELOPMENT

Aedes taeniorhynchus and Ae. sollicitans pass through
four larval instars. The effects of five environmental
factors (temperature, light regime, diet, water salinity, and
larval density) on larval and pupal development in the
laboratory are described by Nayar (1967a,b) Nayar and Sauerman
(1970a), and Provost and Lum (1967). These results are
summarized as follows. Each of the first three larval instars
reared from simultaneously hatched eggs exhibit synchronized
larval molting peaks in each instar at any constant tempera-
ture between 220C to 34C, under all light regimes (DD, LL and
LD 12:12) and on quantities of food above a certain minimum
(Fig. 4.1). The duration of the first three larval stadia is
about a day for each instar at 270C; it is slightly shorter at


19






at higher temperatures and considerably longer at lower
temperatures. The duration is slightly longer when larvae are
over-crowded in the pan, or when larvae are reared in water of
salinity higher than 50% seawater rather than in 25% seawater
or below. The duration of the fourth stadium is also
controlled by the five environmental factors previously
mentioned. The duration of the fourth larval stage can be
best described when the following three points in development
are used: the time of onset of the fourth instar, the time of
onset of the pupal stage, and the complete disappearance of
fourth instar larvae from the culture (Fig. 4.1). From the
first two points, the minimum duration of the fourth stadium
can be determined, and from the first and third point the
total duration of the fourth stage can be calculated.




LARVAL MOLTING PEAKS UNDER DO

Is 2nd J'd 4th or PUPAL








MINIMUM MEAN DURATION OF PUPATION
DURATION OF LARVAL INSTAR
.................. ......... I INS TAR
------------ iZSTisR
-' 3rd INSTAR PRESENT IN CULTURE
-41 wrSTAR
MEAN OF MOLTING PEAK ONSET ED ---4Ih INTAR
PUPATION





Fig. 4.1. Diagrammatic presentation of the terms used to
describe larval and pupal development and rate of growth
in cultures of Aedes taeniorhynchus (from Nayar 1967b).

Larvae reared under different combinations of at least
two of the five environmental factors showed that the minimum
duration of the fourth larval stage is 2 days at 280C. It is
shortened at high temperatures or low salinities (<25% sea-
water as the rearing medium) and prolonged at low temperatures
or high salinities (>50% seawater). The duration is slightly
longer under LL than under DD or LD 12:12. The maximum
duration of the fourth stage is prolonged on a low diet and
shortened on a high diet. A low diet combined with high
rearing medium salinities (>50% seawater) has an additive
effect in prolonging the duration of the fourth-larval stage.


20






PUPAL DEVELOPMENT AND PATTERN OF PUPATION

The effect of environmental factors on the duration of
the pupal stage can be considered also by using three
reference points: the onset of pupation, the onset of adult
emergence, and the eclosion of all pupae. The onset of
pupation is dependent mainly on temperature, as under standard
rearing conditions with 75 larvae reared on basic ration in
10% seawater at 27C, onset occurs at 105 hr in Ae. taenio-
rhynchus and at 98 hr in Ae. sollicitans from simultaneously
hatched eggs. The onset of pupal ecdysis is delayed at lower
temperatures, and advanced at higher temperatures. Sub-
standard larval rearing conditions, such as low ration, high
salinities (25% or more seawater), or overcrowding (more than
150 larvae per 20 x 30 mm pan), delay the onset of pupal
ecdysis and lengthen the duration of the pupal stage.
Continuous light (LL) delays the onset and lengthens the
duration of the pupal stage only slightly.

The pattern of pupation has been studied extensively in
Ae. taeniorhynchus and is affected by all five previously
listed environmental factors, but more so by the light regime
and temperature variations than the other three factors.

5- A

I0-

0-

W I I I I I I I I I I I I I I I






20-

10-
I0.



20-
F
20--

96 120 4 1 19
HOURS AFTER HATCH

Fig. 4.2. Sequence of pupation in Aedes taeniorhynchus
reared in groups of 300 larvae at 27TT in 10% seawater
under different light regimes on (a) basic ration -- A, C,
and E, and (b) 4 X basic ration -- B, D, and F. Ordinate:
2-hour running average of number of pupae per hour (from
Nayar 1967b).


21






Effect of light regimes on endogenous circadian rhythm of
pupation

In continuous darkness (DD), the endogenous pattern of
pupation is cyclic or rhythmic, forming a sine wave, with an
average period of 21.5 hr between the means of the peaks at
270C and standard rearing conditions (Fig. 4.2A) (Nayar
1967a,b). This rhythm disappears in LL (Fig. 4.2C) or with an
excess of food (Fig. 4.2B, 4.2D). However, when a light
regime of LD 12:12 is imposed, the endogenous pupation peaks
become very distinct with period means between peaks of 22.3
hr at 270C (Fig. 4.2E, 4.2F). Pupation also occurs in peaks
in Ae. sollicitans with period means between peaks of 23.12 hr
at 27"C (Nayar and Sauerman 1970).

The effects of light pulses and light cycles on the
endogenous circadian rhythm of pupation in Ae. taeniorhynchus
are described by Nayar (1968). The salient features are as
follows. A sinusoidal pattern of pupation, which is evident
only under continuous darkness, was the result of a simulta-
neous hatching of the eggs. A single light pulse synchronized
each peak of pupation and established a new phase for the
pupation rhythm. If the single light pulse lasted four or
more hours, it was effective in phase-establishment as early
as immediately after egg hatching and as late as 72 hr after
hatch. The amount of phase-shift was proportional to the
duration of the light stimulus, the greatest phase-shift
resulting from the longest signal. Giving a light pulse dur-
ing different phases of the light-dark (LD) cycles, showed
that sensitivity to light stimuli was greater during the first
12 hr than during the second 12 hr of the LD cycle. The
phase-response curve obtained for the pupation rhythm under
standardized rearing conditions was similar to those reported
for different single animals and populations. The persistence
of the pupation rhythm under constant conditions of light and
temperature following alternating conditions, the distinct
displaying of phase-shift, transients, and phase resetting,
substantiate that the pupation rhythm is an endogenous diurnal
rhythm. Light-dark cycles of less than 24 hr, varying from 12
to 22 hr, imposed during earlier stages of development, did
entrain the pupation rhythm, although the LD cycles were not
learned. This diurnal rhythm of pupation, while not suitable
for the study of either time measurement or the general
properties of circadian clocks, is suitable for studying the
physio-ecological processes in this insect.

Effect of temperature on endogenous circadian rhythm of
pupation

Water temperature is one of the important factors
affecting the duration of development and in controlling the
time of the day when peaks of pupation occur. The effect of

22






temperature on the pattern of pupation in Ae. taeniorhynchus
was studied by rearing larvae under standard conditions of
LD 12:12 at unit increments from 220C to 340C, the water
temperatures that occur in the field during the main breeding
season in Florida (Provost 1974). Although separate experi-
ments were conducted with sunrise, noon, sunset, and midnight
hatching of eggs, the results presented here are combined as
if egg hatching was random throughout the day. The main
pupation peak at 290C (Fig. 4.3) illustrates how the circadian

A







C9
'I .

/




/ .,/ '\'

." /.







i,'


0600 0900 1200 1500 1800 2100 2400 0300 0600
TIME OF DAY

Fig. 4.3. Synchronization of pupation peak in Aedes taenio-
rhynchus at 290C under LD 12:12, by sex and hatching time.
A, males (...), females (----) and both sexes combined
T----) with hatch times at 0600, 1200, 1800 and 2400.
B, Male and C, Female hatches at 6 hours apart. Hatch
times 0600 --), 1200 (--), 1800 (-..-) and 2400 (..).

rhythm of pupation minimized the differences due to egg
hatching times, e.g., a spread of 18 hr (0600 to 2400) in
hatching times has a spread of only 2.5 hr in mean pupation
time. The time of day when egg hatching occurs is a factor in
timing of the pupal ecdysis (Provost and Lum 1967) because the
onset of pupation fell just at the time of the light to dark
change at that temperature, resulting in a small "advance
peak", which is also influenced by the endogenous rhythm. The


23








Table 4.1. Number and percentage (in brackets) of males and females


in individual daily
to 340C.


peaks of pupation from larvae reared


of Aedes taeniorhynchus
at temperatures from 22uC


PUPATION PEAKS

Temperature Sex Advanced 1st 2nd 3rd 4th 5th


22"C

23C

240C

250C

260C

270C

280C

290C

30C

310C


d
9
d
9
d
9
d
9
d
9
d
9
d
9
d
9

9

9


23
2
56
3
71
7
46
2
47
13
9
1
19
2
3
0
27
5
5
0


251
62
316
141
397
148
332
146
355
197
422
234
417
158
363
161
379
228
394
161


168
150
124
129
129
235
120
175
129
225
151
252
156
255
165
272
116
227
174
223


78
157
70
156
28
143
50
186
31
118
29
84
25
140
27
167
24
136
31
161


29
153
46
129
2
40
20
111
2
16
5
14
4
39
8
38
0
14
7
22


7
38
11
34
0
0
0
9






Table 4.1 (continued)


320C

330C

340C


d
9


d
9


16
2
6
0
15
2


1 4 It


328
121
300
94
279
109


197
181
218
229
188
160


22uC-25uC d 196 (93.3) 1296 (72.3) 541 (44.0) 226 (26.0) 97 (18.3) 18 (18.2)
9 14 ( 6.7) 497 (27.7) 689 (56.0) 642 (74.0) 433 (81.7) 81 (81.8)

26uC-30uC d 105 (83.3) 1936 (66.4) 717 (36.8) 136 (17.4) 19 (23.6)
9 21 (16.7) 978 (33.6) 1231 (63.2) 645 (82.6) 121 (80.4)

31uC-34uC d 42 (91.3) 1301 (72.8) 777 (49.5) 186 (18.7) 26 (11.5)
9 4 ( 8.7) 485 (27.2) 793 (50.5) 810 (81.3) 200 (88.5)

TOTAL d 343 (89.8) 4533 (69.8) 2035 (42.9) 548 (20.7) 142 (15.9) 18 (18.2)
9 39 (10.2) 1960 (30.2) 2713 (57.1) 2097 (79.3) 754 (84.1) 81 (81.8)


tm


53
225
40
197
62
227


3
65
9
54
7
59






second, or main, peak reveals the true mean time of pupation
at these temperatures. Male Ae. taeniorhynchus develop faster
than females and pupate earlier (Table 4.1). In the "advance
peaks" of pupation, males greatly outnumbered females at all
temperatures. In the first major pupation peak from 220C to
340C, 69.8% were males; from 240C to 310C, females were the
dominant sex pupating in the second major peak, while at lower
or higher temperatures the sexes were nearly equal. In the
third and subsequent pupation peaks females outnumbered males
at all temperatures (Table 4.1).

From hatching to pupation, mean developmental time
decreased from 232 hr at 220C to 126 hr at 300C, then
increased to 130 hr at 340C (Table 4.2). The time of day of
pupation peaks varied from 2.5 hr before sunset above 300C to
close to midnight at 220C (Table 4.2). Synchrony of develop-
ment in daily peaks, which is measured by calculating the
standard deviation of the daily pupation peaks within a group,
decreased from approximately 4.6 hr at 220C to only 1.6 hr at
340C (Table 4.2). As the temperature rose, therefore, the
synchrony of development within a day's cohort increased very
sharply until at temperatures above 320C over two-thirds of
the day's pupation was concentrated in a 3-hr period.
Synchrony within broods in populations reared at temperatures
from 220C to 340C was greatest at temperatures from 270C to
290C (Table 4.2). From 260C to 310C three indications of
brood synchrony occurred: (1) the highest percentage of
pupations was in the first three peaks, 81.3% to 94.9%, (2)
the greatest concentration of pupations was in two successive
peaks, 74.8% to 84.8%, and (3) the greatest concentration of
pupations was in one peak, 41.7% to 64.0% (Table 4.2). The
highest figure in each case was between 270C and 290C, the
same range as that producing the fastest brood development
(Table 4.2). Whatever the criteria, therefore, brood develop-
pment was most synchronized between 270C and 290C and not at
the highest temperature, as with a day's cohort.

Disregarding the actual times of day, pupation peaks were
spread at 24-hr intervals starting at 84 hr after hatching at
temperatures from 300C to 340C (Table 4.3). The departures
from the 24-hr rhythm were slight, especially for the
important pupation peaks from the 5th to the 8th day
(underlined in Table 4.3), which encompassed 84% of all
pupations for all experiments combined. These four
consecutive peaks occurred on the average approximately an
hour ahead of the theoretical 108, 132, 156, and 180 hr--
since-hatch demanded of an inflexible 24-hr rhythm. That
temperature had little effect on the 24-hr rhythm is evident
from a comparison of the mean number of hours at all
temperatures with the range of the means.


26






Temperature affected the larval duration of each day's
pupation in an expected manner within the range of means. For
each day, larval age at pupation decreased with increasing
temperature (Table 4.3). It is notable, however, that from
the 5th to 8 days, larvae pupated more rapidly at 28C to 31C
than at 32C or higher.

Pupation peaks at temperatures from 220C to 340C revealed
the great tendency for pupation to be concentrated as near as
possible to the threshold set by temperature, the threshold
being the shortest time between hatching and pupation,
regardless of time of day when hatched. The proportion of
pupations nearest the threshold is greatest at temperatures
from 26C to 310C, the range previously reported as optimal
for brood synchronization.

The pupation peak means in Ae. sollicitans occur at 09.69
at 270C and have a large standard deviation of 4.08 hr,
indicating that pupation is not as synchronized as it is in
Ae. taeniorhynchus.

Effect of diet, larval density and water salinity on
endogenous circadian rhythm of pupation.

Three factors -- the diet, larval density, and water
salinity when tested at high and low combinations of each
factor at 270C under LD 12:12, show an effect on the onset
and duration of pupal ecdysis as well as the endogenous
pupation rhythm in Ae. taeniorhynchus. Different diets (basic
ration and 2-times basic ration) and larval densities (75 and
200 larvae per pan) in 10% seawater do not alter the onset of
pupal ecdysis but do affect the total duration of pupation
(Fig. 4.4A, 4.4B, 4.4D, 4.4F). The number of pupation peaks
increased from two to five and the period between the peaks
lengthened from 22.3 to 23.6 hr on the lower diet (Fig. 4.4A,
4.4B, 4.4D). Higher salinities (50% seawater) delayed the
onset and increased the duration of pupation, although
additional food shortened the total duration of pupation even
in high salinities (Fig. 4.4C, 4.4E, 4.4G, 4.4H). The number
of pupation peaks in 50% seawater varied from six to eight,
and the period between the means of peaks was about 24.0
hours.

The effects of environmental factors on larval and pupal
development, as observed in the laboratory, do not differ to a
marked degree from those observed in the field. The average
daily temperature of water in the salt marsh at Vero Beach
varies from March to September between 270C and 300C, when
larvae of Ae. taeniorhynchus are most abundant. The water
temperature during this period shows little diurnal variation,
except in shallow, sunlit pools. The duration of the aquatic


27








Table 4.2. Developmental times of pupation peaks of Aedes taeniorhynchus at temperatures
between 220C and 340C. A. Percentage of pupations in peak. B. Mean number
of hours since hatch. C. Mean time of day for pupation peak (minutes
converted to decimal of hour). D. Standard deviation, in in hours away from
mean time.


