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Title: life history and ecology of Baetisca rogersi Berner (Ephemeroptera, Baetiscidae)
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Title: life history and ecology of Baetisca rogersi Berner (Ephemeroptera, Baetiscidae)
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Creator: Pescador, Manuel L.
Publisher: Florida State Museum, University of Florida,
Copyright Date: 1974
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of the c,
FLORIDA STATE MUSEUM
Biological Sciences
Volume 17 1974 Number 3





THE LIFE HISTORY AND ECOLOGY
OF BAETISCA ROGERSI BERNER
(EPHEMEROPTERA: BAETISCIDAE)


Manuel L. Pescador
ST William L. Peters
I


UNIVERSITY OF FLORIDA


GAINESVILLE







Numbers of the BULLETIN OF THE FLORIDA STATE MUSEUM, BIOLOGICAL
SCIENCES, are published at irregular intervals. Volumes contain about 300 pages
and are not necessarily completed in any one calendar year.








OLIVER L. AUSTIN, JR., Editor


Consultants for this issue:

. LEWIS BERNER
/' -f F. CLIFFORD JOHNSON









Communications concerning purchase or exchange of the publication and all manu-
scripts should be addressed to the Managing Editor of the Bulletin, Florida State
Museum, Museum Road, University of Florida, Gainesville, Florida 32601.


Publication date: 30 January 1974


This public document was promulgated at an annual cost of $2,353.14
or $2.353 per copy. It makes available to libraries, scholars, and all
interested persons the results of our researches in the natural sciences,
emphasizing the Circum-Caribbean Region.


Price: $2.40







































FIGURE 1.-LATERAL VIEW OF MALE IMAGO OF Baetisca Rogersi.






































FIGURE 2.-LATERAL VIEW OF MALE SUBIMAGO OF B. Rogersi.


























-, 4


I.

I'*
It '
.


v_ N


b--
*r,


FIGURE 3.-Dorsal view of mature female nymph of B. rogersi [after Berner (1950)].


*/ /


































THE LIFE HISTORY AND ECOLOGY OF BAETISCA ROGERSI
BERNER (EPHEMEROPTERA: BAETISCIDAE)1

MANUEL L. PESCADOR AND WILLIAM L. PETERS2

SYNOPSIS: This report describes the life history and ecology of Baetisca rogersi Ber-
ner (Ephemeroptera: Baetiscidae) in northwestern Florida. It includes a description
of external morphology, duration, and behavior of the different life history stages and
also considers seasonal distribution, growth, and emergence. It discusses factors in-
fluencing ecology of the species, particularly those affecting growth, development, and
seasonal distribution, and identifies associated arthropods.

1 The research was supported by a grant from the Cooperative State Research
Service, USDA, P.L. 86-106, to Florida A & M University, William L. Peters, Princi-
pal Investigator.
2 Manuel L. Pescador, a graduate student in the Department of Biological Science,
Florida State University, Tallahassee, under a cooperative agreement between Florida
State University and Florida A & M University, submitted a portion of this paper in
partial fulfillment of the requirements for the Master of Science degree, Department
of Biological Science, Florida State University.
William L. Peters is an Associate Professor of Entomology, School of Agriculture
and Home Economics, Florida A & M University, Tallahassee, Florida. Manuscript
accepted 10/15/72.

Pescador, Manuel L. and William L. Peters. 1974. The Life History and Ecology
of Baetisca rogersi Berner (Ephemeroptera: Baetiscidae). Bull. Florida State Mus.,
Biol. Sci., Vol. 17, No. 3, pp. 151-209.




& 70. eL,


v, /7
152 BULLETIN FLORIDA STATE MUSEUM Vol. 17, No. 3
iiu. .3
TABLE OF CONTENTS

INTRODUCTION -____......-........ . .. -_...... ----.-------------.152
ACKNOWLEDGMENTS _---- ----153
METHODS ......................--------------------- -------- ------ ------153
DESCRIPTION OF STUDY AREA _........................__---- -------- --- __.157
RELATIONSHIP AND GEOGRAPHICAL DISTRIBUTION OF Baetisca rogersi ..__._..... 162
LIFE HISTORY AND ECOLOGY -___.-------.--___ ----__ --.__ -------_.. 164
THE EGGS -....-- .......-_............_....--------------------------- 164
External Morphology ....-------....--.........---- ..------------------- ----- 164
Incubation Period ----..--.._..__.. ------------------------ 165
THE NYMPHS ...------.. ..... ..... .. .............---. .-- .----------167
External Morphology -__--.___.___---------- .....-----167
Growth and Development ---__- .-------.---- --...---..179
Habitat and Habits . __ .. _.-----.-......----- .. 186
Associated Organisms ------------------------.-- .. 192

THE SUBIMACOS ..........- ....... ... ....194
External Morphology .-----....... --.. --... ----.. ---....----...--.......-194
Emergence __- --...-_. _____................----------------------.. 197
Flight Activities ..--_ _-...-----_.______ -- ........ 200
Duration --.. ----- -____ __ __ _-_-__----- -.200
Molting --................ --..---- ...............- ..... .......... ...... 201
Predation ._---__-..... ..._ -------------------- ----........201
THE IMAGOS ................... ........-------------------------...... 201
External Morphology ..._._....------------------ --- .. --_ .....201
Flight Activities ----------............ ---......-----... 204
Life Span ...... -----.-_......-----------... .... .... 204
Parthenogenesis .-___ .. _... .... --.. _...... --- -- --.204
Egg Number ------------ ---------------------- ---------205
Seasonal Distribution ...._-_------------------ --------..- 206
SUMMARY .........---- -----. _. _.__-._.-------- ----- ----206
LITERATURE CITED .-...------.....__...._ ____ -.... -...207


INTRODUCTION

The life history and ecology of most mayfly (Ephemeroptera) species
in North America are unknown. Recently ecological studies of aquatic
insects have attracted the attention of many biologists, especially in
North America, Europe, and Africa because of these insects' importance
in freshwater communities, their role in fisheries, and their sensitivity
to pollution. Mayflies are an excellent tool for studying environmental
relationships and the importance of a favorable environment for all forms
of aquatic life. Knowledge of their ecology and life history is essential
in understanding the biological structure of freshwater streams and lakes.








PESCADOR AND PETERS: BAETISCA ROGERSI


To help enlarge our knowledge of mayfly species in the southeastern
United States, investigations of their ecology have been initiated at
Florida A & M University. This study, which is a part of the main re-
search project at Florida A & M University, investigates ecology, life
history, seasonal distribution, and habitat of Baetisca rogersi Berner, and
lays a foundation for continued work.
B. rogersi is common in northern Florida, southern Alabama, Georgia,
and South Carolina. Nymphs live in shallow rocky or sandy streams
with a moderately slow to fast current. Berner (1950) summarized his
observations on ecology, seasonal distribution, habits, and life history
of the species. He briefly described the general habitat and discussed
the species' distribution.
The objectives of this study were to determine: (1) stages in the
life history, (2) ecology of the life stages, (3) habits of both nymphs
and images under field and laboratory conditions, and (4) seasonal
distribution of B. rogersi.

ACKNOWLEDGMENTS
We extend our sincere appreciation and thanks to the many persons who have
given valuable aid, assistance, and encouragement during the course of this investi-
gation.
We especially thank E. C. Beck, Bureau of Entomology, Florida Division of
Health, Jacksonville; W. M. Beck, Jr., Florida A & M University; E. L. Bousfield,
National Museum of Canada, Ottawa; G. W. Byers, University of Kansas, Lawrence;
O. S. Flint, Jr., U. S. National Museum; J. J. Franklin, Florida A & M University;
H. H. Hobbs, U. S. National Museum; S. G. Jewett, Jr., Portland, Oregon; R.
Ocampo-Paus, Florida State University; P. J. Spangler, U. S. National Museum; V.
Sullivan, Iowa State University, Ames; and M. J. Westfall, Jr., University of Florida,
Gainesville, for identification of specimens.
We thank Lewis Berner, University of Florida, for his encouragement during the
study and for permitting use of the full nymph illustration.
We thank E. T. Hall, State Water Quality Control Board, Atlanta, for specimens
of B. rogersi used in compiling distribution records, and Janice G. Peters, Florida
A & M University, for preparation of the illustrations under our supervision. We
gratefully acknowledge Jerome Jones, Philip T. P. Tsui, and Paul H. Carlson for their
valuable help and encouragement during the course of the study. We wish to thank
Charles E. Rockwood, Florida State University, for permission to conduct a portion
of this study on his property at Bear Creek, Gadsden County, Florida. We offer
our deep appreciation to Michael Hubbard, Florida State University for help in con-
ducting the behavior study. We also thank D. R. Davis, North Florida Experiment
Station, Quincy, for permitting use of the 1968-1969 data on air temperature. To
the many others who contributed to this study we offer our sincere appreciation.

METHODS

We used many methods to collect and rear specimens, but give only
successful methods here as an aid to future studies. All eggs used. in
this study came directly from female subimagos and images. Female







BULLETIN FLORIDA STATE MUSEUM


gonads dissected with jeweler's forceps were placed in small plastic
petri dishes, 60 X 15 mm, half filled with distilled water. Eggs ex-
tracted from each female imago were counted under a dissecting
microscope with an ocular grid to determine reproductive potential. To
determine whether B. rogersi exhibits parthenogenesis, we took eggs from
female subimagos and images reared individually in separate aquaria,
and incubated the eggs in distilled water to avoid possible sperm con-
tamination.
Eggs were fertilized by artificial insemination, achieved by crushing
the reproductive organs of a male imago and a female imago in a
depression slide filled with distilled water or Hobson's Ringer Solution
as Barnes (1937) suggested. After 3 hours in the insemination medium
the eggs were transferred into small, plastic petri dishes containing either
steam or distilled water. They were then incubaetd at room tempera-
tures of 200 C to 32.20 C. Water was changed every 2 days and water
temperatures recorded daily. Nymphs hatched from eggs were reared
through the first three instars in the laboratory, but all died before
achieving the fourth instar. Field collections were necessary to supple-
ment the life history.
We made field collections of the first five instar nymphs using
Anderson's (1959) modified flotation technique. We also collected
young nymphs from fresh samples of bottom substrate brought in from
the study area at weekly intervals for 3 months, September to November
1968. Although laborious, this technique allowed us to collect live
small nymphs free from injuries or mutilation. Most fourth to sixth in-
star nymphs were obtained this way. The seventh to twelfth instars were
collected with a plastic handscreen throughout the study, December
1967 to July 1969.
We carried live nymphs to the laboratory in plastic buckets con-
taining a small quantity of stream water with a dampened cloth in the
bottom of the container. If no attachment surface is provided, the
nymphs will cling to one another and injure themselves as they splash
against the sides. Rocks or gravel are unsuitable for attachment be-
cause they tumble about and can damage the specimens. Wet moss
can be substituted for cloth.
Early instar nymphs were reared in small plastic petri dishes of
stream water with a thin layer of fine sand in the bottom for an attach-
ment surface. Food (fresh, bottom substrate and living diatoms) and
water were changed every 2 days. The water was aerated by the vibra-
tion of air pumps placed near the pans containing the petri dishes.
These compressors were primarily used to aerate large aquaria, but their
vibration alone agitated the water in the dishes enough to aerate it.