A B C D A B C D A B C D

Peak No. 220 230 240

1 12.6 192.0 05.96 4.6 4.9 164.8 02.82 3.4 2.3 139.9 01.85 2.1
2 33.7 212.3 02.30 4.7 37.6 182.1 20.10 4.8 38.0 157.7 19.72 4.1
3 21.9 233.5 23.45 4.8 20.8 205.9 19.90 4.2 35.8 179.4 17.37 3.8
4 18.2 255.5 21.48 4.0 18.6 230.7 20.15 3.9 16.9 203.8 17.83 3.5
5 11.1 280.8 22.77 4.7 14.4 253.1 19.07 4.1 6.9 227.1 17.12 3.2
6 2.5 305.2 23.22 3.1 3.7 277.9 19.92 2.2

Tot. / m 100 232.1 00.47 4.6 100 209.0 20.23 4.2 100 177.7 18.52 3.8

25u 26u 27u

1 11.4 136.3 22.25 3.7 0.1 118.0 04.00 7.0 110.5 20.48 2.0
2 42.1 156.1 18.17 3.0 41.7 133.1 19.13 3.6 64.0 130.5 16.88 2.6
3 18.2 179.9 17.93 2.7 40.5 154.1 16.08 2.4 20.8 153.5 15.45 2.8
4 22.0 202.6 16.55 2.5 13.0 178.3 16.25 2.0 8.2 177.6 15.60 2.1
5 6.3 226.2 16.15 3.2 4.7 200.0 14.02 2.1

Tot. / m 100 172.8 18.10 2.9 100 150.6 17.30 2.8 100 137.7 16.73 2.6






30


280


1 16.8 108.8 18.77 2.1 26.6 107.6 17.60 2.3 0.2 90.0 00.00 --
2 55.4 130.0 15.97 2.4 48.2 130.7 16.72 2.0 37.5 106.2 16.15 2.8
3 22.1 153.2 15.18 1.6 20.1 152.5 14.48 1.9 44.0 129.0 15.02 2.2
4 6.7 177.1 15.13 1.9 5.1 174.4 12.43 2.1 14.7 152.3 14.42 2.0
5 3.6 174.7 12.72 1.8

Tot. / m 100 134.9 16.18 2.1 100 131.2 16.17 2.1 100 125.5 15.27 2.4

31u 320 33u

1 0.4 86.5 20.00 1.5 85.3 19.33 1.3 0.5 83.7 17.67 1.7
2 47.1 105.8 15.82 2.3 37.7 106.4 16.43 1.9 34.4 106.6 16.55 1.4
3 33.8 129.3 15.33 1.5 31.7 130.3 16.33 1.3 39.0 130.1 16.08 1.5
4 16.3 152.1 14.23 1.8 23.3 152.9 14.90 1.7 20.6 153.2 15.22 1.6
5 2.4 175.0 13.03 1.8 5.8 177.0 15.00 2.1 5.5 175.7 13.67 1.9

Tot. / m 100 129.9 15.35 1.9 100 128.6 16.00 1.7 100 129.1 15.93 1.5

34u

1 1.5 83.8 17.80 1.2
2 35.0 106.3 16.33 1.5
3 31.4 130.0 15.95 1.4
4 26.2 153.1 15.05 1.9
5 5.9 176.4 14.42 1.2

Tot. / m 100 129.8 15.28 1.6


290











Table 4.3.


Larval development times (in hours) from hatching to successive pupation peaks in
Aedes taeniorhynchus at temperatures from 220C to 340C.


LARVAL DURATION

Days: 3 1/2 4 1/2 5 1/2 6 1/2 7 1/2 8 1/2 9 1/2 10 1/2 11 1/2 12 1/2
Hrs: 84 108 132 156 180 204 228 252 276 300

22u 192.0 212.3 233.5 255.5 280.8 305.2
230 164.8 182.1 205.9 230.7 253.1 277.9
240 139.9 157.7 179.4 203.8 227.1
250 136.3 156.1 179.9 202.6 226.2
260 118.0 133.1 154.1 178.3 200.0
270 110.5 130.5 153.5 177.6
290 107.6 130.7 152.5 174.4
300 90.0 106.2 129.0 152.3 174.7
310 86.5 105.8 129.3 152.1 175.0
320 85.3 106.4 130.3 152.9 177.0
330 83.7 106.6 130.1 153.2 175.7
340 83.8 106.2 130.0 153.1 176.4


Number of
larvae: 48
Mean hours:84.89
Departure
from mean: +0.89


2816 4739 3403
106.69 130.58 154.39


1903 1154 631
180.12 206.62 230.79


-1.31 -1.42 -1.61 +0.12 +2.62 +2.79


381 170 28
254.40 280.03 305.21

+2.40 +4.03 +5.21


0








QA/IT/TTY SE4-ifAR i LAVMmE
2- OFFOOD o DLtLCO6(oI) PERPW
A / BR /0 75



i30i

0o-
,o- 8 ;: /' *aR** ;- /o 7




30- ,
50- ,
30

I 2BR /0% 75


20so-




60-
50-
o40-
30-
20-



20- BRA 50* o 0 zoo
o. V .......... -.. .......... .. _
i0- G A,
50-




-96 RD U W, 6 J 40o 2M ON 31
HURS AFTER MATCH




Fig. 4.4. Sequence of pupation (solid line) and emergence
(dotted line) in Aedes taeniorhynchus as affected by
paired combinations of food quantity (BR), larval density
(number of larvae), and salinity (% of seawater) at 270C
and under LD 12:12. Ordinate: 2-hour running average of
number of pupae and adults per hour (modified from Nayar
1967b).

stages -- i.e., from egg hatch to emergence -- varies from 6
to 8 days in warm weather to 12 to 15 days in cool weather
(Nielsen and Nielsen 1953). The daylength at Vero Beach
ranges from a minimum of 10.5 hr from the end of December to a
maximum of 14.5 hr in the middle of July. The condition which


31






changes dramatically in nature is the osmotic concentration of
the water, ranging from close-to-fresh water during the rainy
season to almost seawater concentrations in the dry season or
following tidal flooding. Larvae in the salt marsh often are
densely crowded and confronted with insufficient food for
rapid growth. These variable conditions often result in the
production of several diurnal peaks of pupation.

ADULT EMERGENCE

Nielsen and Haeger (1954) demonstrated that the time of
the day of emergence of Ae. taeniorhynchus varied, whereas the
antecedent pupation peaks occurred only in the afternoon.
They postulated that emergence peaks occurred during any time
of the day because the pupal duration was determined only by
temperature. This was supported later by showing the rigid
dependence of pupal duration on temperature (Nielsen and Evans
1960, Provost and Lum 1967). Nayar (1967b) showed that for
pupae reared under different rearing conditions at the same
light regime and temperature conditions, the emergence peaks
occurred after 41 hr at 270C (Fig. 4.4). The duration of the
pupal stage in Ae. taeniorhynchus females varies from 150 hr
at 16 C, to about 30 hr between 330C and 360C (Table 4.4)
(Nielsen and Evans 1960).

Table 4.4. Pupal duration for males and females of Aedes
taeniorhynchus, computed from developmental
velocities given by Nielsen and Evans (1960).

Temperature Duration of pupal stages (hrs)

(C) Male Female

16.0 145.56 149.92
19.5 89.21 90.91
20.0 82.58 83.33
24.0 52.91 53.68
26.0 43.76 44.90
28.5 37.57 37.05
32.0 31.10 31.75
36.0 29.90 30.45


SYNCHRONIZATION OF EMERGENCE

In the laboratory, maximum synchronization of pupation is
achievable under a certain combination of conditions of
temperature and diet; therefore, the subsequent emergence
rhythm would show maximum synchronization at the same
temperature (Provost and Lum 1967). If a synchronized
emergence is desired at a certain time of the day, this could


32






be attained by selecting an appropriate temperature for the
pupal stage.

Synchronization of the emergence peak can also be
achieved from an asynchronous larval brood by separating the
newly formed pupae at 4-hr intervals and maintaining them at
low temperatures until 90% of the larvae pupate. Pausch and
Provost (1965a,b) produced synchronous emergence in the
field nursery plots at a predetermined time by this method.
They synchronized emergence in a brood by reducing the
emergence period from 40 hr to 12 hr, with over 50% of the
emergence compressed into 2 hours.

EFFECT OF LARVAL NURTURE ON DISPERSAL AND MIGRATORY BEHAVIOR

Knowledge of the degree of synchronization of pupal
development of a brood of Ae. taeniorhynchus is paramount in
determining the nature of the adult departure from the site of
emergence. Since synchronization is mediated primarily by the
circadian rhythm of pupation, an understanding of larval and
pupal development is necessary to interpret field observations
adequately. Temperature alone determines duration of the
pupal stage when larvae are reared on optimal diet (Nielsen
and Evans 1960, Nayar 1967b, Provost and Lum 1967).
Therefore, the emergence rhythm is a replication of the
pupation rhythm, separated by a time interval determined by
the water temperature. The time of the day when an emergence
pulse occurs has a profound bearing on the age and
physiological state of adults at twilight and hence on the
time and manner of their departure from the breeding area.
All these, in turn, control the migration and dispersal
behavior of the brood. The results of the experiments
described previously in conjunction with what is known from
the field observations, explain the relationship between the
circadian rhythm of pupation and adult migration and dispersal
in Ae. taeniorhynchus.

The data from Table 4.2 for the combined pupation peak at
temperatures from 220C to 320C serve as the starting point for
a schematic presentation (Fig. 4.5) of events from pupation to
adult departure from the site of emergence (Provost 1974).
This main peak always appears one day after the threshold of
pupation has been reached. When the complexity of the
situation in nature is recalled, a schematic presentation like
this can readily be accused of being but a compounding of
oversimplifications. For example the hatching of a brood of
Ae. taeniorhynchus in. a salt marsh is more likely to be spread
over several hours than concentrated in 15 min as in experi-
mental populations. The food supply may vary with location and
time, as will larval densities, temperatures, and even
salinities. The credibility of Fig. 4.5 is nevertheless
established by two important considerations: (1) the net


33






effect of the diurnal rhythm of pupation is to reestablish a
synchrony of development otherwise lost in a welter of differ-
ing environmental conditions (Provost and Lum 1967) and
(2) while temperatures in nature fluctuate, the mean over a
span of several hours in no way differs in its effect on adult
emergence from an equivalent constant temperature. The second





PUPATION EMERGENCE EXODUS
(PUPAL DURATION IN HRS) (AGE IN HRSJ

311 II 300l l^

...... . MONTHLY MEAN(42' )
-31 115F AIR TEMPERATURES
SAT E.R.C. 1957-1966


Ax ------- -


6 A ESEPT. .28.0
SI i .. .. JULAUG. 2," 5'
E ii l ll ..J.l li .JU N E2 0

















Fig. 4.5. Schematic presentation of pupation peaks and time of
emergence peaks in Aedes taeniorhynchus, showing age at
exodus. The vertical shaded bar representing night is tapered








from 10 hours a 32C to 14 hours at 22C to approximate the

change in photoperiod from summer to winter. Open triangles
show times of pupation and the subsequent emergence. An arrow
at twilight indicates an exodus. Departures during the night
are indicated by triangles representing that portion of the

antecedent emergence which was not old enough to depart at
twilight. At 25C, the nocturnal triangle is cut off to
exclude those adults which had emerged at night and would then
have to wait until the next twilight to depart (from Provost
1974).


34






point was demonstrated not only in the laboratory (Nayar
1967b) but in the field (Pausch and Provost 1965a), where
pupae were manipulated into timed exposures to varying
temperatures, and the temperature-summation concept was used
to achieve an emergence. From these and other convincing
experiences, Fig. 4.5 appears to have predictive validity.

The seasonal air temperature pattern at Vero Beach is
like that of the entire Florida peninsula. Winter means,
December to February, stay generally between 160C and 180C.
The three spring months cover the rise in mean temperature
from 190C to 250C. During the summer months, June to
September mean temperatures remain very steadily between 260C
and 280C. In the two fall months, mean temperatures drop
rather precipitously toward the winter levels. The relation of
air temperature to water temperature in the shallows where Ae.
taeniorhynchus usually breeds has been repeatedly observed
here. The usual situation is for the water temperature to
exceed air temperature by day, and sometimes very consider-
ably, while at night water and air temperatures are mostly
equal. The net effect is for the water temperature, as a 24-
hr mean, to be 10C to 40C above the air temperature, with the
most frequent difference being 20C. Accordingly, in Fig. 4.5,
air temperatures plus 20C are added for the main breeding
season of Ae. taeniorhynchus, May to October. These can then
be directly compared with the actual water temperatures of the
experiments.

The control of pupation time by the light cycle and of
emergence time by temperature is seen clearly in Fig. 4.5.
Pupation peaks remain in the latter part of the afternoon at
all temperatures except those normally encountered in the
spring and fall only, when they shift into the dark hours
toward midnight. In marked contrast, emergence peaks occur
both night and day, shifting from midnight at 320C to midnight
a day later at 240C. In the emergence peak at 32C, four
standard deviations (base of triangle) are easily encompassed
within the night, whereas at 240C they extend into daylight
before sunset and after sunrise.

On the basis of the previously described conditions and
time for emergence peaks, departure of newly emerged adults
can now be projected. At water temperatures from 280C to
320C, which prevail in Vero Beach during the summer, all the
new adults are over 6 hr of age before sunset, and the mass
exodus, so often observed, will occur. Within the rane of
spring and fall expected mean water temperatures, 24 C to
27C, the mass exodus at twilight is still the most likely
type of departure. However, in the neighborhood of 260C, the
emergence is late enough in the afternoon that the great
majority of new adults reach the minimum permissive age for


35






departure during the night. It can therefore be expected
that if conditions are just right, in the spring or fall,
there may be a small exodus at twilight followed by individual
departures during the night more or less repeating the time
pattern of the emergence pulse (Provost 1974). This is what
happened in 1952 (Provost 1957), as mentioned earlier.
Although it was mid-June, more spring-l e temperatures
prevailed in the wooden tanks holding the P-marked fourth
instars and pupae because they were shielded from the sun by a
canvas fly. The water temperature remained between 230C and
280C and averaged 25.50C.

The effects of larval nurture and neonate potentialities
on emergence and dispersal can now be considered. It has been
shown (Lum et al. 1968) that maximum synchronization of
development in this mosquito is achieved (1) in the presence
of abundant food, (2) at sunrise hatching of an alternating
day and night regime, and (3) at water temperatures between
290C and 320C. It follows, then, that the greatest crowding
of newly-emerged adults will occur, in nature, in broods
hatched near sunrise, in water rich in nutrients, and during
summer warm spells. (A daily mean air temperature of 300C is
reached in Vero Beach only on extremely hot summer days.) The
effect of adult crowding on the migratory drive in insects is
much less understood than that of immature crowding (Johnson
1969), and in many cases, as with Ascia monuste, the butterfly
migrant and cohort of Ae. taeniorhynchus, larval and adult
crowding effects are scarcely separable (Nielsen 1961).

Synchronization of growth is also enhanced by larval
aggregations. Larval aggregation, a pronouncedly summer
phenomenon in nature, produces in the laboratory the migrant
type of Ae. taeniorhynchus adults (Nayar and Sauerman 1969)
characterized by a strong burst of spontaneous flying at the
first change from light to dark, a condition equivalent to the
twilight exodus in nature. The adult mosquitoes resulting
from non-aggregating larvae fly little, by comparison with the
migrant mosquitoes, either at the first twilight or during the
ensuing night, or, for that matter, during the next two
nights. This would thus suggest that the non-migrant mosquito
is physiologically delayed compared with the migrant mosquito.

MECHANISMS OF IONIC AND OSMOTIC REGULATION IN LARVAE

The larvae of Ae. taeniorhynchus and Ae. sollicitans
thrive both in fresh water and saline waters, even though the
latter may be considerably hyper-osmotic (at least two to four
times) relative to the hemolymph (Carpenter and LaCasse 1955,
Bradley and Phillips 1975, Nayar and Sauerman 1974). The
highest salinity tolerance reported to date is that of Ae.
taeniorhynchus larvae in seawater three times as concentrated
as normal seawater (572 mM NaCl/L). These larvae can adapt to

36






such varying conditions without steady-state hemolymph
concentrations of Na Mg K Cl- and total solutes
(osmolality) changing by more than twofold, except in very
fresh water (NaC1 <1-2 mM). Regulation to changes in sulphate
concentration is less successful. The hemolymph concentration
of this ion is maintained at low levels (<10 mM) until the
external concentration rises above 100 mM; thereafter, the
blood level rises in parallel with external values until it
reaches 100 mM and reaches an equilibrium. There are no
obvious detrimental effects to the larvae over the next
several days, but at highest tolerable concentrations of
seawater, both rate of larval development and morphological
characteristics may be adversely affected (Nayar and Sauerman
1974, Bradley and Phillips 1977a).

Malpighlan tubules, the rectum, and the extrarenal organs
(anal papillae) are responsible for osmotic regulation in Ae.
taeniorhynchus larvae. The total body content of water and
salt is turned over relatively slowly in fresh water; with
increasing salinity of the external medium, however, a
dramatic reduction in turnover time is observed. This is
largely caused by the increased ion concentration in the
ingested fluid, ingestion being virtually the only means of
entry of water and most ions from hypertonic media (Bradley
and Phillips 1977a). There is little difference observed in
drinking rate by Ae. taeniorhynchus larvae reared in 10%,
100%, or 200% seawater (Bradley and Phillips 1977b). The
drinking rate is proportional to body surface area, as
expected if it is dictated by the metabolic demands for
nutrients. Indeed, larvae can be reared in a sterile culture
medium in the absence of particulate matter or organisms
(Nayar 1966, Clements 1963). Since many natural saline waters
in which larvae thrive are undoubtedly rich in dissolved
nutrients and microorganisms, larvae may normally indiscrimi-
nately ingest the external medium as a means of obtaining
nutrients (Phillips et al. 1978).