Vol. 17, No. 3







PESCADOR AND PETERS: BAETISCA ROGERSI


The seventh to last instar nymphs were reared in 2 gallon glass
aquaria. Each aquarium contained 5 liters of stream water which was
changed weekly. The water was treated with streptomycin sulfate
USP (0.5 cc/3.5 1 water) and was aerated and filtered by a single air-
pump-operated filter. Each aquarium received additional aeration from
two air stones connected to an air compressor. Three plastic screen
rearing cages per aquarium confined and separated individual nymphs.
Specimens intended for parthenogenetic tests were reared individually in
different aquaria to avoid possible sperm contamination. All eggs and
spermatozoa came from specimens reared this way. Plastic screen
covers protected the rearing cages from dust and prevented the escape
of emerging adults. A thin layer of sand and gravel was placed in the
bottom of each cage and food was added every 2 days. Bottom substrate
from the study areas composed of sand, gravel, detritus, water moss
(Leptodictyum riparium), and filamentous algae (Spirogyra sp.) served
as a food source.
Although we made weekly attempts to collect B. rogersi adults with
field light traps from March to May 1968, we caught only two female
subimagos. Both came to light on 28 April 1968 at 9:45 PM. Equip-
ment used on different occasions included a gasoline 2-mantel pressure
lantern, a 200-250 volt mercury vapor bulb powered by a 1-hp generator,
and a battery operated 110 volt black light.
The following emergence season we used another method to col-
lect adults in the field. The nymphs of B. rogersi climb onto fixed
solid objects above water level to emerge. We captured newly emerged
subimagos with insect nets as they rested before taking flight.
Nymphs intended for gut analyses were preserved in 10% formalin.
The whole gut of five specimens of different sizes was dissected monthly
and the contents extruded onto a slide with Turtox CMC-10-Non-
Resinous Mountant. To determine the percentage composition of de-
tritus, algae, and indigestible material, the slides were studied and counts
were made on three nymphs per month using a method similar to that
of Minshall (1967): the entire slide was scanned and five representative
fields were counted, each representing one square of an ocular grid.
Individual clumps of detritus, individual diatom frustules, individual
mineral particles, recognizable filamentous algae, and arthropod re-
mains were counted as separate items.
Nymphal habitat preferences were studied in the field and in
two sets of laboratory experiments. Three trials were run in each ex-
periment, using 36 X 12 X 2-inch galvenized iron tray filled with stream
water and divided into three equal sections: A, B, and C (Fig. 4 A).
The bottom of section A was covered with a mixture of sand, gravel, and


1974







BULLETIN FLORIDA STATE MUSEUM


FIGURE 4.-A) Experimental laboratory equipment used to study habitat preference
of nymphs. B) Collecting site at Bear Creek.

pebbles; section B with sand only; and section C with leaf litter. Each
section was aerated by an air stone. Fifteen ninth to eleventh instar
nymphs were introduced into the tray and data recorded after 12, 36,
and 48 hours. In the first experiment, a high-intensity lamp lighted the
entire tray. In the second experiment one section was exposed to a
light source and the remaining sections covered. In trials I and II,
section C was lighted for the first 12 hours while the remaining two
sections were covered. Then section B was lighted while A and C
were dark. Section A was lighted for the last 12 hours. In trial III,
section A was lighted first, followed by B and C.
To study the dorsal light response, we placed 10 nymphs in a glass
tube filled with stream water. In an otherwise dark room, a beam of
light was projected into the tube and nymphal behavior was recorded.
To determine hourly adult emergence in nature, we regularly counted
emerging subimagos on 23 tree stumps in Rocky Comfort Creek. After
first removing exuviae from previous emergences, fresh exuviae were
collected at one-hour intervals from 8:30 AM to 2:30 PM. The time
required for subimaginal emergence was determined from the moment
the nymphal thoracic notal shield began to split until the subimago
emerged from the nymphal exuvia. Habits shown by the subimagos were
noted.
Laboratory subimago data included hourly emergence, time required
for subimaginal emergence, duration of the subimaginal stage, and time
required for the subimaginal molt. Data on longevity or life span of


Vol. 17, No. 3







PESCADOR AND PETERS: BAETISCA ROGERSI


images included the time of molt and the time of death. Physical
factors pertinent to subimaginal duration and imaginal longevity were
recorded.
We conducted tests for dissolved oxygen, free carbon dioxide, and
calcium carbonate to determine possible factors important in nymphal
life cycle and distribution. We measured water temperatures 3 inches
below the water surface with a pocket thermometer and determined
water velocity by the cork flotation method. Water chemistry, pH, and
water velocity were recorded at monthly intervals and water tempera-
ture at weekly intervals.

DESCRIPTION OF THE STUDY AREAS
Field studies were conducted at Rocky Comfort Creek and Bear
Creek in Gadsden County, Florida. Both streams are tributaries of
the Ochlockonee River. The sites for all collections and field studies
were: (1) TIN, R3W, S32, a small riffle portion of Rocky Comfort
Creek, at bridge on a dirt road 6 miles south of State Highway 268; and
(2) TIS, R3W, S30, a short sandy stretch of Bear Creek, at bridge on
a dirt road 8 miles south of State Highway 268 and 1 mile north of
State Highway 65C (Fig. 6 B).

ROCKY COMFORT CREEK
Rocky Comfort Creek is a small spring-fed stream. It flows approxi-
mately 13.2 miles and averages about 33 feet wide. The substratum is
mainly of a mixture of sand and clay except in the upper reaches where
eroding limestones and riffles prevail. Much of the substratum supports
no vegetation.
Along the banks of the creek are thick stands of trees and shrubs
whose leaves are the stream's principal source of organic detritus.
Among the higher plants are: Sambucus canadensis (common elder),
Itea virginica (sweet spire), Salix nigra (black willow), Carpinus
caroliniana (American hornbeam), Fagus grandifolia (American beech),
Pinus glabra (spruce pine), P. clausa (sand pine), and Quercus nigra
(water oak).
One permanent sampling station was in a riffle area 3.9 miles from
the mouth of the stream (Fig. 5); it averaged 15 feet wide by 30 feet
long. The basic substratum was rubble and gravel integrated with
coarse sand in quieter water. Current velocity ranged from 0.9-1.3
feet per second. Maximuim depth was 2 feet, which dropped as low as
0.5 foot in summer. One-half of the sampling area received direct sun-
light. Figure 7 gives seasonal variations in air and water temperatures.


1974







BULLETIN FLORIDA STATE MUSEUM


FIGURE 5.-A, B) Views of collecting station at Rocky Comfort Creek.


Water temperatures ranged from 50 C in January to 250 C in mid-
summer. The stream was mildly acid to circumneutral (6.7-7.1 pH).
Dissolved oxygen content ranged from 4.7 mg/1 to 7.6 mg/1 in winter,


Vol. 17, No. 3







1974 PESCADOR AND PETERS: BAETISCA ROGERSI

A




Locality
records


Gadsden
County,
Florida


. Study sites


FIGURE 6.-A) Geographical distribution of B. rogersi. B) Map of Rocky Comfort
and Bear Creeks showing study areas.







BULLETIN FLORIDA STATE MUSEUM


30-

25-

20-

15-

-010-

5-
e 0
a )
u

425-
LI
020-
-a
15-

10-

5-


Air


----ROCKY COMFORT CREEK
....... BEAR CREEK


Water


SEP. OCT, NOV. DEC. JAN. FEB. MAR. APR. MAY JUNE JULY AUG.
1968 196 9

FIGURE 7.-Monthly air and water temperatures at the study areas, September 1968
to August 1969. The dotted lines show monthly temperature ranges.

and free carbon dioxide content was fairly constant throughout the
year (Fig. 8).
The substratum of the sampling area supported no vegetation ex-
cept for thick growths of the water moss, Leptodictyum riparium, and a
filamentous algae, Spirogyra sp. in a narrow strip at the upper reaches.
Along the marsh zone of the station were plant communities composed of
Panicum regidulum, Scirpus cyperinus, Solidago altissimum., and Pluchea
camphorata.

BEAR CREEK
Bear Creek is basically the same as Rocky Comfort Creek, but its
substratum is mainly coarse shifting sand and it has no cascades. The
streams are confluent near the main outlet. Bear Creek flows approxi-


Vol. 17, No. 3







PESCADOR AND PETERS: BAETISCA ROGERSI


170 -

16.0-

15.0-

14.0-

13,0-

12,0-

11.0 -

10.0 -

8,0-

E 70 -

6,0-

50 -

4.0-

3.0-

2,0-

1,0-


I--
CaCO3 //

\ \




........














'4,




. . .I


SEP. OCT. NOV. DEC. JAN. FEB. MAR. APR. MAY JUNE JULY AUG.
1968 1969
FwUsRE 8.-Monthly calcium carbonate, dissolved oxygen, and free carbon dioxide
content of Rocky Comfort and Bear Creeks, September 1968 to August 1969.
mately 10.2 miles and averages 21 feet wide. Typical of most sand-
bottomed streams, the substratum supports no vegetation. Woody
plants growing along the banks are the principle source of organic
detritus.


'
/ \














.. "-- :-
---- ROCKY COMFORT CREEK
......... BEAR CREEK


1974







BULLETIN FLORIDA STATE MUSEUM


A permanent station, mainly for ecological observations, was 1.9 miles
from the mouth of the stream and measured approximately 20 feet by
15 feet (Fig. 4 B). The current velocity ranged from 0.8-1.2 feet per
second. Water temperatures were similar to Rocky Comfort Creek
(Fig. 7); Figure 8 shows chemical and physical characteristics. Except
for scattered growths of Leptodictyum riparium and Spirogyra sp. at the
submerged concrete wall of the bridge, the sampling area substratum
was relatively bare. Plants growing in the marsh zone were similar
to those found at Rocky Comfort Creek.

RELATIONSHIPS AND GEOGRAPHICAL DISTRIBUTION
OF BAETISCA ROGERSI

The genus Baetisca, established by Walsh (1862) for the species
Baetisca obesa (Say), was known only form images until Walsh (1864)
reared the nymphs. Baetisca represents a monobasic family Baetiscidae
which was first recognized by Eaton (1883) as "Section 11 of Baetisca."
Authorship of the name was established by Lameere (1917) as tribe
Baetiscini. Subsequently the family has been universally recognized at
hierarchic levels of subfamily to family.
Baetisca is a highly specialized genus as indicated in the phylogeny
presented by Edmunds (1962). The nymphs of the genus are distin-
guished by the presence of a massive mesothoracic shield which functions
as a gill chamber (Fig. 3) and a greatly enlarged labial submentum
(Fig. 15 E). The anal area of the fore wings of the images is greatly
enlarged with only two anal veins present (Fig. 24 A). Vein CuA of
the fore wings is unbranched and both veins CuA and CuP terminate
before the anal angle (Fig. 24 A). The penes of the male imago are
cone-shaped and apically divided (Fig. 24 E, F). The genital forceps
of the male images are two-segmented, with the first segment indented
giving the appearance of segmentation (Fig 24 E). Since Traver
(1931), however, all major accounts of Baetisca indicate the forceps
of the male images to be three-segmented except two drawings of
Traver (1935) which show only two segments. This led to the study of
the genital forceps of the males of all species of Baetisca available to
us, and we found that the genital forceps consist of two segments
(Pescador and Peters 1971).
Species of Baetisca occur only in North America with the center of
diversification in eastern North America, especially the southeast. The
following list gives known species, recognized synonymies, and general
distribution of the species:


Vol. 17, No. 8







PESCADOR AND PETERS: BAETISCA ROGERSI


B. baikovi Neave, 1934. Manitoba, Quebec, Illinois, Missouri, West Virginia,
Tennessee.
B. becki Schneider and Berner, 1963. Florida.
B. callosa Traver, 1931. Quebec, New York, West Virginia.
B. carolina Traver, 1931 (=B. thomsenae Traver, 1937). Quebec, West Virginia,
Tennessee, North Carolina, Georgia.
B. columbiana Edmunds, 1960. Washington.
B. escambiensis Berner, 1955. Florida.
B. gibbera Berner, 1955. Georgia, Florida.
B. lacustris McDunnough, 1932. Ontario, Quebec, New Brunswick, Michigan,
Illinois.
B. obesa (Say, 1839) (Baetis). New Hampshire, New York, Michigan, Illinois,
Georgia, Florida, Mississippi, California (?).
B. rogersi Berner, 1940. Georgia, Alabama, Florida, South Carolina.
B. rubescens (Provancher, 1876) (Cloe). Quebec.