Malpighian tubules: Each larva has five tubules of
similar appearance and without obvious divisions into distinct
segments under a light microscope, but containing two cell
types based upon ultrastructure: primary cells and stellate
cells (Bradley et al. 1982). In this regard the tubules are
identical to the Malpighian tubules of adult Aedes aegypti, a
strictly freshwater species (Mathew and Rai 1976). The
majority of cells in the tubules are primary cells, the larger
of the two types; these cells have an abundance of intra-
cellular membrane-bound crystals and two types of microvilli
on the luminal surface, i.e., those with internal mitochondria
and those without. The stellate cells are much smaller, lack
intracellular crystals, and have microvilli without internal
mitochondria. While Malpighian tubules of saline-water
mosquito larvae may not be unusual in their mechanisms of


37






fluid secretions, they have an unusual ability to secrete
divalent ions. Active transport of Mg + and SO4 can occur
against large electrochemical gradients under appropriate
experimental conditions (Maddrell and Phillips 1978).

Rectum: The anterior and posterior rectal segments have
separate functions (Bradley and Phillips 1977b). The two
segments show ultrastructural dissimilarities, the cells of
the posterior segment having deeper apical infolds more
closely associated with mitochondria. Electrical potential
differences relative to the hemolymph are of opposite sign in
the two segments, with the anterior being negative and
posterior positive. An in vitro ligated preparation of the
posterior rectal segment secretes a strongly hyperosmotic
fluid while the anterior does not.

Anal papillae: Ultrastructural studies show that the anal
papillae contain only one cell type, arranged as a single
layer, covered with a cuticle externally. Internally only a
basement membrane separates the cell from the haemocoel. Both
apical and basal borders are highly folded. The ultra-
structure suggests active transport activity under all
conditions. The role for anal papillae is to actively absorb
ions present in the external environment at only relatively
low concentrations: e.g., Cl and K+ (Phillips et al. (1978).

Ionic and osmotic regulation: Phillips et al. (1978)
proposed that the following events occur in saline-water
larvae adapted to fresh water. The Malpighian tubules secrete
an iso-osmotic fluid rich in K+ and Cl-. These two ions and
possibly others (e.g. Na ), as well as essential metabolites,
are reabsorbed in the anterior rectum with a minimum of
water. This creates a hypo-osmotic fluid containing largely
nitrogenous and other waste products; the system functions
much like that of freshwater insects (Stobbart and Shaw
1974). Under these conditions the posterior rectum is
inactive, and fluid passes through this segment to the
exterior without major change. Net uptake of K Na and Cl-
occurs through the anal papillae in any natural fresh water
containing more than 0.1 mM of these ions.

In larvae adapted to hyperosmotic waters, the Malpighian
tubules continue to produce iso-osmotic fluid rich in KC1.
However, if the water contains high levels of Mg or SO,
active secretion of these ions is induced and accounts for a
significant fraction of the total solute in the tubule fluid.
An increase in transport capacity, i.e., amount of carrier for
S02 2+
SO4 and possibly for Mg rapidly occurs (within a period of
a day) in response to exposure of the larvae to water contain-
ing high levels of these ions. In the anterior rectum, most
of the KC1 and water is reabsorbed in proportional amounts,
leaving a smaller volume of approximately iso-osmotic fluid

38






enriched in MgS04 and other waste products. The posterior
rectum is activated and secretes a hyperosmotic fluid. The
relative rates at which it eliminates the various ions (Na+,
K Mg2+, Cl and HC03) depend on the concentration of these
ions in the external medium to which the larvae are adapted,
as well as the hemolymph levels. In more concentrated waters,
the total rate of ion transport by the posterior rectum and
the volume of its secretion increase. However, proportionally
less water follows the ion movement, so that osmolarity of the
secretion also increases. This fluid is then eliminated via
the anus. Net uptake of individual ions from the external
medium may continue via the anal papillae in unbalanced
waters; e.g., Cl uptake from NaHCO3 water poor in Cl-. In
seawater, in which both Na+ and Cl are more concen-trated
than in the hemolymph, uptake of these ions by the anal
papillae ceases. Indeed the papillae may now transport Na
and Cl- in the opposite direction, and thus eliminate them
from the larva. Phillips et al. (1978) suggest that some of
the Na+ secreted in this manner might be linked to a net
influx of K as occurs in the gills of marine teleosts. This
would help to replace the large quantities of K+ lost by
secretion in the posterior rectum.


39






REFERENCES CITED


Anderson, J. F.
1970. Induction and termination of embryonic diapause in
the salt marsh mosquito, Aedes sollicitans
(Diptera: Culicidae). Bull. Conn. Agric. Exp.
Station New Haven No. 711. 22 pp.
Bradley, T. J., and J. E. Phillips.
1975. The secretion of hyperosmotic fluid by the rectum
of a saline-water mosquito larva, Aedes
taeniorhynchus. J. Exp. Biol. 63: 331-342.
1977a. The effect of external salinity on drinking rate
and rectal secretion in the larvae of the saline-
water mosquito Aedes taeniorhynchus. J. Exp.
Biol. 66: 97-110.
1977b. The location and mechanisms of hyperosmotic fluid
secretion in the rectum of the salt-water mosquito
larva Aedes taeniorhynchus. J. Exp. Biol. 66:
111-126.
Bradley, T. J., A. M. Stuart, and P. Satir.
1982. The ultrastructure of the larval Malpighian tubules
of the saline-water mosquito, Aedes taeniorhynchus.
Tissue and Cell 14: 759-773.
Carpenter, S. J., and W. J. LaCasse.
1955. Mosquitoes of North America (North of Mexico).
Univ. Calif. Press, Berkeley. vi + 360 pp, illus.,
127 pits.
Clements, A. N.
1963. The Physiology of Mosquitoes. The Macmillan Co.,
New York. 393 pp.
Horsfall, W. R., P. T. M. Lum and L. M. Henderson.
1958. Eggs of flood water mosquitoes (Diptera:
Culicidae). V. Effect of oxygen on hatching of
intact eggs. Ann. Ent. Soc. Am. 51: 209-213.
Horsfall, W. R., H. W. Fowler, Jr., L. J. Moretti, and J. R.
Larsen.
1973. Bionomics and Embryology of the Inland Floodwater
mosquito, Aedes vexans.. Univ. of Illinois Press,
Urbana. 211 pp.
Johnson, C. G.
1969. Migration and dispersal of insects by flight.
London: Methuen. 763 pp.
King, W. V., G. H. Bradley, C. N. Smith, and W. C. McDuffie.
1960. A Handbook of the Mosquitoes of the Southern United
States. U. S. Dept. of Agriculture. Agri.
Handbook 173. 188 pp.
Lum, P. T. M., J. K. Nayar, and M.W. Provost.
1968. The pupation rhythm in Aedes taeniorhynchus
(Wiedemann) (Diptera: Culicidae). III. Factors in
developmental synchrony. Ann. Ent. Soc. Am. 61:
889-899.


40






Maddrell,, S. H. P., and J. E. Phillips.
1978. Induction of sulphate transport and hormonal
control of fluid secretion by Malpighian tubules of
larvae of the mosquito Aedes taeniorhynchus. J.
Exp. Biol. 72: 181-202.
Mathew, G., and K. S. Rai.
1976. Fine structure of the Malpighian tubule in Aedes
aegypti. Ann. Ent. Soc. Am. 69: 659-661.
Moore, R. C., and W. E. Bickley.
1966. Hatching of the eggs of Aedes taeniorhynchus
(Wiedemann) (Diptera: Culicidae) in response to
temperature and flooding. Mosquito News
26: 405-415.
Nayar, J. K.
1966. A method of rearing salt-marsh mosquito larvae in a
defined sterile medium. Ann. Ent. Soc. Am. 59:
1283-1285.
1967a. Endogenous diurnal rhythm of pupation in a mosquito
population. Nature 214: 828-829.
1967b. The pupation rhythm in Aedes taeniorhynchus
(Diptera: Culicidae). II. Ontogenetic timing,
rate of development and endogenous diurnal rhythm
of pupation. Ann. Ent. Soc. Am. 60: 946-971.
1968. The pupation rhythm in Aedes taeniorhynchus.
IV. Further studies of the endogenous diurnal
(circadian) rhythm of pupation. Ann. Ent. Soc.
Am. 61: 1408-1417.
Nayar, J. K., and D. M. Sauerman, Jr.
1969. Flight behavior and phase polymorphism in the
mosquito Aedes taeniorhynchus. Entomologia Exp.
Appl. 12: 365-375.
1970. A comparative study of growth and development in
Florida mosquitoes. Part 1. Effects of environ-
mental factors on ontogenetic timings, endogenous
diurnal rhythm and synchrony of pupation and
emergence. J. Med. Ent. 7: 163-174.
1974. Osmoregulation in larvae of the salt-marsh
mosquito, Aedes taeniorhynchus Wiedemann.
Entomologia Exp. Appl. 17: 367-380.
Nielsen, E. T.
1961. On the habits of the migratory butterfly Ascia
monuste L. Biol. Medd. 23: 1-81.
Nielsen, E. T., and D. G. Evans.
1960. Duration of the pupal stage of Aedes taeniorhynchus
with a discussion of the velocity of development as
a function of temperature. Oikos 11: 200-222.
Nielsen, E. T., and J. S. Haeger.
1954. Pupation and emergence in Aedes taeniorhynchus
(Wied.). Bull. Ent. Res. 45: 757-768.
Nielsen, E. T., and A. T. Nielsen.
1953. Field observations on the habits of Aedes
taeniorhynchus. Ecology 34: 141-156.


41






O'Meara, G. F.
1975. Lethal traits associated with the bleached-eye
color mutant of Aedes taeniorhynchus. Ann. Ent.
Soc. Am. 68: 157-162.
Pausch, R. D., and M. W. Provost.
1965a. The dispersal of Aedes taeniorhynchyus.
IV. Controlled field production. Mosquito News
25: 1-8.
1965b. The dispersal of Aedes taeniorhynchus. V.
A controlled synchronous emergence. Mosquito
News 25: 9-14.
Phillips, J. E., T. J. Bradley, and S. H. P. Maddrell.
1978. Mechanisms of ionic and osmotic regulation in
saline-water mosquito larvae. Pp. 151-171 in
Comparative Physiology: Water Ions and Fluid
Mechanisms, K. L. Schmidt-Nielsen, L. Bolis, and S.
H. P. Maddrell, eds. University Press, Cambridge,
England 360 pp.
Provost, M. W.
1952. The dispersal of Aedes taeniorhynchus. I.
Preliminary studies. Mosquito News 12: 174-190.
1957. The dispersal of Aedes taeniorhynchus. II. The
second experiment. Mosquito News 17: 233-247.
1974. The dispersal and migration of mosquitoes. In
Proceedings Mosquito Abatement Seminar and Work
Conference at University of Manitoba, Canada, R. A.
Brust and A. J. Thorsteinson, eds. pp. 4-39
(Mimeo.)
Provost, M. W., and P. T. M. Lum.
1967. The pupation rhythm in Aedes taeniorhynchus
(Diptera: Culicidae). I. Introduction. Ann. Ent.
Soc. Am. 60: 138-149.
Stobbart, R. H., and J. Shaw.
1974. Salt and water balance excretion. Pp. 362-446 in
The Physiology of Insects. M. Rocksteen, ed., 2nd
ed. Vol. 5, Academic Press, New York.


42






CHAPTER 5


LARVAL BEHAVIOR

J. R. Linley

In their early field observations on Aedes taenio-
rhynchus, Nielsen and Nielsen (1953) provided the first
description of the larval behavior of this species. First
instar larvae are able to remain for extended periods at the
bottom of natural pools since they are small enough to sustain
their respiratory needs by gaseous exchange through the
cuticle. As they grow older, they periodically return to the
surface to breathe and, in the fourth instar particularly, are
seen to congregate in large masses at various locations in the
water. These masses of larvae ultimately become extremely
dense. They may be comprised of many hundreds or even
thousands of individuals (Fig. 5.1) and assume a configuration
referred to as "balling up" by Nielsen and Nielsen (1953).
Although the masses of larvae observed by these authors were
described as having a circular outline, or spheroidal in
larger masses, this was probably an impression gained from the
distribution of larvae at the surface. These individuals to a
large extent conceal the shape, to be described shortly, of
the remainder of the mass below the surface.

A brief summary description will be given here of the
behavioral responses upon which the "balling" activity is
based, followed by a generalized explanation of the shape of
these masses and how they are sustained. The data are from a
series of extensive laboratory and field observations (J. R.
Linley, F. D. S. Evans, and H. T. Evans, unpublished).

Nayar and Sauerman (1968) observed that the larvae of Ae.
taeniorhynchus are negatively phototactic. The larvae have
two eyes and their response to light may, in fact, be assumed
to be phototropotactic (Fraenkel and Gunn, 1961), with the
level of stimulus at each eye compared rapidly but alternately
(rather than simultaneously), owing to the side to side move-
ments of the head during swimming. Rather than the single
response of negative phototaxis, closer observation shows that
there are three phases of larval response to light, continu-
ously traversed by larvae as they leave and return to the
surface. When larvae initiate swimming and leave the surface,
they exhibit negative phototropotaxis, which, in laboratory
experiments persisted for 59% of the subsurface period
(unpublished data). Following this, the larvae enter a phase
(21% of the subsurface period) in which they move neither
towards nor away from light, but swim perpendicularly to the
source of illumination. According to the system of Fraenkel
and Gunn (1961), this is a "dorsal light reaction," but it is


43






obvious only under certain conditions (to be discussed in a
later paper) in Ae. taeniorhynchus larvae because they almost
always have swum down and reached the bottom substrate by the
time the dorsal response begins. In the final phase, the
larvae become positively phototactic (20% of the subsurface
period) and swim towards light. Under natural conditions,
this leads, of course, to a return to the surface, where, with
the exchange of tracheal gases, the larvae revert to a photo-
negative condition within a few seconds (unpublished data).


Fig. 5.1. A mass of Aedes taeniorhynchus larvae in the
field.

In a mass of larvae in the field, shown in generalized
lateral view in Fig. 5.2, the larvae at the surface form a
layer one individual deep, dispersed almost invariably in a
circular or ovoid formation, with individuals more densely
packed towards the center. Very often, there is some central
up-welling of water, as it is here where most larvae arrive at
the surface. The density decreases towards the periphery, as
it is predominantly from here that larvae initiate the next
dive. As larvae leaving the surface are negatively photo-
tactic, they usually swim along an inward and downward curve
(Fig. 5.2), perhaps mingling to some extent near the bottom
with individuals that are beginning to ascend. Once a larva


44


'^WM ^*^ irri~71






has joined the mass of other individuals at the bottom, where
light intensity is considerably reduced, it swims relatively
little, and such movement as occurs is accomplished by
currents generated as the mouthbrushes browse over the
substrate. However, since the larvae respond negatively to
light for over half the subsurface period, and only a few
seconds are required to swim to the bottom, many larvae at any
given time are tending to seek darker conditions at the center
of the mass on the bottom (Fig. 5.2). Even when larvae enter
the dorsal reaction phase (which is brief), there is probably
little tendency for them to move towards the periphery, as
they swim relatively little, especially when the mouthparts
are in contact with the bottom or other individuals. Once a
larva passes to the photopositive phase, the filtering action
of the mouthparts ceases and individuals often rise under
their own buoyancy for some distance before commencing to swim
actively towards the surface. Many animals probably move some
distance towards the surface before completing their ascent
actively.

From Fig. 5.2, it can be seen that the "balls" of larvae
are actually more in the shape of an I in vertical cross-
section. What adaptive function these masses serve is a
matter of conjecture. It is very obvious in field observations

SI %A ^ft aI) /\ % /- surface






e J, z
.. \ / I I /
r ,











:: ..-... ... bottom




Fig. 5.2. Generalized lateral view of an Aedes taeniorhynchus
larval mass showing paths of larvae (solid arrows) and
currents (dashed arrows) which carry suspended particulate
matter.


45


I,
/



/


.---






of this kind would not occur if larvae were dispersed more or
less evenly in the habitat and were diving singly to the
bottom. Thus, despite presumed effects of competition due to
crowding, formation of these larval masses may augment the
amount of food available to larvae by providing them access to
suspended bottom material throughout the complete "cycle" of
surface and subsurface behavior. This is particularly true
since field observations (unpublished) have shown that the
larval masses move laterally across the water and thus over
the bottom at speeds up to 10 cm/min. Nayar and Sauerman
(1968) observed that Ae. taeniorhynchus larvae temporarily
crowded and starved in pans under laboratory conditions tended
to pupate more synchronously than uncrowded larvae. They
suggested also that perhaps such effects might tend to result
in adults more prone to migrate on emergence.

Under field conditions, highly organized masses of larvae
were observed to persist throughout the diel, although as will
be detailed in a later paper, there is considerable variation
in the structure of the masses and the behavioral details at
different times of the day and night. Temperature, which
ranged during field studies from about 190C to 370 C did not
appear to have any effect upon whether masses of larvae were
present or not.

The temperature responses of Ae. taeniorhynchus larvae
and pupae have been investigated in some detail (Linley and
Evans, 1971). The distribution of all larval instars (both
starved and fed) and pupae in a constant temperature gradient
in special troughs was recorded (Fig. 5.3, Fig. 5.4). Larvae
preferred surprisingly warm temperatures, with the average
preferred temperature increasing from 31.80C for 1st instar
individuals to 33.00C for those in the 4th instar (Fig.
5.3). Starved larvae were generally disposed over a wider
range (owing probably to their greater activity) and tended to
select somewhat cooler temperatures. Pupae also selected
rather warm conditions, with perhaps a slight tendency for the
preferred temperature to increase with age (Fig. 5.4). Larvae
of Ae. taeniorhynchus show a preference for considerably
warmer temperatures than other mosquito species that have been
tested (Linley and Evans, 1971). Perhaps this is to be
expected, considering that Ae. taeniorhynchus inhabits
temporary pools in which there is presumably considerable need
for the larvae to complete development in the minimum time.


46






Instar Number
SStaorved Fed
20-

10- 1,341 1,333
31 8 C

0-
30-

20-
2,789 2,747
10 32 9 *C

0-
40
III


30 -


20 2,120 2,011

0 333 *C



40

30


20- 2,150 2,082

10 34-6 C




30



20 2,404 2,250


10 330%

0

Temperature 'C





Fig. 5.3. Distribution of fed and starved Aedes taenio-
rhynchus larvae in a constant temperature gradient abscissaa).
Numbers (right) are numbers of animals tested; temperature
underlined is average preferred by fed larvae, using portion
of distribution to right of arrow. IV, and IV2 indicate early
and late instar individuals, respectively.


47





40


0.


12-16 hr


-Age
2-6 hr






-


20-24hr


3,299



26146


2,614


5 aio w60 h ,- 0
U y- N C N 10 P0 V It
Temperature *C


Fig. 5.4. Distribution of Aedes taeniorhynchus pupae in a
temperature gradient. Same conventions as Fig. 5.3.


48


30


I


20


10


201


0
0
0.


10


0


201


IO


0
20


10o


OL


Iv"""\\~km\\\\\\\\\


28-32 hr


Number





2,725

310 OC








2,762

313 C


A






REFERENCES CITED


Fraenkel, G. S., and D. L. Gunn
1961. The Orientation of'Animals. Dover Publications
Inc., New York, 376 pp.
Linley, J. R., and D. G. Evans
1971. Behavior of Aedes taeniorhynchus larvae and pupae
in a temperature gradient. Ent. Exp. Appl. 14:
319-332.
Nayar, J. K. and D. M. Sauerman, Jr.
1968. Larval aggregation formation and population density
interrelations in Aedes taeniorhynchus, their
effects on pupal ecdysis and adult characteristics
at emergence. Ent. Exp. Appl. 11: 423-442.
Nielsen, E. T., and A. T. Nielsen.
1953. Field observations on the habits of Aedes
taeniorhynchus. Ecology 34: 141-156.


49






CHAPTER 6


LARVAL AND ADULT NUTRITION AND ADULT EXCRETION

J. K. Nayar and E. Van Handel


EFFECTS OF LARVAL NURTURE ON ADULT CHARACTERISTICS AT
EMERGENCE

Larvae of Ae. taeniorhynchus and Ae. sollicitans, like
larvae of most mosquito species, feed indiscriminately upon
the microplankton of their habitat, including algae, rotifers,
protozoa, bacteria, and fungal spores (cf. Clements 1963). In
the laboratory, however, larvae of Ae. taeniorhynchus and Ae.
sollicitans can be reared successfully on a variety of
suspended particulate foods, like mixtures of brewers yeast
and liver powder, ground rat chow, etc. (Nayar 1967, Lea
1964), as well as under sterile conditions, on a semi-defined
diet consisting of lactalbumin, sucrose, ribonucleic acid,
alphacel, artificial sea water, and a mixture of B-vitamins in
distilled water (Nayar 1966). Expression of body size, body
weight, and energy reserves in the adults at emergence are
dependent on the same five factors (diet type and/or quantity
of food, larval density, water salinity, light regimes, and
temperature), singly and in combination, which affect larval
and pupal development (Nayar 1969, Nayar and Sauerman 1971a).

When larvae of Ae. taeniorhynchus were reared at 270C
under LD 12:12 and different levels of food, larval densities,
and salinities, the amount of food a larva can assimilate
under different salinities was found to be important in
controlling the size, dry weight, energy reserves, and
expression of autogeny of the adults at emergence (Nayar
1969). Below the basic ration (BR), the adults were small,
with low energy reserves and few stage V eggs, whereas at food
levels above the standard, there was no enhanced effect on the
adults (Tables 6.1, 6.2). Small adults with low energy
reserves and few stage V eggs were also produced when larvae
were reared in high salinities or crowded in pans (Table 6.1,
6.2). The maximum expression of adult characteristics was
found when 50 to 75 larvae per pan were reared on high ration
(basic or 2x basic ration) on 0% to 25% seawater at 270C under
LD 12:12 (Tables 6.1, 6.2). Further experiments showed that
with larvae reared on high ration in 10% seawater at different
temperatures from 240C to 340C, although they produced the
largest adults at 240C, the heaviest adults--with maximum
lipid and glycogen reserves, greatest expression of autogeny,
and greater numbers of stage V eggs--were produced at 28 C to
300C. Larvae reared under continuous light produced the
heaviest adults with the most energy reserves, and had the
highest expression of autogeny.


50






Table 6.1. Adult characteristics (means and S.D.) of Ae. taeniorhynchus (Vero Beach strain) after
emergence, when reared at 270C under LD 12:12 under differing levels of food, density,
and salinity.

Mean Weight Energy Reserves Expression of Autogeny**
Wing Length dry body Percentage of % females % females Av. no. of
Rearing (mm) weight dry body weight with stage III with stage V stage V
Condition* Sex S.D. (g) Lipid Glycogen follicles follicles follicles

Food
172 basic ration d 2.6 0.1 309 31.2 8.2 17.5
9 2.6 0.1 617 31.4 10.2 11.9 37.0 0.0 0.0
2 basic ration d 2.9 0.1 697 34.0 11.4 16.9
9 3.0 0.1 987 98.8 12.9 8.3 100.0 75.0 45.6 12.4
Density
50 larvae/pan d 2.9 0.05 780 42.0 12.4 17.8
9 3.0 0.08 1078 23.2 15.0 11.0 100.0 48.7 45.7 11.2
200 larvae/pan d 2.6 0.1 438 23.4 7.6 14.0
9 2.7 0.2 604 15.1 5.8 8.9 70.0 0.0 0.0
Salinity
Tapwater d 2.9 0.16 738 25.7 13.2 14.3
9 3.0 0.1 1033 62.9 13.7 9.6 100.0 70.0 52.0 13.8
100% seawater d 2.5 0.1 374 50.5 5.7 15.5
9 2.5 0.09 509 49.4 6.1 8.5 51.4 34.3 20.1 7.8

*Standard rearing conditions: Basic ration (80 mg Brewer's yeast at 0 hr, 10 mg liver powder at 24 hr, and
40 mg Brewer's yeast at every 24-hr interval for subsequent 6 days), 75 larvae per pan, 300 mL of 10%
seawater.
**Expression of autogeny was determined in non-mated females maintained for 4 days on a 10% sucrose solution,
modified from Nayar (1969).


~- -^








Table 6.2. Adult characteristics (means S.D.) of Aedes taeniorhynchus (Vero Beach strain) and Aedes sollicitans
(Vero Beach strain) and expression of autogeny in Ae. taeniorhynchus after emergence, when larvae were
reared at 270C under LD 12:12 under varying conditions from standard.

Expression of Autogeny**
% females
Weight Energy Reserves with stage % females Av. numbers
Wing Mean dry Percentage of III and with stage of stage V
Rearing Length weight/adult dry body weight above V follicles/
Conditions Sex (mm) ( g) Lipid glycogen follicles follicles females


Aedes taeniorhynchus
a) standard condition*
b) 50% SW
c) 200 larvae/pan
d) 200 larvae/pan, 50% Sw
e) 2 BR
f) 2 BR, 50% SW
g) 2 BR, 200 larvae/pan
h) 2 BR, 200 larvae/pan
50% SW


a)
b)
c)
d)
e)
f)
g)
h)


standard condition*
50% SW
200 larvae/pan
200 larvae/pan, 50% SW
2 BR
2 BR, 50% SW
2 BR, 200 larvae/pan
2 BR 200 larvae/pan,
50% SW


d
d
d
d
d
d
d
d


9
9
9
9
9
9
9
9


2.8
2.7
2.6
2.8
2.9
2.8
2.8
2.7


2.7
2.7
2.7
2.7
2.9
2.8
2.8
2.7



*


*
*

*


*

*
*


*



0.1
0.1
0.1
0.1
0.1
0.2
0.1
0.1


0.1
0.1
0.2
0.1
0.1
0.1
0.1
0.2


550
541
438
502
697
493
673
630


*
*
*



*


736
793
604
762
987
767
939
814


18.1
16.7
23.9
26.2
34.0
11.0
37.7
72.6


34.8
29.1
15.1
71.2
98.8
78.8
30.6
42.7


9.8
11.3
7.6
11.0
11.4
7.7
13.5
11.2


11.4
11.4
5.8
13.0
12.9
10.7
14.6
12.7


0.1
1.9
1.2
2.0
2.7
0.8
1.7
2.8


0.5
0.4
2.2
1.5
2.0
3.0
1.6
f 1.6


15.5
19.9
13.9
18.1
16.8
17.4
17.9
20.7


9.8
10.7
8.9
12.2 f
8.2
9.6
10.4
12.4


0.9
0.7
0.9
3.6
2.1
2.3
1.0
2.7


0.6
0.6
0.7
1.0
0.5
1.7
1.2
1.0


92.0
97.5
70.0
88.9
100.0
97.0
100.0
97.0


42.0
46.4
0.0
25.9
75.0
50.0
53.3
66.6


35.4 10.4
31.7 12.9
0.0
33.7 9.5
45.6 12.5
35.8 6.7
43.7 13.8
31.0 12.7






Table 6.2 (continued)


Aedes sollicitans
a) BR, 10% SW, 200
larvae/pan
b) 4 BR, 10% SW, 75
larvae/pan

a) BR, 10% SW, 200
larvae/pan
b) 4 BR, 10% SW, 75
larvae/pan


d 3.0 0.1 608 72

d 3.4 0.1 980 55


9 3.0 0.2 761 34


9 3.3 0.1 1249 62


8.4 0.1 16.9 2.1

11.4 1.1 14.8 0.8


7.4 0.4 7.3 0.8


15.4 2.5 11.5 0.4


*Standard rearing conditions: basic ration in 10% sea water with 75 larvae/pan at 270C under LD 12:12.
Variable factors: basic ration (BR); salinity of the sea water (SW); no. larvae/pan, 2 x basic ration (2 BR).
Basic ration adjusted to number of larve on mg/larva basis.
**Expression of autogeny was determined in non-mated females maintained for 4 days on a 10% sucrose solution,
modified from Nayar (1969).






In the pupal stage, where the rate of development is
controlled only by temperature, change in temperatures did not
have an appreciable effect on the adult characteristics (Nayar
1969).

Similarly, smaller adults of Ae. sollicitans with minimum
dry weights and lower percentages of lipid and glycogen were
obtained when 200 larvae/pan were reared on basic ration in
1/10 dilution of seawater; whereas the largest adults with
maximum dry weights and higher percentages of lipid and
glycogen were obtained when 75 larvae/pan were reared on 4x
basic ration in 1/10 dilution of seawater (Table 6.2) (Nayar
and Sauerman 1970a).

EFFECTS OF LARVAL AGGREGATION FORMATION ON ADULT
CHARACTERISTICS

The adults reared under standard conditions were
significantly smaller and lighter than adults reared under
temporarily crowded conditions with larvae showing aggrega-
tions, whether starved or fed during the temporary crowding
(Table 6.3). The percentages of energy reserves for adults
under standard conditions were also significantly lower than
in adults produced from larvae which showed aggregations
(Nayar and Sauerman 1968, 1970b). In Ae. taeniorhynchus only
73.6% of females under standard conditions had follicles in
stage III and none in stage V, four days after emergence,
whereas females from larvae which showed aggregations had
follicles both in stage III and V, showing enhanced autogeny
(Table 6.3).

Considering the ratios of dry weight to wing length
cubed, along with the ontogenetic timing, it became evident
that larvae that were excessively aggregated, either as
clusters or balls, produced larger adults with relatively low
dry weights (Nayar and Sauerman 1968, 1970b). It is suggested
that the adults produced under such conditions would likely
disperse more efficiently. This suggestion is also based on
the Provost's (1957) studies, where larvae were extensively
crowded in their late third and fourth instars. Possibly
these conditions produced adults more capable of exhibiting
migratory behavior.

SURVIVAL OF UNFED ADULTS

In the laboratory, the adults of these species do not
feed and/or fly well for several hours after emergence. If
the adults are not allowed to feed, they can survive and fly
in a diurnal rhythm for 2 to 4 days after emergence, depending
upon the original level of energy reserves (Nayar and Sauerman
1971a). During survival, both glycogen and triglyceride
reserves decline in proportion to the amount present up to 50%


54






survival time, so that the logarithm of the reserves plotted
as a function of time yields a straight line (Nayar and Pierce
1977). The survival of unfed adults is also dependent on
temperature. The lower the temperature, the longer the energy
reserves will last. When Ae. sollicitans were maintained at
different temperatures on water, the females survived from 4.5
days at 300C to 27 days at 100C (Table 6.4) (Van Handel
1973). In the laboratory, unfed Ae. taeniorhynchus and Ae.
sollicitans have enough energy soon after emergence to fly for
several hours on a flight mill, utilizing glycogen as a main
source of flight energy (Nayar and Van Handel 1971). To
survive for any longer periods the adults must feed.

SURVIVAL OF ADULTS AFTER FEEDING

Adult mosquitoes feed primarily on sugars, usually plant
nectars, with females also feeding on vertebrate blood
(Clements 1963, Nayar and Sauerman 1975a, 1975b). Sugars are
utilized as the main source of nutrition and energy needed for
the considerable amount of flight by Ae. taeniorhynchus and
Ae. sollicitans. Some females of Ae. taeniorhynchus may
produce a batch of autogenous eggs, although generally blood
is utilized for production of the initial and all subsequent
egg batches.

Nectar and sugar-feeding: On the east and west coasts of
Florida, Haeger (1955) observed Ae. taeniorhynchus in the
field, feeding on the extrafloral glands on the petioles of
buttonwood (Conocarpus erectus); on flowers of black
mangrove (Avicennia nitida), saw palmetto (Serenoa repens),
cabbage palm (Sabal palmetto), and sea grape (Coccolobus
uvifera); and on the aphid honey-dew deposited on the leaves
of spanish needle (Bidens sp.).

Bidlingmayer and Hem (1973) used the cold anthrone method
of Van Handel (1972a) to test for the presence of fructose in
field-caught Ae. taeniorhynchus adults collected by portable
power aspirators and females collected by suction traps. In a
maple swamp about 10 miles west of the Atlantic coast, 65 to
87% were positive for fructose, indicating that they had
recently fed on nectar. In suction trap collections made
adjacent to a salt marsh, the percentage of individuals with
fructose ranged from 9 to 65% during different months of the
year. Substantially more females with fructose were collected
during spring and fall months than during summer, with fewest
in winter months.