Berner (1940) described B. rogersi from specimens he collected
and reared in northwest Florida. Later Berner (1955) keyed the nymphs
and images of the species in his revision of the southeastern species of
Baetisca.
The relationship of B. rogersi to other species in the southeast will
not be fully understood until the nymphs and images of all species are
known and studied. Berner (1940) pointed out that B. rogersi appears
to be related to B. carolina and based this conclusion on similarities in
male genitalia and wing coloration of the images, the absence of dorsal
spines on the mesonotum of the nymphs, and the similarity of mouth-
parts in the nymph.
Later Schneider and Berner (1963) described a new speices, B. becki,
and suggested it was most closely related to B. rogersi based upon
morphological similarities of the nymphs. Schneider and Berner (1963)
gave six morphological characters to separate the nymphs, but Pescador
and Peters (1971) pointed out that the presence of ventral spots (Fig. 9
A, B) and the relatively smaller size of B. becki are the best of the key
characters delineating nymphs of B. becki from B. rogersi. Furthermore
Pescador and Peters (1971) indicated that body size, color pattern, and
structure of the male genital forceps are good characters to delineate the
images of these two species. We agree with Schneider and Berner
(1963) that B. becki and B. rogersi are closely related.
Little is known about the ecology and habits of B. becki. Schneider
and Berner (1963) collected nymphs from swift-flowing, shallow, sand
bottom streams with a constant pH of 5.4 in March and May; the nymphs
lived into June. We have collected nymphs of B. becki and B. rogersi
in April and May and adults of both species in May from the Blackwater
River, Okaloosa County, Florida.
The known distribution of B. becki is extreme northwestern Florida.
B. rogersi occurs throughout northwest Florida, southeastern Alabama,


1974







BULLETIN FLORIDA STATE MUSEUM


0.1 mm


FIGURE 9.-Ventral color patterns: A) B. rogersi; B) B. becki. Eggs of B. rogersi:
C) newly laid egg; D) mature egg.

Georgia, and western South Carolina (Fig 6 A). New range extensions
are from the following localities: Georgia, Cherokee Co., upper Etowah
River at St. Route S-2551, E. T. Hall; and South Carolina, Oconee Co.,
Chattooga River at Hwy. 76, 26 June 1971, P. H. and N. F. Carlson.

LIFE HISTORY AND ECOLOGY
In order to study in detail the ecology and seasonal distribution of
Baetisca rogersi, the various life history stages (eggs, nymphal instars,
subimagos, and images) must be determined and described and the
habits and habitats of each stage must be known. Because of the
extreme difficulty in conducting life history studies in the stream environ-
ment, hearings were completed only in the laboratory.

THE EGGS
EXTERNAL MORPHOLOGY
Mature egg (Fig. 9 C,D): Diameter 0.2-0.3 mm; opaque white;
spherical without polar caps; chorion smooth, with no sculpturing; attach-
ment structures consist of networks of sticky fibers on surface of chorion.


Vol. 17, Io. 3







PESCADOR AND PETERS: BAETISCA ROGERSI


TABLE I.--NUMBER OF DAYS FOR THE Baetisca rogersi EoGG TO START HATCHING
UNDER LABORATORY CONDITIONS.

No. of
Fertilized Minimum nymphs Average
Date eggs No. of or Date of incubation water
extracted eggs unfertilized hatching time Actual % temp. C
1968
April 27 2726 unfertilized May 28 31 days 9 0.33 24.3*
April 27 2539 unfertilized May 28 31 days 41 1.61 24.3*
April 29 2137 fertilized May 19 20 days 82 3.83 24.8*
May 8 2800 fertilized May 30 22 days 21 0.76 24.2*
May 11 1590 fertilized May 31 20 days 36 2.26 24.3*
May 13 1876 fertilized June 2 20 days 26 1.39 22.1"
June 30 1721 unfertilized July 24 24 days 10 0.57 21.3"
1969
March 11 2650 unfertilized March 31 20 days 19 0.72 21.3*
March 28 2600 fertilized April 20 23 days 151 5.92 22.0*
April 1 2551 unfertilized April 28 27 days 38 1.48 22.0*
Average no. days unfertilized= 26.6
Average no. days fertilized=21.0

Mature eggs flatten when in clumps or clusters on the bottom of an
incubation dish. The sticky nature of the egg surface probably serves
to attach them securely to the substratum of the stream. Smith (1935)
studied the eggs of B. obesa and B. carolina and also found a smooth
chorion without sculpturing. Newly laid eggs of B. rogersi are subspheri-
cal with average measurements of 0.1 mm X 0.2 mm (Fig. 9 C). The
eggs are yellowish-white with a colorless chorion and contain a large
mass of yolk. The change in egg shape from subspherical to spherical
(Fig. 9 D) took place approximately 3-5 hours after oviposition. Com-
pacting within the reproductive organs of the female images probably
accounts for their subspherical shape on oviposition. Egg color changed
from yellowish to opaque-white 9-12 hours after oviposition.