Adult Ae. taeniorhynchus can live up to 2 months in the
laboratory on a 10% sucrose solution provided ad lib. as this
apparently satisfies all necessary nutritional requirements
for survival (Nayar and Sauerman 1971a). When newly emerged
Ae. taeniorhynchus females were fed on either a 5%, 10%, or


55








Table 6.3.


The adult characteristics of Aedes taeniorhynchus (Vero Beach strain) and
Aedes sollicitans (Vero Beach strain) and expression of autogeny of Aedes
taeniorhnchus after emergence*, from larvae reared under differing conditions.
The data are expressed as the mean standard deviation and the mean of four
samples of five individuals per sample.


Energy Reserves
Weight, Percentage of
Rearing Wing Length Mean Dry dry body weight
Conditions Sex (mm) ( g/adult) Lipid Glycogen


Aedes taeniorhynchus

Standard** conditions
Group A***
Group B****

Standard conditions
Group A
Group B

Aedes sollicitans

Standard condition
Group A**
Group B***


d
d
d

9
9
9


d
d
d


2.63
2.82
2.74

2.71
2.86
2.85



3.18
3.20
3.02


0.08
0.05
0.08

0.07
0.07
0.08



0.06
0.05
0.06


428
580
443

559
737
622


13.6
73.0
11.60

93.20
92.4
19.80


588 14.0
628 17.6
578 13.2


8.29
11.98
9.14

8.50
9.71
10.62



8.74
8.74
8.98


1.35
2.51
0.94

2.23
4.56
1.84



0.79
1.03
1.09


10.08
13.43
10.46

8.58
6.67
7.82



13.74
10.11
10.88


1.71
0.54
0.61

0.95
2.07
0.31



1.22
1.01
1.05


Ul
(^




-11 lk qP - qW Mr V 9 1 - 10 qW


Table 6.3 (continued)

Standard condition
Group A**
Group B***


3.05 0.07
3.09 0.08
2.99 0.06


722 f 15.2
812 13.2
674 11.2


6.44 0.91
8.93 + 0.83
7.36 0.82


6.90 f 0.81
6.00 0.71
5.79 0.40


*State of autogeny
for 4 days on 10%


was determined in non-mated female Ae. taeniorhynchus maintained
sucrose solution.
% females with % females Average number
stage III or with stage of stage V
above follicles V follicles follicle/female


73.6
70
57.1


38
38.4


37.5 f 5.03
29.00 5.00


**Standard rearing condition: 400 larvae were reared in a pan containing 350 mL of
10% sea water at 270C under LD 12:12, with fee schedule: day 1 320 mg Brewer's
yeast, day 2 40 mg liver powder, day 3-7 160 mg Brewer's yeast daily.
***Group A: 2000 larvae from five pans were temporarily crowded in one pan with 500 mL
of 10% sea water for 8 hr daily during the light period of LD 12:12 cycle and fed
320 mg of Brewer's yeast.
****Group B: 2000 larvae from five pans were temporarily crowded in one pan with 500 mL
of 10% sea water for 8 hours daily during the light period of LD 12:12 cycle and
and starved.


Ln
_1


4 % N'- 6-








Table 6.4 Mortality and caloric expenditures in adult Aedes sollicitans starving
after emergence.*

Males Females
Caloric Caloric
Temperature Mortality** Expenditure*** Mortality** Expenditure***
(C) HR S.E. HR HR S.E. HR

10 430 15 240 650 12 280
15 264 5 145 400 12 170
20 180 6 96 280 5 120
25 132 3 65 200 3 90
30 87 4 48 108 3 60

*Modified from Van Handel (1973).
**Time in which 50% of the population had died.
***Time in which the net caloric content was reduced to 50% of that
present at emergence.






25% solution of sucrose in a potometer (made from a glass tube
20 cm long and 0.4 cm o.d., bent into a J-shape, one arm 4 cm
long and the other arm 13 cm long), the volume imbibed per
female per day was greatest for the first 5 days after
emergence on the 5% sucrose solution, and least for the same
period on the 25% sucrose solution (Nayar and Sauerman
1974). However, the sugar intake was substantially greater on
25% than on 5% sucrose solution. Both volume and caloric
intake declined considerably after the fifth day, and remained
roughly constant for the next 4 weeks. The total intake of
sucrose over a period of 37 days indicated that concentration
and volume intake were inversely correlated, whereas caloric
intake was directly related to concentration (Nayar and
Sauerman 1974). There was no difference in mortality of
females by 37 days age on all three concentrations;
approximately 20% died in each of the groups.

When sugar is transferred from the crop to the gut,
absorption through the gut wall into the hemolymph takes place
so rapidly that at no time is an appreciable amount of sugar
found in the gut. Sucrose is split by a gut enzyme into
glucose and fructose. Absorbed glucose and fructose are
either immediately used for energy, or converted into three
products: (1) trehalose, a disaccharide that consists of two
molecules of glucose, and is the mosquito's own blood sugar,
(2) glycogen, a polysaccharide, consisting of a long chain of
glucose molecules, and (3) common fat (triglycerides). The
main fuels are the sugar (stored in the crop), glycogen, and
triglyceride stored in the fat body.

At emergence, male and female Ae. sollicitans and Ae.
taeniorhynchus contain approximately equal, small amounts of
fat. When maintained on sugar, the fat content of the female
rises steadily for about 7 days, whereas during the same time,
the fat nearly disappears from the male. After 7 days, the
amount of fat (triglycerides) may be 50 times as great in the
female as in the male (Van Handel and Lum 1961).
Consequently, the well-fed female mosquito can survive a long
time without the necessity to have food constantly
available. When the unfed female Ae. sollicitans takes a
sugar meal of less than 0.25 mg, it is used only for energy.
Sugar meals between 0.25 and 0.50 mg allow deposition of
glycogen. When the sugar meal exceeds 0.5 mg, some fat is
also deposited. With increasing sugar meals, the amount of
fat increases, but not the amount of glycogen (Van Handel
1965). The decision whether sugar will be used for fat or
for glycogen accumulation is controlled by certain cells in
the brain. In Ae. sollicitans and Ae. taeniorhynchus, two
groups of medial neurosecretory cells (MNC), 12 to 15 cells
each, lie in a cluster on either side of the midline of the
protocerebrum. They are easily distinguishable by their
bluish appearance. When these mosquitoes are fed on 1 mg


59






sugar, the fat (triglyceride) will largely exceed the glycogen
level. However, when the MNC are surgically removed before
the sugar meal, the glycogen will largely exceed the fat level
(Table 6.5) (Van Handel and Lea 1965).

Table 6.5. Effect of removal of medial neurosecretory cells
(MNC) on net increases of glycogen and tri-
glycerides, 48 hours after they were fed 4
cal (1 ll, 50 percent) of sugar.*

Net Increase S.E.
(cal/mosquito)

N Glycogen Triglyceride

Aedes taeniorhynchus

Intact controls 17 0.20 .03 1.3 .09
MNC removed 14 1.1 .09 0.34 .03

Aedes sollicitans

Intact controls 5 0.50 .10 1.20 .20
MNC removed 5 1.40 .20 0.62 .07

*Modified from Van Handel and Lea (1965).

Sugar metabolism for survival by Ae. taeniorhynchus
follows a similar pattern (Nayar and Sauerman 1975a). How
often females feed on sugar in the field is unknown. The
sugar content of several flower nectars, collected from a
large variety of flowering plants in Florida, ranged between
10 and 20% (C.W. Hansen, unpublished).

Not all sugars are metabolized equally well. Nayar and
Sauerman (1971b) showed that sorbose acted solely as a
phagostimulant and was not metabolized when fed alone or with
other sugars. Survival in Ae. taeniorhynchus females was
greatest on most hexoses, disaccharides, some trisaccharides
and polysaccharides, and some sugar-alcohols. Some other
carbohydrates including pentoses and sugar alcohols, did not
support survival more than distilled water. Twenty-four hours
after feeding, glycogen accumulation was proportional to the
increase in survival times of adults. Adults fed those
carbohydrates which did not increase survival better than
water did not accumulate glycogen.

Quantitative analyses for fat, glycogen, and sugar in
field populations are not available, but distribution of
available calories in a field population of Ae. taenior-
rhynchus, collected in suction traps and analyzed by the


60






difference in bichromate value between the collected
individuals and a starved population, ranged from 0 to 6
calories (Van Handel 1972a).

Effects of temperature: In the laboratory, Ae.
taeniorhynchus adults obtained from larvae reared at constant
temperatures of 220C, 270C and 320C and maintained ad lib. on
a 10% sucrose solution, at the same constant temperatures and
70% to 75% RH, show temperature dependence in the 50% survival
times. The 50% survival times for males are 12 days at 32C
and 21.9 days at 22C, with a Q10 value of 1.8, and for
females are 22 days at 320C and 41.2 days at 220C, with a Q10
value of 1.9, showing a distinct temperature dependence (Nayar
1972).

Metabolism of the blood meal: Aedes taeniorhynchus and
Ae. sollicitans females ingested ca. 2.5 and 3.0 times their
mean unfed wet weights, respectively, of vertebrate blood in a
meal. In terms of survival efficiency, these females survived
68.5 and 44.0 hr/cal (16.4 and 10.5 hr/J) respectively of
blood (Nayar and Sauerman 1975b). Soon after blood feeding,
the anal discharge of clear fluid and undigested blood was
observed, indicating that not all the ingested blood was
utilized for either survival or oocyte maturation. Soon after
ingestion some of the blood was utilized for synthesis of
glycogen and triglyceride reserves, which could be used for
survival by the female. Part of the energy reserves
synthesized from a blood meal prolonged survival of otherwise
unfed females for 8 days more than the starved females, and
the remainder of the reserves were stored as yolk in matured
oocytes (Nayar and Sauerman 1975b).

The studies on adult nutrition and metabolism of salt
marsh mosquitoes show that the use to which the nectar
meal and the blood meal are put is regulated by a
sophisticated endocrine control system, and that wide
fluctuations of temperature are easily tolerated. Unlike
other biting flies, the female mosquito stores a large amount
of fat that is used for longevity, and not for flight. The
parsimonious management of food resources explains why the
female mosquito is such a persistent pest and efficient vector
of pathogens.

Survival of adults in the field: In the field it is
impossible to calculate the 50% survival time of mosquitoes by
direct observation, so other methods must be used; e.g., the
survival rates can be estimated from an analysis of mark-
release data (Service 1976). No experiments have been
conducted to calculate survival rates of Ae. taeniorhynchus.
However, after reconsideration of the number of marked Ae.
taeniorhynchus females recaptured during dispersal experiments
by Provost (1952) and Bidlingmayer and Schoof (1957), it was


61






evident that the number of recaptured females after each
release increased for 2 or 3 days following release and then
declined rapidly with each successive day. When these data
were plotted on a semilog scale, most of the points from day 2
or 3 to day 9 fell more or less along straight lines. This
indicated that the daily survival rate was constant for
females 2 or 3 days after each release. Following Gillies'
(1961) suggestion that in order to calculate the survival
rate, the first 2 to 3 days' recoveries should be excluded,
the daily survival rate (p) was then calculated from the
frequency of the numbers caught on each subsequent day
starting after maximum numbers of adults of each sex were
captured on any particular day; i.e., the maximum number was
set to 100% on the second or third day after release. The
regression coefficients ( B) for the logarithm of the numbers
of females captured by Provost (1952) and Bidlingmayer and
Schoof (1957) are -0.114 and -0.091, respectively; and the
corresponding daily survival values are 0.77 and 0.81,
respectively. These studies thus indicated that in late
August and early September, when both of these experiments
were conducted, the daily survival rate of Ae. taeniorhynchus
females at Sanibel Island in 1951 was 77% and at Savannah,
Georgia, in 1954 was 81%.

Correlation of the daily survival rates with vector
potentials: Since daily survival rates of 77% to 81% were
observed in Ae. taeniorhynchus, it is feasible that higher
daily survival rates may occur in spring, early summer, and
late fall in Florida and Georgia. Using the analysis of the
relationship between the daily survival rates, blood-feeding,
and oviposition described for Culex nigripalpus by Nayar
(1982), 3% to 7% of the brood are capable of living more than
13 days after emergence during the summer months. Thus at 77%
to 81% or higher survival rates in early summer or late fall,
the survival of 10% or more adult Ae. taeniorhynchus is
possible beyond 14 or more days after emergence.

Survival for 13 to 19 days with two or three blood
feedings is necessary for the transmission of viruses and
parasites (Nayar 1982), which require 12 to 15 days of
incubation in the mosquito (Sudia and Chamberlain 1964, Young
et al. 1977, Nayar and Sauerman 1975c). On these grounds, Ae.
taeniorhynchus can be considered an excellent vector of some
of the important viruses and filariid worms in Florida.

ADULT EXCRETION

The main excretory organs in the adult stage are the
Malpighian tubules and the rectum. The Malpighian tubules
show some interesting differences in their excretory function
between larvae and adults. (1) The tubule cells do not
undergo histolysis during pupation, and the adults and larvae


62






have identical cell types (Bradley 1983). However, Maddrell &
Phillips (1978) reported that larvae reared in high SO4 water
show induced transport of SO4 yet adults reared from these
larvae do not. Therefore, although apparently the same cells
are involved, this physiological capacity has been lost in the
larval-adult metamorphosis. (2) Probably the greatest osmo-
regulatory challenge facing the adult is the post-bloodmeal
diuresis. In Ae. taeniorhynchus, this rapid diuresis is
observed and is apparently under hormonal control since the
Malpighian tubules in vitro can be stimulated by a homogenate
of the head of the insect, 5-hydroxytryptamine (5-HT) or
cyclic adenosine monophosphate (cAMP). Larval Malpighian
tubules will respond to 5-HT by increasing the rate of
secretion, but the secreted fluid remains K+-rich (Bradley
1983). In adults, the tubules respond to all the above
stimuli by increasing the secretary rate and increasing the
Na+/K+ ratio in the secreted fluid (Bradley 1983). This is,
of course, beneficial since the fluid they must dump is the
Na+-rich plasma associated with the ingested food. Although
this phenomenon is observed in all adult tubules, it is more
marked in the tubules of female mosquitoes (Maddrell 1977).

Unlike the larvae, the adults generally face a dry,
desiccating environment. In the adult a modification to a
papillate rectum (Clements 1963) typical of adult Diptera
occurs. Although its function has not been studied in Ae.
taeniorhynchus, studies on other Diptera indicate that
hyperosmotic excreta are produced by water resorption in the
rectum (Gupta et al. 1976).


63






REFERENCES CITED


Bidlingmayer, W. L., and D. G. Hem.
1973. Sugar feeding by Florida mosquitoes. Mosquito
News 33: 535-538.
Bidlingmayer, W. L., and H. F. Schoof.
1957. The dispersal characteristics of the salt-marsh
mosquito, Aedes taeniorhynchus (Wiedemann), near
Savannah, Georgia. Mosquito News 17: 202-212.
Bradley, T. J.
1983. The excretory system: structure and physiology.
In Comprehensive Insect Physiology, Biochemistry
and Pharmacology, Vol. 4. G. A. Kerkut and L. I.
Gilbert, eds., Pergamon Press, London.
Clements, A. N.
1963. The physiology of mosquitoes. The Macmillan Co.,
New York. 393 pp.
Gillies, M. T.
1961. Studies on the dispersal and survival of Anopheles
gambiae Giles in East Africa, by means of marking
and release experiments. Bull. Ent. Res.
52: 99-127.
Gupta, B. L., T. A. Hall, S. H. P. Maddrell, and R. B.
Moreton.
1976. Distribution of ions in a fluid-transporting
epithelium determined by electron-probe x-ray
microanalysis. Nature 264: 284-287.
Haeger, J. S.
1955. The non-blood feeding habits of Aedes
taeniorhynchus (Diptera: (Culicide) on Sanibel
Island, Florida. Mosquito News 15: 21-26.
Lea, A. 0.
1964. Studies on the dietary and endocrine regulation of
autogenous reproduction in Aedes taeniorhynchus
(Wied.). J. Med. Ent. 1: 40-44.
Maddrell, S. H. P.
1977. Insect Malpighian tubules. p. 541-570. In
Transport of ions and water in Animals. B. L.
Gupta, R. B. Moreton, J. L. Oschman and B. L.
Wall, eds., Academic Press, New York.
Maddrell, S. H. P., and J. E. Phillips
1978. Induction of sulphate transport and hormonal
control of fluid secretion by Malpighian tubules
of larvae of the mosquito Aedes taeniorhynchus.
J. Exp. Biol. 72: 181-202.
Nayar, J. K.
1966. A method of rearing salt-marsh mosquito larvae in
a defined sterile medium. Ann. Ent. Soc. Am. 59:
1283-1285.


64






1967. The pupation rhythm in Aedes taeniorhynchus
(Diptera: Culicidae). II. Ontogenetic timing,
rate of development and endogenous diurnal rhythm
of pupation. Ann. Ent. Soc. Am. 60:
946-971.
1969. Effects of larval and pupal environmental factors
on biological status of adults at emergence in
Aedes taeniorhynchus. Bull. Ent. Res. 58:
811-827.
1972. Effects of constant and fluctuating temperatures on
life span of Aedes taeniorhynchus adults. J.
Insect Physiol. 18: 1303-1313.
1982. Bionomics and physiology of Culex nigripalpus
(Diptera Culicidae) of Florida: An important
vector of diseases. Bulletin 827 (technical).
Florida Agricultural Experiment Stations, IFAS,
Univ. of Florida, Gainesville. 73 pp.
Nayar, J. K., and P. A. Pierce.
1977. Utilization of energy reserves during survival
after emergence in Florida mosquitoes. J. Med.
Ent. 14: 54-59.
Nayar, J. K., and D. M. Sauerman, Jr.
1968. Larval aggregation formation and population
density interrelations in Aedes taeniorhynchus,
their effects on pupal ecdysis and adult charac-
teristic at emergence. Entomologia Exp. Appl.
11: 423-442.
1970a. A comparative study of growth and development in
Florida mosquitoes. Part 2. Effects of larval
nurture on adult characteristics at emergence.
J. Med. Ent. 7: 235-241.
1970b. A comparative study of growth and development in
Florida mosquitoes. Part 3. Effects of temporary
crowding on larval aggregation formation, pupal
ecdysis and adult characteristics at emergence.
J. Med. Ent. 7: 521-528.
1971a. The effects of diet on lifespan, fecundity and
flight potential of Aedes taeniorhynchus adults.
J. Med. Ent. 8: 506-513.
1971b Physiological effects of carbohydrates on
survival, metabolism and flight potential of
female Aedes taeniorhynchus. J. Insect Physiol.
17: 2221-2223.
1974. Long-term regulation of sucrose intake by the
female mosquito, Aedes taeniorhynchus. J. Insect
Physiol. 20: 1203-1208.
1975a. The effects of nutrition on survival and fecundity
in Florida mosquitoes. Part 1. Utilization of
sugar for survival. J. Med. Ent. 12: 92-98.


65






1975b. The effects of nutrition on survival and fecundity
in Florida mosquitoes. Part 2. Utilization of a
blood meal for survival. J. Med. Ent.
12: 99-103.
1975c. Physiological basis of host susceptibility of
Florida mosquitoes Dirofilaria immitis. J. Insect
Physiol. 21: 1965-1975.
Nayar, J. K., and E. Van Handel.
1971. The fuel for sustained mosquito flight. J. Insect
Physiol. 17: 471-481.
Provost, M. W.
1952. The dispersal of Aedes taeniorhynchus. 1.
Preliminary studies. Mosquito News 12: 141-156.
1957. The dispersal of Aedes taeniorhynchus II. The
second experiment. Mosquito News 17: 233-247.
Service, M. W.
1976. Mosquito ecology (field sampling methods).
Halstead Press, John Wiley & Sons, New York.
583 pp.
Sudia, W. D., and R. W. Chamberlain.
1964. Experimental infection of Culex nigripalpus
Theobald with the virus of St. Louis
Encephalitis. Am. J. Trop. Med. Hyg. 13:
469-471.
Van Handel, E.
1965. The obese mosquito. J. Physiol. 181: 478-486.
1972a. The detection of nectar in mosquitoes. Mosquito
News 32: 458.
1972b. Simple biological and chemical methods to
determine the caloric reserves of mosquitoes.
Mosquito News 32: 589-591.
1973. Temperature dependence of caloric expenditure and
mortality in the starving mosquito. Comp.
Biochem. Physiol. 44: 1321-1323.
Van Handel, E., and A. 0. Lea.
1965. Medial neurosecretory cells as regulators of
glycogen and triglyceride synthesis. Science
149: 298-300.
Van Handel, E., and P. T. M. Lum.
1961. Sex as regulator of triglyceride metabolism in the
mosquito. Science 134: 1979-1980.
Young, M. D., J. K. Nayar, and D. J. Forrester.
1977. Mosquito transmission of wild turkey malaria,
Plasmodium hermani. J. Wildlife Dis. 13: 168-169.


66






CHAPTER 7


FIELD FLIGHT BEHAVIOR

A. SWARMING: E. T. Nielsen

Many people know that male mosquitoes form swarms in the
evening, but as the terms for this sometimes are used
haphazardly, it is useful to begin with a definition: swarming
is the habit of some male insects, especially mosquitoes, to
perform a ritual flight within a limited space (Fig. 7.1),
repeated at a certain time every dusk and usually also dawn,
from the time the male is a few days old till he dies. He
will perform these special movements the same way whether he
is alone or joined by a multitude of other males.


Fig. 7.1. Aedes taeniorhynchus swarming over black mangrove
(Avicennia germinans). Photo by J. S. Haeger.

Females may teem around a vertebrate host, and that is
sometimes called swarming--incorrectly, for these flights are
clearly aimed at the victim.


67






The place selected for the swarming is used by genera-
tions of males. In some species it is over a contrasting
light and dark area on the ground; in others, such as Aedes
taeniorhynchus, it is over the top of a bush or a small tree,
forming what is called a top-swarm.

Swarming usually begins with a single male performing the
ritual flight, but others soon join him. The moment of
initial flight depends mostly on a certain kind of illumina-
tion associated with twilight. Civil twilight is between sun-
set and the moment when the center of the sun is 60 below the
horizon. Apart from atmospheric disturbances and moonlight,
the illumination depends solely on the altitude of the sun; on
a clear night, illumination is 398 lux at sunset and 36 lux at
the end of twilight. Twilight period is the moment when the
stars of first magnitude appear, and the flowers seem to lose
their colors. It is the moment when it gets too dark to work
outdoors without artificial light. The morning twilight is a
corresponding period.

In Florida twilight lasts between 23 and 27 minutes,
depending on the season. Aedes taeniorhynchus males begin
swarming when the twilight period is half over, and swarming
lasts about 25 minutes (Fig. 7.2). Thus when the stars
appear, there is still 10 to 15 minutes of swarming time left,
though it gets too dark to see the last part of the flight
performance. An ordinary flashlight may disturb the insects,
but an electronic flash, as used in photography, clearly
reveals the swarmers without causing disturbance. The swarms
are very sensitive to sound; the honking of a distant auto-
mobile horn may disrupt the swarms. Once a swarm was observed
in a strange rhythmical tremor; careful listening revealed
that it was caused by the sound of distant hammering. Talking
or singing will disperse the swarm. Morning swarms begin
before the morning twilight and end before sunrise.

The times I have given for swarming refer to ideal
conditions: clear, calm weather with a temperature of about
200C to 240C. Both the beginning and the end of swarming
depends on the illumination, so on dark, cloudy evenings the
flight period is advanced, especially the beginning of the
swarming. High temperature may delay the activity and so may
high winds. Gentle winds have another effect: swarming is
not performed above tree-top level but takes place on the lee
side. Even the slightest wind will cause the swarmers to fly
with their heads against the wind. This reaction is seen even
when the breeze cannot be readily detected. Very strong winds
and heavy rain may completely impede swarming.

Though swarms last 20 to 25 minutes, individual males fly
less than a couple of minutes. It is difficult to see the
departures and arrivals of the swarmers; but if the whole


68






















I -


SS SWI tw SWII



Fig. 7.2 Diagram showing the relationship between the
swarming of Aedes taeniorhynchus (above) and the illumi-
nation in the evenings. SS is the sunset, and from left
to right it gets darker. The twilight ends at tw. Swarm-
ing starts at SWI and ends at SWII.

swarm is caught, it will, after a few minutes, be replaced by
a similar swarm. Once a brood of Ae. taeniorhynchus was
observed emerging and at the same time a large number of
dragonflies appeared. As soon as a swarm formed, a couple
of dragonflies criss-crossed the swarm, which promptly
disappeared. This was repeated again and again as soon as new
males formed the swarm again.

If all the males during the whole period of swarming are
caught, the following evening there will not be swarming at
that place. This, and experiments with marked individuals,
have shown that a male ordinarily takes part in the same swarm
every night; even if there are other swarms close by, there is
little exchange of individuals.

The continued succession of individuals in the swarm is
explained by the assumption that there are individual
differences in sensitivity to illumination, which triggers the
swarming activity; some males start at the light prevailing at
10 minutes after sunset, others when it is a little darker.
The assumption is supported by experiments with marked
individuals which showed that those swarming early one evening
also did so the following evening, and the same was the case
with late swarmers.


69






It seems justified to assume that each male swarms
evenings and mornings at the same place at the same
illumination and thus at the same time in relation to
twilight.

Why do mosquito males swarm? We do not know. For a long
time it was thought that swarming was a sexual behavior.
Behind the concept of "mating swarms" was the assumption that
the males have only one function: to inseminate the females.
So, the reasoning went, whatever males were doing must have
sexual significance. Since copulation has to be initiated in
flight, and since males were rarely seen except in swarms, the
function of the swarm was thought to be to attract females by
the humming of the swarm.

This explanation is wrong. In most species, and Ae.
taeniorhynchus is one of them, direct observations show that
matings rarely occur in the swarms. Furthermore, females are
not attracted by the humming of the males; on the contrary,
males are attracted to the flight tone of the females. In
some species matings may occur frequently in swarms; e.g.,
Culex pipiens; but in others practically never. In Ae.
taeniorhynchus it happens sometimes, probably when there are
old males from an earlier brood swarming at the time when new,
virgin females appear. In isolated broods the males do not
begin to swarm until after the females have mated.


70






SUGGESTED REFERENCES


Nielsen, E.
1950.

Nielsen, E.
1960.

Nielsen, E.
1953.

Nielsen, E.
1963.

Nielsen, H.
1963.


T., and Hans Geve.
Studies on the swarming habits of mosquitoes and
other Nematocera. Bull. Ent. Res. 41: 227-258.
T., and J. S. Haeger.
Swarming and mating in mosquitoes. Misc. Publ.
Ent. Soc. Am. 1: 71-95.
T., and A. T. Nielsen.
Field observations on the habits of Aedes
taeniorhynchus. Ecology 34: 141-156.
T., and H. T. Nielsen.
The swarming habits of some Danish mosquitoes.
Ent. Medd. 32: 99-170.
T. and E. T. Nielsen.
Swarming of mosquitoes. Laboratory experiments
under controlled conditions. Ent. Exp. Appl. 5:
14-32.


71






B. MIGRATORY FLIGHT: J. S. Haeger


Migration in the mosquito Aedes taeniorhynchus is similar
to other insect migrations, but special capture techniques are
required for studying the flight movements. Detailed
observations have been made on the first day of adult life
prior to and during the exodus from the emergence site
(Provost 1952, 1957, 1960, Nielsen 1958, 1964, Haeger 1960,
Pausch and Provost 1965).

Mosquito migration is a non-appetential type flight
(Provost 1952), implying nonstop flight away from the home
range, the area of marsh in which all normal activities of
adult life take place (Nielsen 1964). Mosquito migrations,
like that of other insects, take on an undirectional pattern,
and are always associated with a population outbreak of
millions of individuals (Kennedy 1961). Dispersal by
migration follows an initial exodus, which is an end in itself
(Provost 1952, 1953). Appetential flight dispersal occupies
future activities connected with food, shelter, oviposition,
etc., within the new range (see this Chapter, Section C).

Provost (1952) showed that Ae. taeniorhynchus migrate in
response to types of topography in the landscape and under the
influence of meteorological conditions such as wind speed and
direction. Migration in Aedes sollicitans has not been
observed in Florida. The following description of the exodus
and migration refers only to Ae. taeniorhynchus, and generally
reflect my personal observations.

Examples of premigration behavior

A. Sanibel Island, May 1953. Several million adults had
emerged during the night and early morning hours and were
still emerging or resting quietly (at 0830) on pickle weed,
Batis maritimum, on aerial roots and small trees of black man-
groves, Avicennia germinans (Fig. 7.3a) or among sedges (Fig.
7.3b). The black mangrove trees were in full bloom, and many
of the young adults were engorging on the nectar, even in the
morning. By midafternoon, nectar feeding increased and counts
of the sexes feeding on flowers showed that twice as many
males were feeding as females. Sometimes two or three would
be feeding on a single flower (Haeger (1955).

At 20 -in before sunset, adults of both sexes began an
ascent into the taller trees, accompanied by short hovering
flights from one twig or leaf to another until the trees were
covered from the ground up to 24 ft (near tops of the
trees). At 4 min past sunset the sex ratio of nectar feeding
individuals had changed to 5 females to every 2 males.


72






The onset of the departure (exodus) normally occurs after
sunset, but under very dark clouds it can begin before sunset,
if the young adults are over 8 or 9 hr old since emergence and
air temperature has averaged about 280C. This suggests that a
threshold of light must trigger the exodus (Nielsen 1958).
Nectar-filled adults left their resting places and became air-
borne at 14 min past sunset, and flew towards the brightest
part of the sky. Then between 18 and 25 min past sunset even
larger waves left, probably by age groups (Nielsen 1958;
Haeger 1960; Pausch and Provost 1965).

Pairing (mating) was observed between 26 and 39 min past
sunset, and 75 percent of all females leaving the branch of a
tree under observation were caught by males that were also
leaving from the same area (no swarms were present). These
pairings occurred after very short flights of 3 to 12 inches
of upward flight and ended in end-to-end separation (Haeger
1960). This pairing, however, may not necessarily have
resulted in many females being inseminated. Later, Edman et
al. (1972) found during a large field experiment that
insemination most often occurred 30-40 hr after emergence.

On the second day of emergence this brood showed a sex
ratio of 50 males:50 females during the time of feeding on
flower nectar prior to sunset. The exodus started 45 min
earlier than the previous day because of very dark rain clouds
obscuring the sunset. By climbing a sturdy mangrove tree it
was possible to observe, at a level of 21 ft above the marsh,
that very large swarms were undulating above the tree tops.
Males in these swarms were of an estimated age of 42 hr after
the first day's emergence of this brood.

B. Vero Beach, August 1955. A large brood consisted of
about 60,000,000 pupae (estimated by measuring the rafts of
pupae and counting aliquots taken from dipping collections
from several of these rafts). This brood emerged over a
three-day period, and on the third day about 10,000,000 adults
emerged.

The exodus observed each day was spectacular, but no
mating was observed, and little nectar feeding took place
because few flowers were blooming close by. Figure 7.4 shows
how the exodus proceeded. The adults flew up in mass, and as
the adult mosquitoes reached the top of the trees, they all
flew into a light breeze (velocity less than 1 mile/hr). On
the third night an early exodus was observed, as described at
Sanibel, when a dark cloud caused a premature drop in light
level. These two observations on mosquitoes taking flight
prematurely agree with observations of Nielsen (1958) that
certain levels of light trigger spontaneous flight.


73








































Fig. 7.3a. Adult Aedes taeniorhynchus emerging from black mangrove, showing
how extensive the large pupal rafts were at emergence time. The pneumato-
phores are lined with new adults.






































Fig. 7.3b. A close-up picture of Aedes taeniorhynchus resting at an emergence
site in early afternoon.









































Fig. 7.4. Adult Aedes taeniorhynchus during exodus. All migrants are flying
in one direction, in this case upwind. Photo by J. S. Haeger.






Migration


The migratory flight described was seen at Vero Beach,
Florida (example B, preceding). After the exodus was complete
in the immediate area, the migrants from the northern parts
of the marsh continued to fly overhead in a thick stream,
undulating over the tree tops, dipping down a little between
trees (Fig. 7.5). This flight was following along the
juncture where the high marsh and the upland live oak and
sabal palm hammock join. After about 5 min the mosquitoes had
all passed by. It was now quiet, and no mosquitoes could be
seen or heard; there were no females biting, as all were too
young (Haeger 1960).

Although the initial stages of migration were observed,
the complete flight patterns and the distances flown on this
maiden flight were unknown. The great importance of metero-
logical and topographical factors was clearly demonstrated
during these observations.