INCUBATION PERIOD

As shown in Table 1, the time required for eggs to begin hatching in
the laboratory (water temperatures 200 to 32.20 C) ranged from 20-31
days. The percentage of nymphs hatched was quite low for both the
fertilized and unfertilized eggs compared with results of other workers
(Degrange 1960, Elliott 1972). We did not have temperature control
equipment, and suspect our results would have been quite different if
we had. Bohle (1968) gives an account of morphogenesis in eggs of
Baetis rhodani (Pictet) and B. vernus Curtis, and shows the effects of
temperature on development in different stages. Our laboratory data


1974






BULLETIN FLORIDA STATE MUSEUM


A""














", / "Ir--_














third instar; D) fourth instar.

scarcely begin to show the possibilities inherent for development in may-
fly eggs, nor will it account for the seasonal pattern of nymphal instars of
Baetisca rogersi (Tables 3 and 4) discovered in field work.
Fertilized eggs averaged 21.0 days while unfertilized eggs required
an average of 26.6 days to begin hatching. Degrange (1960), who also
found that unfertilized eggs took longer to hatch in six European species


Vol. 17, No. 3







PESCADOR AND PETERS: BAETISCA ROGERSI


of other genera, attributed the longer incubation period to delays and
irregularities at the beginning of segmentation in the embryonic develop-
ment.
The eggs did not all hatch at once. The duration of hatching in
the laboratory extended from 7-17 days. As the eggs often formed
clusters or clumps in the bottom surface of the dish, the eggs in the
center of the cluster might obtain less oxygen. In nature, the eggs
probably drift downstream far enough to be well dispersed. Attachment
surfaces for the eggs are certainly plentiful on the rough stream bottom.

THE NYMPHS

EXTERNAL MORPHOLOGY
We found 12 nymphal instars in Baetisca rogersi. A set of mor-
phological characters distinguish the first 11 instars, and all 11 descrip-
tions are consistent and comparable. The twelfth instar nymphs are de-
scribed fully. Recognizable differences between male and female nymphs
first occur in the sixth instar. All characters described refer to both
males and females unless otherwise noted.
First Instar Nymphs (Fig. 10 A): Body Length 0.40-0.60 mm; width of head
0.09-0.14 mm; thoracic notal shield: length 0.09-0.14 mm, width 0.15-0.19 mm;
caudal filaments 0.05-0.07 mm. Head: opaque white, anterior margins smooth and
dome-shaped. Compound eyes black and subspherical. Three ocelli present, all
small, grayish, pale near margins. Antennae subequal to 1/2 length of head, 4-seg-
mented, segment 2 longer than segments 1, 3, and 4 combined. Thorax: dorsum
of thorax with transparent semirectangular notal shield which covers the entire sur-
face of pronotum and metanotum; anterior margin of thoracic notal shield a little
concave and smooth, lateral and posterior margins bare and a little convex; dorsal
surface fiat and bare. Legs: opaque; pro-, meso-, and metathoracic legs similar;
femora cylindrical and bare; tibiae 1-segmented with a long spine on inner margin
near apex; tarsi with a long spine on inner median margin; claws long, slender, with-
out denticles. Abdomen: 10 visible tergal segments; first 5 segments subequal in
length, compact, combined length equal to 1/3 total length of abdomen; postero-
lateral covers of terga 6-9 angular. Caudal filaments: whitish and bare; 4 short
visible segments; apex of each filament thread-like, median filament a little longer
than cerci.
Newly hatched nymphs were very active. First instars were colorless and opaque,
and the whole body was filled with yolk globules. Immediately after eclosion, the
young nymphs started to move either by crawling or swimming freely with strong
undulations of the abdominal segments and caudal filaments.
Molting occurred 2-4 days after eclosion, the duration of the first instar averaging
3.2 days.
Second Instar Nymphs (Fig. 10 B): Body length 0.65-0.85 mm; width of head
0.15-0.20 mm; thoracic notal shield: length 0.13-0.21 mm, width 0.20-0.27 mm;
caudal filaments 0.08-0.12 mm. Head: opaque white; a little flattened; frontal
process a little developed with the anterior margins smoothly arched. Compound
eyes a little larger than those of the first instar nymphs. Ocelli more prominent and
slightly darker than those of first instar nymphs. Antennae whitish, 4-segmented
with segment 2 greatly elongated. Thorax: posterior margin of metanotum over-
lapping abdominal segments 1 and 2; anterior margin of the thoracic notal shield a


1974







BULLETIN FLORIDA STATE MUSEUM


little concave and smooth; anterolateral corners angular; lateral and posterior mar-
gins bare and a little convex; median carina of thoracic notal shield indistinct. Legs:
color, shape, and structure as in first instar. Abdomen: opaque; abdominal tergal
segments 1 and 2 partially fused; posterolateral covers of segments 6-9 more de-
veloped and sharply pointed than those of first instar nymphs; segment 9 elongated
and cylindrical. Caudal filaments: color and number of segments as in first instar
nymphs; median filament subequal to cerci.
Ecdysis of the second instar occurred after 3-5 days.
Third Instar Nymphs (Fig. 10 C); Body length 0.90-1.30 mm; width of head
0.23-0.29 mm; thoracic notal shield: length 0.30-0.48 mm, width 0.60-0.80 mm;
caudal filaments 0.30-0.39 mm. Head: pale white; anterior margin of frontal process
a little curved near base of antennae. Compound eyes: inner margin angular, facets
clearly defined. Ocelli more distinct, prominent, larger than those of the second
instar nymphs. Antennae: grayish-white. Thorax: posterior margin of thoracic
notal shield truncate, extending to near posterior margin of abdominal segment 5,
median carina distinct and more prominent than in second instar nymphs, devoid of
elevations. Legs: whitish; shape and structure as in second instar nymphs. Abdo-
men: whitish; tergal segments 1 and 2 fused; gills 1 and 2 present; pyramidal struc-
ture on tergum 6 weakly developed; posterior margin of tergum prominently ex-
cavated to receive the small rounded anterior margin of tergum 10; small dorsal
tubercles at mid-posterior margin of terga 7-9 and appear as simple elevations; pos-
terolateral spines present on segments 6-9. Caudal filaments: color and structure of
filaments as in second instar nymphs.
Duration of the third instar is unknown as all nymphs died in the laboratory.
Fourth Instar Nymphs (Fig. 10 D): Body length 1.40-1.80 mm; width of head
0.30-0.50 mm; thoracic notal shield: length 0.55-0.70 mm, width 0.80-1.20 mm;
caudal filaments 0.30-0.40 mm. Head: pale white; genae well developed; frontal
process extends anteriorly and almost overlaps the anterior margin of head. Com-
pound eyes: inner margin sharply angulated. Ocelli larger than those of third in-
star, black. Antennae: pale white; 5-segmented. Thorax: thoracic notal shield pale
white, uniformly washed with light brown along median line; median carina more
distinct than that of third instar nymphs, devoid of elevations as in third instar
nymphs; a small black macula on submedian surface; anterolateral corners with a
distinct notch; lateral spines present and appear as simple lateral projections; poster-
ior margin with long hair, a little truncate near the median carina and elevated into
a roof-like structure. Sternum of thorax washed uniformly with brown. Legs: pale
yellow; small spines present inner margins of tibiae and tarsi; outer margins covered
with long hairs; tarsal claws more curved than those in third instar. Abdomen:
abdominal gills 1-4 present; abdominal terga 1-6 whitish; pyramidal structure of ab-
dominal segment 6 excavated along its median surface and lies in the excavation of
the posterior margin of the thoracic notal shield; abdominal terga 7-10 pale yellow;
small, weakly developed, dorsal median projections on terga 7-9; posterolateral spines
on segments 6-9, spines on segment 9 curved inwardly embracing tergum 10. Sterna
1-6 washed uniformly with brown, sterna 7-10 pale yellow; subanal plate triangular
apically. Caudal filaments: pale yellowish; apical 2/3 thickly fringed with hairs.
The duration of the fourth instar is unknown. All nymphs in this stage were
collected in the study areas, and molted after 2-5 days in the laboratory.
Fifth Instar Nymphs (Fig. 11 A): Body length 1.80-2.30 mm; width of head
0.50-0.70 mm; thoracic notal shield: length 0.80-1.20 mm, width 1.30-1.90 mm;
caudal filaments 0.50-0.80 mm. Head: light brown, with uniform, minute black
stipplings; a prominent black spot below base of compound eyes near lateral margins
of head; a small frontal prominence present below frontal projection of the head;
genae greatly extended anterolaterally. Compound eyes: triangular with inner and
outer posterolateral corners angular. Ocelli smaller in relation to size of compound
eyes than those in the fourth instar nymphs. Antennae: color and number of seg-
ments as in the fourth instar nymphs. Thorax: thoracic notal shield yellowish-brown,


Vol. 17, No. 3






1974 PESCADOR AND PETERS: BAETISCA ROGERSI 169

A /.. /C\ ..',


I:C 1
/;"- ", '
?. .- /


/, (( # ,,


CI D
-._ ,.:



... /. i
.IT-,' r %, :' ' .,.




I "' \ .-- \ D .. 1-.


\ ( .* /,
S -_--i-/ \J
C'7 '/ .

t 1 f'
,. % .*..,^ r..

,, ') ^ "
i il I '

\,-\ It
f,, i/ :f

|!i i v



FIGURcE 11.-Nymphal instars of B. rogersi: A) fifth instar; B) sixth instar; C)
seventh instar; D) eighth instar.








BULLETIN FLORIDA STATE MUSEUM


entire shield with uniform, minute, black stipplings; two small elevations present
along median carina; paired dorsal submedian spines near posterior 1/3 of shield;
anterolateral corners notched to receive head; lateral spines more distinct and prom-
inent than those of fourth instar nymphs; lateral extensions distinct. Sternum yellow-
ish-brown. Legs: color pattern as in fourth instar nymphs except lateral margins
brown; shape and structure of legs as in fourth instar nymphs. Abdomen: abdominal
gills 1-6 present; abdominal terga 1-5 pale; base of pyramidal projection of tergum
6 brown; terga 7-10 pale yellow; small median knob-like projections on terga 7-9;
median line of terga 7-9 brown, except projections pale; posterolateral spines on seg-
ments 6-9. Abdominal sterna 1-6 yellowish brown, remainder of segments pale;
subanal plate triangular apically. Caudal filaments: basal 1/3 of caudal filaments
grayish-brown, remainder pale yellow; apical 2/3 of caudal filaments fringed with
long hair, remainder bare.
The fifth instar molted after 10-12 days, averaging 11.5 days.
Sixth Instar Nymphs (Fig. 11 B): Body length of male 2.30-3.40 mm; width of
head 0.60-0.90 mm; thoracic notal shield: length 1.20-1.70 mm, width 1.90-3.10
mm; caudal filaments 0.60-1.19 mm. Body length of female 2.30-3.50 mm; width of
head 0.60-1.00 mm, thoracic notal shield: length 1.20-1.90 mm, width 1.90-3.00
mm; caudal filaments 0.60-1.18 mm. Head: color and markings as in fifth instar
nymphs, except dark brown macula more prominent near anterior base of compound
eyes; anterior projection of frontal process of head poorly developed; shape of frontal
prominence of head as in fifth instar nymphs; genae greatly expanded with antero-
lateral corners distinctly angular. Compound eyes: black; inner posterolateral cor-


B


FIGURE 12.-Hind wing pad development of nymphal instars of B. rogersi: A) sixth
instar; B) seventh instar; C) eighth instar; D) ninth instar; E) tenth instar; F)
eleventh instar; G) twelfth instar.