Provost (1952, 1957) showed that by marking larvae
with 32P radioisotope the captured adults could be separated
from collections made at various distances away from the
emergence site. Two such experiments were conducted at
Sanibel Island in which some female recoveries were made at
16-20 miles, while most males were recovered only up to two
miles from the exodus site during three-week period after
exodus. The direction flown in these cases was downwind and
along the shoreline of the islands lying north and northwest
of Sanibel. Winds were generally quite strong (5-10 miles/hr)
during the evenings when each exodus took place. Since light
traps (New Jersey) were the best method of recovering the
adults, about 50 of these traps were run each night at
measured mile intervals on several radii. Only on the third
night were marked individuals first attracted to the light
traps, the first captures occurring 2 or 3 days after the
migratory flight was presumed to be over (Provost 1952).
About 50% of marked females caught were recovered from traps
located over 5 miles from the exodus site. The light traps
were run each night for 3 weeks to compile a picture of the
mosquito dispersal pattern.

In later experiments with other recovery methods, sticky
nets placed on poles and nylon nets 2 meters square, made with
detachable tails 2 meters long, were placed at two levels
between double vertical poles (these could be raised and
lowered by pulleys) located 75-100 ft from the emergence site
at the four cardinal points. This configuration gave the
direction and the elevation at which the mosquitoes were
flying on take-off (Provost 1960).


77













S WIND < 0.5mph N






0 *BLACK L
MANGROVE L

-,- I-

Fig. 7.5. Migratory flight of Aedes taeniorhynchus (upwind) when wind was less
than 0.5 miles per hour. Millions of mosquitoes were observed at this exodus.






Not all broods of Ae. taeniorhyncFus migrate, as shown in
two mark-release experiments using P at Savannah, Georgia
(Bidlingmayer and Schoof 1957, Elmore and Schoof 1963). These
adults emerged with low energy reserves and at a location and
time when nectar was unavailable, therefore, they flew only a
very short distance from the emergence site.


79






REFERENCES CITED


Bidlingmayer, W. L., and H. F. Schoof
1957. The dispersal characteristics of the salt marsh
mosquito, Aedes taeniorhynchus (Wiedemann), near
Savannah, Georgia. Mosquito News 17: 202-212.
Edman, J. D., J. S. Haeger, W. L. Bidlingmayer, R. P. Dow, J.
K. Nayar, and M. W. Provost.
1972. Sexual behavior of mosquitoes. 4. Field
observations on mating and insemination of marked
broods of Aedes taeniorhynchus. Ann. Ent. Soc.
Am. 65: 848-852.
Elmore, C. M., and H. F. Schoof.
1963. Dispersal of Aedes taeniorhynchus Wied. near
Savannah, Georgia. Mosquito News 23: 1-7.
Haeger, J. S.
1955. The non-blood feeding habits of Aedes
taeniorhynchus (Diptera, Culicidae) on Sanibel
Island, Florida. Mosquito News 15: 21-26.
1960. Behavior preceding migration in the salt marsh
mosquito, Aedes taeniorhynchus. Mosquito News
20: 136-147.


Kennedy, J.
1961.

Nielsen, E.


Pausc



Provo


S.
A turning point in the study of insect
migration. Nature 189: 785-791.
T.


1958. The initial stage of migration in salt marsh
mosquitoes. Bull. Ent. Res. 49: 305-313.
1964. On the migration of insects. Sonderdruck Aus.
Ergebnisee Biol. 17: 16-193.
:h, R. D., and M. W. Provost.
1965. The dispersal of Aedes taeniorhynchus. IV.
Controlled field production. Mosquito News 25:
2-8.
,st, M. W.
1952. The dispersal of Aedes taeniorhynchus. I.
Preliminary studies. Mosquito News 12: 174-190.
1953. Motives behind mosquito flights. Mosquito News
12: 106-109.
1957. The dispersal of Aedes taeniorhynchus. II. The
second experiment. Mosquito News 17: 233-247.
1960. The dispersal of Aedes taeniorhynchus. III. Study
method for migratory exodus. Mosquito News 20:
148-161.


80






C. DISPERSAL AND SEARCHING FLIGHTS: W. L. Bidlingmayer

The principal part of a mosquito's life consists of
various searching flights -- for nectar, blood, oviposition
sites, or resting places. These flights usually begin after
the female is > 14 hr of age and continue for the remainder of
its life. As with other species, Aedes taeniorhynchus
possesses a circadian rhythm of flight activity which,
imprinted by light-dark changes during the day of emergence,
results in an urge to fly at those same times on successive
days (Nayar and Sauerman 1971). All adults, whether male or
female, unfed, blood-fed or gravid, are apparently affected
(Provost 1953, 1974, McGaughey and Knight 1967). However,
once airborne, the purpose of the flight and associated
behavioral responses are determined by the mosquito's
immediate need and environmental conditions. The searching
flight is completed when a clue to the location of the
objective has been received and does not include the final
flight to the object.

During the day, Ae. taeniorhynchus rests on the ground in
wooded areas, often in leaf litter. At dusk it leaves the
woods and forays out into more open terrain, such as citrus
groves, residential areas, and pastures (Bidlingmayer 1971),
and returns at dawn. Since females of other species that
commute daily between woodland and open areas were found to
occur in larger numbers adjacent to woodlands than at greater
distances (Bidlingmayer and Hem 1981), Ae. taeniorhynchus is
probably similarly distributed. Aedes sollicitans rests in
open areas during the day where dense grasses and small shrubs
provide sufficient shelter (Bidlingmayer 1971, King et al.
1960). Since only those species that rest in grass during the
day were found to be evenly distributed across open terrain at
night, Ae. sollicitans may also be similarly distributed.

The distances traveled each night by mosquitoes are
poorly known. Although mark-release experiments with Ae.
taeniorhynchus were primarily concerned with migration, which
occurs only during the first night following adult emergence,
dispersal during the second and succeeding nights is due to
searching flights. Two releases of marked broods of Ae.
taeniorhynchus were made near Savannah, Georgia. The
percentage of each day's recoveries on days 1-4 after release
occurring at a distance of 6 or more miles from the release
point were 0%, 4%, 13%, and 27%, respectively, in the first
experiment and 2%, 6%, 4%, and 6% in the second experiment
(Bidlingmayer and Schoof 1957, Elmore and Schoof 1963). The
low percentages recovered showed these broods were slowly
moving outward by repeated searching flights and that a
migration had not occurred (c.f. Haeger, pp 77,79). In a
Florida experiment on Sanibel Island, by the 3rd day the non-
migrants in the broods had traveled 4 miles from the release


81






point to the end of the island where, in contrast to the
departed migrant mosquitoes, the presence of open water served
as a barrier to further flight (Provost 1957). Mosquitoes
containing bovine blood, some of them with blood meals < 24 hr
old, have been collected 1 mile from the nearest host (Edman
and Bidlingmayer 1969). It appears that searching flights of
about 2 miles each night are probable. Several studies have
shown total dispersals of about 20 miles (Bidlingmayer and
Schoof 1957, Elmore and Schoof 1963, Provost 1952, 1957) and,
wind assisted, of 30 to 60 miles (Harden and Chubb 1960), but
how much of these distances was accomplished during the
initial migratory phase and how much during the subsequent
searching flights is uncertain. After the initial migratory
flight, males are extremely sedentary (Provost 1952), even to
the extent of participating in the same swarm night after
night (Nielsen and Nielsen 1953). Females of Ae. sollicitans
disperse about 1 mile per day (Crans 1977).

Knowledge of differences in the flight behavior between
unfed, blood-fed, and gravid females is as important as the
differences between species. This information is best
obtained by employing non-attractant sampling methods
(Bidlingmayer 1974) such as the vehicle aspirator, which
collects resting mosquitoes in the daytime, and truck and
suction traps, which capture mosquitoes at night while making
searching flights. An analysis showed that both numbers and
the physiological composition of catches differed. Table 7.1
shows collections from two experimental areas and, to put non-
attractant collections in perspective, collections made by two
attractant samplers, the New Jersey light trap and a host-
baited trap (Bidlingmayer 1974).


Table 7.1. Percentages of blooded and gravid females of Aedes
taeniorhynchus found in vehicle aspirator collec-
tions and in catches from the truck, suction, New
Jersey light, and bait traps.*

Inland Area Beach Area
Trap Blooded Gravid Blooded Gravid

Vehicle 23 (39) 16 5 (18) 9 ( 8)
aspirator
Truck trap 12 (14) 24 1 ( 3) 18 (10)
Suction trap 9 ( 0) 5 1 (2) 8
New Jersey 2 3 < 1 2
light trap
Bait trap 1 1 < 1 (< 1) 1 ( 0)

*Percentages of Aedes sollicitans shown in parentheses.
Where values are not given, too few were captured for
analysis.


82






Since the vehicle aspirator collections were taken while
the population was at rest, this technique should provide the
most reliable estimate of the composition of the population.
The table shows that (1) neither the truck nor the suction
trap captured as high a percentage of blooded females as did
the vehicle aspirator, (2) the truck trap captured a higher
percentage, and the suction trap a lower percentage of gravid
females than the vehicle aspirator, and (3) the suction trap
percentages of blooded and gravid females were notably smaller
than those of the truck trap. Although larger numbers of both
species were captured near the beach, it is evident few blood
sources were available there.

The lower percentages of blooded and gravid females in
suction trap than in truck trap collections could be because
these females took a flight path which avoided the suction
trap, or alternatively, because the flight path of empty
(i.e., neither blooded nor gravid) females brought increased
numbers to the suction trap. Subsequent experiments showed
the latter hypothesis more probable; plywood suction traps
painted black captured larger numbers of mosquitoes than
unpainted traps, unpainted traps captured larger numbers than
clear plastic traps, and unpainted plywood traps placed in
visually exposed positions captured more mosquitoes than
similar traps in less conspicuous positions. It seems that
plywood suction traps were visually attractive to empty
females; and thus the searching flight is not random but
consists of a succession of flights to visually conspicuous
objects (Bidlingmayer and Hem 1980). Because the truck trap
is mobile, mosquitoes are captured before a response to the
vehicle occurred, therefore, all flying females in all
physiological stages are captured. Suction traps are fixed
and, depending upon the trap site, visible for a greater or
lesser distance. Apparently blood-seeking females are more
visually responsive to physical objects than other females and
consequently, suction trap catches were biased for this stage.

The searching flight has two phases: First is flight
toward the object from a long distance. The distance from
which the object will be perceived will depend upon its size
(an optical angle of 50 to 80 is indicated) and the number of
competing visual attractants near the object (Bidlingmayer and
Hem 1980). In the second phase, at an average distance of a
little more than 30 cm, the mosquito turns to avoid actual
contact with the object (Bidlingmayer and Hem 1979).

The flight activity of Ae. taeniorhynchus and Ae.
sollicitans is not uniform during the night. It is greater at
dusk than at dawn and greater at both times than during the
darkest hours of the night (Bidlingmayer 1967, 1974). Even
within the twilight periods there are large variations in


83






the numbers in flight as the twilight period is characterized
by rapid changes in light intensities. When four truck trap
collections were taken at approximately 20-minute intervals
for approximately 1.5 hr after sunset and again for a similar
period before sunrise, it was found that the catches of Ae.
taeniorhunchus taken closest to sunset (sunset + 20 min) or
sunrise (sunrise -20 min) were very small, whereas during the
following (sunset + 40 min) or preceding (sunrise -40 min)
collections, the largest catches of the evening and morning
twilight periods were taken (Fig. 7.6). Twilight catches
subsequent to (evening) or preceding (morning) the peak
catches were progressively smaller, although during the last
catches after sunset (or the first before sunrise) the numbers
captured were greater when the moon was present. The rapid
changes in numbers with rapidly changing illumination levels
during the twilight periods suggest that turnover is high
among the airborne population and that the duration of each
mosquito's flight is rather brief. The greatest number of
searching flights occurred at an illumination level of about
8.5 lux for Ae. taeniorhynchus and about 0.1 lux for Ae.
sollicitans (Fig. 7.6).

The intensity of flight activity during the night hours
(the hours between the two twilight periods) was closely
related to the amount of moonlight present, activity being
greater when the moon was full and when the quarter moons were
high in the sky (Fig. 7.6). During the night hours the flight
activity of Ae. taeniorhynchus was 10 times as great at full
moon as at new moon and for Ae. sollicitans nearly seven times
as great (Bidlingmayer 1974). For both species, the moonlit
half of quarter-moon nights showed about 2.7 times as much
flight activity as the moonless half. Suction traps also
showed increases in flight activity with moonlight, although
the increases were appreciably smaller.

An examination of the truck trap catches of Ae.
taeniorhynchus showed that during the twilight periods 18% of
all females taken contained blood (differences between
percentages with blood during evening and morning periods were
slight), whereas during the dark hours the rate was only 5%
(Bidlingmayer 1974). Comparable blood-fed rates for Ae.
sollicitans (again evening and morning percentages were
similar) were 23% and 5%,respectively. During the two
twilight periods over 30% of the Ae. taeniorhynchus captured
were gravid in contrast to only 7% during the night. Gravid
females have been observed to perform a slow, hovering flight
(McGaughey and Knight 1967, Nielsen and Nielsen 1953), which
may explain the seemingly excessive numbers taken in truck
trap collections (cf. Table 7.1). The proportions of gravid
females in twilight and night collections of Ae. sollicitans
were smaller, viz, about 13% and 5%, respectively. Twilight
suction trap catches also contained larger proportions of


84









100-


z
o
a.) Aedes toeniorhynchus
U
J 75-
-i
0
i--
Full Moon
50-









0 Evening I IMorning
A A A
SUNSET MIDNIGHT SUNRISE

100-
z
o
b.) Aedes sollicitans
75





CD ,Full Moon
4






FQ Moon LO Moon
U.
o 25 o


0_ New Moon
Evening I Morning
A A A
SUNSET MIDNIGHT SUNRISE







Fig. 7.6. Comparative levels of flight activity of female
mosquitoes captured by the truck trap at different moon phases
at different times. Catches taken during the first three
evening and first three morning collections were unaffected by
moonlight at any moon phase, and therefore these collections
have been combined.


85






gravid females than did night collections, although, since the
traps are visually attractive to empty females, the proportion
of gravid females was smaller than in truck trap catches.
Blood-fed females were infrequently taken in suction traps.
The greater proportions of blood-fed and gravid females in
twilight periods, superimposed on the larger numbers in flight
at these times, indicate that the searching flights of blooded
and gravid females were essentially confined to the twilight
periods (Bidlingmayer 1974, Edman and Bidlingmayer 1969).
Pregravids (females with partially digested bloodmeals and
developing ovaries) were also proportionately more abundant
during twilight periods. Apparently females with distended
abdomens, regardless of the cause, have similar flight
activity patterns.

The level of searching flights may be depressed by un-
favorable weather, principally temperature and wind. As
is implied by negative catches at temperatures of 100C or
lower, females do not initiate searching flights at low
temperatures. With rising temperatures, the flight activity
levels of Ae. taeniorhynchus and Ae. sollicitans increase
rapidly, reaching a maximum at 20C (Bidlingmayer 1974,
Blaustein and Crans 1980); higher night temperatures do not
produce greater flight activity.

Wind may affect the direction, elevation, and intensity
of mosquito flight. In wind tunnels mosquitoes fly upwind at
low air velocities, since the ground pattern must, within
certain rates, move beneath their eyes from front to rear
(Kennedy 1940). As air velocities increased, flight speeds
increased; the ground speed was unchanged. In the field,
however, mosquitoes may adjust to higher wind velocities
either by increasing their flight speed or, since wind
velocities are lower close to the ground, by reducing their
flight altitude. When wind velocities exceed their flight
speeds, about 3.2 to 4.8 km (2-3 miles) per hour (Klassen and
Hocking 1964, Provost 1960), the insect either must settle, or
it may fly downwind by increasing its elevation so that only
the larger ground patterns can be seen and thereby restore the
required apparent rate of movement (Klassen and Hocking
1964). The effect of high wind velocities upon the size of
trap catches has often been observed. Compared with winds of
< 1.0 miles per hour, truck and suction trap catches of Ae.
taeniorhynchus were reduced about 60% with each 1.6 km Tl
mile) per hour increase in wind velocity (Bidlingmayer 1967,
1974). It is emphasized that the trap catches and not
necessarily flight activity were reduced 60%, since the
mosquitoes could have been flying at higher elevations.


86






REFERENCES CITED


Bidlingmayer, W. L.
1967. A comparison of trapping methods for adult
mosquitoes: species response and environmental
influence. J. Med. Ent. 4: 200-220.
1971. Mosquito flight paths in relation to the
environment. 1. Illumination levels, orientation,
and resting areas. Ann. Ent. Soc. Am. 64:
1121-1131.
1974. The influence of environmental factors and
physiological stage on flight patterns of
mosquitoes taken in the vehicle aspirator and
truck, suction, bait and New Jersey light traps.
J. Med. Ent. 11: 119-146.
Bidlingmayer, W. L., and D. G. Hem
1979. Mosquito (Diptera: Culicidae) flight behaviour near
conspicuous objects. Bull. Ent. Res. 69: 691-700.
1980. The range of visual attraction and the effect of
competitive visual attractants upon mosquito
flight. Bull. Ent. Res. 70: 321-342.
1981. Mosquito flight paths in relation to the environ-
ment. Effect of the forest edge upon trap catches
in the field. Mosquito News 41: 55-59.
Bidlingmayer, W. L., and H. F. Schoof.
1957. The dispersal characteristics of salt-marsh
mosquito, Aedes taeniorhynchus (Weidemann) near
Savannah, Georgia. Mosquito News 17: 202-212.
Blaustein, L., and W. J. Crans.
1980. The influence of decreasing evening temperatures on
the activity of Aedes sollicitans. Proc. 67th Ann.
Mtg. N. J. Mosq. Control Assoc. pp. 99.
Crans, W. J.
1977. A summation of studies pertaining to the migrating
behavior of Aedes sollicitans and their potential
value to mosquito control. Proc. 64th Ann. Mtg.
N. J. Mosq. Control Assoc. pp. 56-58.
Edman, J. D., and W. L. Bidlingmayer
1969. Flight capacity of blood-engorged mosquitoes.
Mosquito News 29: 386-392.
Elmore, C. M., Jr., and H. F. Schoof.
1963. The dispersal of Aedes taeniorhynchus near
Savannah, Georgia. Mosquito News 23: 1-7.
Harden, F. W., and H. S. Chubb.
1960. Observation of Aedes taeniorhynchus dispersal in
extreme South Florida and the Everglades National
Park. Mosquito News 20: 249-255.
Kennedy, J. S.
1940. The visual responses of flying mosquitoes. Proc.
Zool. Soc. London (A) 109: 221-242.


87






King, W. V., G. H. Bradley, C. N. Smith, and W. C. McDuffie.
1960. A handbook of the mosquitoes of the southeastern
United States. Agric. Handbook No. 173, U.S. Dept.
of Agriculture. 188 pp.
Klassen, W., and B. Hocking.
1964. The influence of a deep river valley on the
dispersal of Aedes mosquitoes. Bull. Ent. Res.
55: 289-304.
McGaughey, W. H., and K. L. Knight.
1967. Preoviposition activity of the Black Salt-Marsh
mosquito, Aedes taeniorhynchus. J. Exp. Biol. 54:
745-756.
Nayar, J. K., and D. M. Sauerman, Jr.
1971. The effect of light regimes on the circadian rhythm
of flight activity in the mosquito Aedes
taeniorhynchus. J. Exp. Biol. 54: 745-756.
Nielsen, E. T., and A. T. Nielsen.
1953. Field observations on the habits of Aedes
taeniorhynchus. Ecology 34: 141-156.
Provost, M. W.
1952. The dispersal of Aedes taeniorhynchus. I.
Preliminary studies. Mosquito News 12: 174-190.
1953. Motives behind mosquito flights. Mosquito News
13: 106-109.
1957. The dispersal of Aedes taeniorhynchus. II. The
second experiment. Mosquito News 17: 233-247.
1960. The dispersal of Aedes taeniorhynchus. III. Study
methods for migratory exodus. Mosquito News 20:
148-161.
1974. The dispersal and migration of mosquitoes.
Proceedings of a Mosquito Abatement Seminar and
Work Conference, University of Manitoba. pp. 4-39.


88






CHAPTER 8


LABORATORY FLIGHT BEHAVIOR AND ENERGETIC

J. K. Nayar and D. M. Sauerman, Jr.

Flight behavior:

In the laboratory, Aedes taeniorhynchus and Aedes
sollicitans adults exhibit a nocturnal flight activity pattern
that Nayar and Sauerman (1969, 1971a, 1974) have studied in
detail. Week-old adults of Ae. taeniorhynchus were maintained
on a 10% sucrose solution under a light-dark cycle of
alternating 12 hr (LD 12:12) at 27C in an acoustic bioroom.
Flight sound continuously recorded for more than a week showed
that flight occurred at both light-off and light-on, forming a
biomodal pattern. At light-off, flight activity lasted about
1 hr, with maximum activity lasting for about 35 min. At
light-on, flight activity lasted about 30 min, with maximum
activity lasting for about 20 min (Fig. 8.1). The period
between two light-off peaks was 24 hours.

Effects of different light cycles on flight activity patterns:

Newly emerged females reared as larvae under LD 12:12,
when maintained under either continuous light (LL) or darkness
(DD), did not exhibit any flight activity rhythmicity during
the next 10 days. There were sporadic individual flights,
none of them lasting over 2 min (Nayar and Sauerman 1971a).
A light or dark stimulus of 12 hr during the first 24 hr
after emergence did not initiate a sustained diurnal flight
activity. However, in females maintained under LD 12:12 after
emergence, a first peak of flight activity occurred 24-36 hr
after emergence. Independent flight activity rhythms became
established about 36 hr after emergence. There was very little
activity in the light or the dark periods, except at the
transition of light during the first week of adult life, but
thereafter marked increase in flight activity during both the
light and dark periods occurred. This increase in flight
activity during the second week and thereafter is apparently
related to physiological aging of the mosquitoes.

Females entrained under a LD 12:12 regime for 5 days
after emergence showed, when subjected to continuous DD, a
persistent biomodal flight activity pattern (Fig.8.1). This
indicated that the flight activity pattern was endogenously
determined. The period between the main peaks became 23.5 hr
under continuous DD. However, when entrained females were
subjected to continuous LL, they appeared to become
hyperactive and lost the two-peaked flight activity rhythm,


89






and instead displayed short irregular periods of increased
activity after the first 12-hr period of light (Fig. 8.1).


(a)
LDI212








9'(b)
5 LD1212- DD






(c) LDI212+LL






I- 7Ah--- Days



Fig. 8.1. Mean flight activity in (a) LD 12:12, (b)
continuous DD following LD 12:12, and (c) continuous LL
following LD 12:12. (From Nayar and Sauerman 1971a.)

Other effects of light stimuli and light cycles have been
studied in detail by Nayar and Sauerman (1971a). The main
features can be summarized as follows. Flight activity
rhythms can be entrained to a new light regime within 24 to 36
hr, which is rather fast as compared to other insects. An
early light-off does not reset the phase of the rhythm, but a
delayed light-off does. The flight activity rhythm can be
entrained to 24 hr light regimes other than LD 12:12, but a
single stimulus of less than 12 hr is not effective in
initiating a bimodal circadian rhythm. Frequency demultipli-
cation within certain limits can entrain the flight activity
rhythm to 24 hours.

In the laboratory, unfed Ae. taeniorhynchus females, when
fed a blood meal to repletion and flown in the acoustic
recording chambers, exhibited a bimodal pattern of flight
activity only when fed 8 hr before the change from light to


90






dark (Nayar and Sauerman 1971b). This would indicate that in
the field those females that feed on cattle in open pastures
soon after sunset would be able to fly easily to resting
places before sunrise.

These studies have demonstrated that the basic bimodal
pattern of flight activity is a persistent property of the
circadian oscillating system. This further suggests that the
flight activity rhythm provides a framework for other
activities that involve flight -- such as mating, host-
seeking, sugar-feeding and oviposition -- which are discussed
in this bulletin.

Flight energetic:

Mosquitoes do not fly or feed well until several hours
after emergence. Unfed mosquitoes, 1 or 2 days old, were
capable of 1 to 2 hr of vigorous flight on a flight mill,
after which they slowed down and were able to fly for another
1 to 2 hr. Nayar and Van Handel (1971) flew newly emerged
unfed Ae. taeniorhynchus and Ae. sollicitans adults of both
sexes on a flight mill and found that only glycogen reserves
were utilized for flight; triglyceride reserves and other
lipids were not used. Blood-fed and glucose-fed adults were
also flown either to exhaustion or for one hour. In
experiments in which respired 002 was collected, the
mosquitoes were fed radioactive sucrose solution and flown on
a flight mill in closed air-tight 750 ml boxes.

In spite of the ability of female mosquitoes to
synthesize triglycerides rapidly both from sugar and from
blood, these lipids are not mobilized rapidly enough to make
a significant contribution to the increased energy demand
during flight. In unfed mosquitoes, utilization of
triglycerides continues during flight, but not at a faster
rate than in non-flown controls. The non-availability of
triglycerides as a flight substrate for mosquitoes strengthens
the impression that Diptera do not use fat for flight.
Utilization of carbohydrates in flight was 0.08 to 0.10 cal
(0.33 to 0.42 J)/1000 m or 27 to 37 cal (113 to 155 J)/hr
per g, whether calculated from the utilization of glycogen (in
unfed and blood-fed mosquitqos) or from the production of
carbon dioxide (in glucose-U- C fed mosquitoes). The maximum
metabolic rate during sustained flight was four to five times
as great as in non-flown controls. In sugar-fed mosquitoes,
glycogen and triglycerides accumulated during flight.
Glycogen was not utilized as a flight substrate as long as
sugar was available. Starved mosquitoes and mosquitoes flown
to exhaustion could resume vigorous flight immediately after a
sugar meal. Trehalose levels did not decline during vigorous
exhaustive flight. In unfed mosquitoes, the flight following


91






a rest period after exhaustion was sustained by residual
glycogen; glycogen levels did not increase in females.

Carbohydrates other than sucrose can also support
flight. In experiments with Ae. taeniorhynchus females fed
different carbohydrates and flown on a flight mill, glucose
supported the maximum speed of flight immediately after
feeding (Nayar and Sauerman 1971c). This was followed by
sucrose, fructose, mannose, dextrin, maltose, raffinose,
melizitose, and trehalose. None of the pentoses supported
flight. Neither did sorbose, lactose, cellobiose, glycogen,
inulin, a-methyl mannoside, dulcitol, or inositol. Galactose,
melibiose, a-methyl glucoside, glycerol, mannitol, and
sorbitol did not support flight immediately after feeding.
However, after 24 hr of feeding, these carbohydrates supported
flight as soon as the mosquitoes were mounted on the tethered
flight mill.

In other studies, Nayar and Sauerman (1972) flew sugar-
fed female Ae. taeniorhynchus and Ae. sollicitans for 4.5 hr
on a flight mill twice a week for the eight weeks of their
life span. They found that flight performance is little
affected by aging; i.e., flight activity remained at peak
performance level for the first 5 weeks and declined
thereafter. Females flew vigorously for the first 1 to 2 hr
and then gradually slowed down towards the end of each flight
period. Glycogen was the only energy reserve utilized during
sustained tethered flight. It was nearly exhausted in females
flown for the eight weeks. Different amounts of glycogen were
utilized during efficient sustained flight, e.g., 30 to 40 cal
(125.6 to 167.4 J)/hr per g during the second through fifth
weeks when flight was maximum as compared with 14 to 24 cal
(58.6 to 100.5 J)/hr per g during the sixth to eighth weeks
when flight was considerably slower. Females maintained on
sugar ad lib. achieved maximum reserves of glycogen (0.8 cal
(3.4 J7female) and triglycerides (5.5 cal (23 J)/female)
during the second week, and they maintained these levels until
the sixth week.

The non-availability of fat for flight energy has
implications with respect to migration. Aedes taeniorhynchus
adults reared under crowded conditions show a very high level
of flight activity soon after emergence, on the first change
from light to dark (Nayar and Sauerman 1969). Enough glycogen
remained from the pupal stage for a few hours of flight.
Flights beyond the initial flight will depend on the avail-
ability of sugar meals. Feeding on nectar provides immediate
energy, but prolonged rest after the meal would lead to the
accumulation of glycogen and fat, and the latter cannot be
used for flight. If the exhausted mosquito acquired a blood
meal instead of nectar, at least a day would be required
before enough glycogen could be synthesized from blood protein


92






to permit resumption of long flights (Nayar and Van Handel
1971). Furthermore, most of the nutritive value of the blood
would be used for egg development, which also limits flight
potential. A blood meal without nectar intake severely limits
the ability of these salt marsh mosquitoes to disperse over
long distances.

Mosquitoes tethered to a flight arm normally fly to
exhaustion. Whether these same distances are flown in free
flight is not known. In a flight mill, only propulsion energy
is used, not lift energy. The important questions regarding
the percentages of time an individual mosquito spends on the
wing, during searching, dispersal, and swarming flights,
remain unresolved. Field evidence, discussed in the section
"swarming, migration, and dispersal" suggests a time span of
minutes rather than hours for searching. However, the main
finding that both sexes of mosquitoes fly using carbohydrate
reserves and not fat, will remain valid.


93






REFERENCES CITED


Nayar, J. K., and D. M. Sauerman, Jr.
1969. Flight behavior and phase polymorphism in the
mosquito Aedes taeniorhynchus. Entomologia exp.
appl. 12: 365-375.
1971a. The effects of light regimes on the circadian
rhythm of flight activity in the mosquito Aedes
taeniorhynchus. J. Exp. Biol. 54: 745-756.
1971b. The effects of diet on life-span, fecundity and
flight potential of Aedes taeniorhynchus adults.
J. Med. Ent. 506-513.
1971c. Physiological effects of carbohydrates on survival,
metabolism and flight potential of female Aedes
taeniorhynchus. J. Insect Physiol. 17: 2221-2233.
1972. Flight performance and fuel utilization as a
function of age in female Aedes taeniorhynchus.
Israel J. Ent. 7: 27-35.
1974. Circadian rhythm in Florida mosquitoes. pp 607-
611. In Chronobiology, L. E. Scheving, F. Halbert,
and J. E. Pauly, eds. Igaku Shoin Ltd., Tokyo.
(Symposium International Study of Biological
Rhythms held in Little Rock, Arkansas.)
Nayar, J. K., and E. Van Handel.
1971. The fuel for sustained mosquito flight. J. Insect
Physiol. 17: 471-481.


94






CHAPTER 9


BLOOD-FEEDING BEHAVIOR

J. D. Edman

It is the intense annoyance caused by the blood-feeding
behavior of salt marsh Aedes that make these pests so
important. Both early and modern descriptions of the Florida
coast include numerous, often humorous, references to the
unbelievable biting densities of salt marsh mosquitoes that
were encountered. Those who have personally experienced it
can not help but wonder how the Aboriginal Indians and native
wildlife were able to coexist with these blood-thirsty hordes.
Even today, in parts of south Florida where no attempt is made
to control salt marsh mosquitoes, their influence on the
distribution and behavior of vertebrate populations (including
humans) remains considerable.

Frequency of Blood-Feeding

As indicated in chapters 6 and 10, Ae. sollicitans and
Ae. taeniorhynchus differ significantly in their ability to
produce eggs without blood. Even though autogenous, Ae.
taeniorhynchus can blood-feed the first and second days
following emergence and thereby enhance their fecundity; the
natural occurrence of such supplementary blood feeding is
unknown. It may be that autogenous females seldom embark on
host-seeking flights until after their initial oviposition.

Except for the first gonotrophic cycle in autogenous Ae.
taeniorhynchus, the blood feeding patterns of salt marsh
mosquitoes are similar to those of many other Florida
species. Females generally begin host-seeking 2-4 days after
emergence when their ovaries are in resting stage II (cf.
Chapter 10) and, if successful, require 4-6 days for egg
development and oviposition prior to seeking each additional
blood meal.

Diel Blood-Feeding Patterns

Aedes sollicitans and Ae. taeniorhynchus both have
temporal activity patterns best described as diurnal-
crepuscular (Edman and Bidlingmayer 1969). All evidence
indicates that females embark on host-seeking flights during
evening and (to a lesser extent) morning twilight periods.
Nonetheless, resting females will opportunistically attack
hosts that invade their immediate vicinity during the
daytime. Neither species blood-feeds to a significant degree
during the dark part of the night, but bright moonlight may
extend crepuscular blood-feeding activity periods
(Bidlingmayer 1964). Host-seeking Ae. taeniorhynchus are most


95




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