Vol. 17, No. 3


AP








PESCADOR AND PETERS: BAETISCA ROGERSI


ners of eyes of females rounded. Size and shape of lateral ocelli as in fifth instar
nymphs; median ocellus smaller than lateral ocelli. Antennae: pale, 6-segmented.
Thorax: thoracic notal shield light brown with uniform minute black stipplings; ele-
vation of median carina greatly produced and prominent; paired dorsal spines distinct
and subequal in length to posterior elevation of median carina; anterolateral corners
brown, spinous; lateral spines well developed, sharply pointed, brown at apex; size
of lateral extensions of notal shield as in fifth instar nymphs. Hind wing pads poorly
developed, lobe-like as in Figure 12 A. Sternum light brown, darker at lateral mar-
gins. Legs: yellowish-brown; a dark brown macula near base of dorsal surface of
tibiae; tarsi with a median transverse brown band, inner margins with one row of
small spines. Abdomen: terga 1-5 pale, tergum 6 light brown, anterolateral margins
of each segment dark brown; mid-dorsal elevations on terga 7-9 prominent, pale;
posterolateral spines present on segments 6-9. Abdominal sterna 1-6 brown, re-
mainder of segments pale; a brown macula present near anterolateral corners of
sterna 7-9; subanal plate triangular apically. Caudal filaments: basal 1/3 and apical
1/2 of caudal filaments brown, remainder paler; apical 2/3 of caudal filaments fringed
with long hairs.
Ecdysis of the sixth instar occurred in 11-14 days, averaging 12.5 days.
Seventh Instar Nymphs (Fig. 11 C): Body length of male 3.10-4.40 mm; width
of head 0.90-1.30 mm; thoracic notal shield: length 1.70-2.40 mm, width 2.50-4.20
mm; caudal filaments 0.80-1.50 mm. Body length of female 3.20-4.50 mm; width of
head 1.00-1.40 mm; thoracic notal shield: length 1.70-2.40 mm, width 2.80-4.20
mm; caudal filaments 0.80-1.50 mm. Head: light brown except posterolateral areas
near base of compound eyes brown; a transverse ridge present between compound
eyes near posterior margins of vertex; a prominent black macula near anterior base
of compound eyes; anterior projection of frontal process of head more prominent than
that of the sixth instar nymphs; basal 1/3 of frontal prominence overlapped dorsally
by frontal projection of head; anterolateral corners of genae angular. Compound
eyes: grayish-black; eyes of males larger than those of females with the inner poster-
olateral corners of eyes of females smooth and rounded. Size and shape of lateral
ocelli as in sixth instar nymphs. Antennae: pale; 6-segmented. Thorax: thoracic
notal shield light brown with distinct black tubercles; elevation of median carina more
developed than that of the sixth instar; dorsal spines prominent and cone-shaped;
anterolateral corners brown and spinous; posterior 2/3 of lateral margins of shield
crenulate, more prominent near base of lateral spines; basal 2/3 of margins of lateral
spines serrate; lateral extensions a little more distinct and prominent than those of
the sixth instars. Hind wing pads small with three distinct longitudinal tracheae as in
Figure 12 B. Sternum light brown; lateral margins darker. Legs: color pattern as
in sixth instar nymphs except for the presence of minute brown stipplings on coxae,
trochanters, and femora of prothoracic, mesothoracic, and metathoracic legs; a dis-
tinct dark brown macula near base of dorsal surface of tibiae; inner margins of tibiae
and tarsi with one row of small spines; apex of tarsal claws reddish-brown. Ab-
domen: abdominal terga 1-5 pale; posterolateral areas of tergum 6 brown and cov-
ered with minute hairs; a continuous dark brown median line on terga 7-10, inter-
rupted posteriorly on each tergum; anterior margins of terga 7-9 with a pair of broad,
dark brown, transverse maculae which extend almost to median line. Prominent
elevations or projections arise from mid-dorsum of terga 7-9; posterolateral spines
present on segments 6-9. Sternum covered with setae; base of setae dark brown;
sterna 1-6 brown, remainder of sterna yellowish-brown; a distinct dark brown macula
near anterolateral corners of sterna 7-9; subanal plate as in sixth instar. Caudal
filaments: basal 1/3 and apical 1/2 of caudal filaments smoky-brown, remainder pale;
posterior 2/3 with long hairs.
Molting of the seventh instar occurred in 12-15 days, averaging 13.2 days.
Eighth Instar Nymphs (Fig. 11 D); Body length of male 3.70-5.50 mm; width
of head 1.20-1.50 mm; thoracic notal shield: length 2.20-2.80 mm, width 3.20-4.70
mm; caudal filaments 1.30-1.70 mm. Body length of female 3.90-5.60 mm; width


1974







BULLETIN FLORIDA STATE MUSEUM


i


/


IX


/" VIl

VI

IV

1^11


FIGURE 13.-Lateral views of the thoracic notal shield of B. rogersi nymphs. Roman
numerals refer to nymphal instars.

of head 1.20-1.50 mm; thoracic notal shield: length 2.20-2.80 mm, width 3.50-4.60
mm; caudal filaments 1.30-1.80 mm. Head: light brown with minute black stip-
plings, a prominent transverse ridge between compound eyes near posterior margin
of vertex; a distinct black macula near anterior base of compound eyes near posterior
margin of vertex; lateral borders of genae weakly crenulated with the anterolateral
covers angular; anterior projections of frontal process of head more developed than
those of the seventh instar nymphs; basal 1/2 of frontal prominence of head dorsally
covered by the frontal process. Compound eyes: grayish-black; posterolateral cor-
ners of inner margins of eyes of males angular and larger than those of females;
inner posterolateral covers of eyes of females rounded and smooth. Ocelli black,
relatively smaller than those of the seventh instar nymphs; median ocellus equal in
size to lateral ocelli. Antennae: yellowish; 7-segmented. Thorax: thoracic notal
shield light brown with dark brown tubercles and minute black stipplings, smaller
tubercles along areas near median carina, larger tubercles around base of lateral
spines; elevation of median carina and paired dorsal spines as in Figure 13 VIII;
lateral borders of shield near base of lateral spines light brown except apex reddish-
brown; basal 2/3 of margins of lateral spines serrate; size and shape of lateral ex-
tensions as in seventh instar. Hind wing pads with numerous tracheal branches as
in Figure 12 C. Sternum light, lateral margins brown. Legs: brown except tibiae
and tarsi pale; apex of tarsal claws reddish-brown; a prominent dark brown macula
near base of dorsal surface of tibiae; tarsi with a broad, median, transverse, dark
brown band, margins with one row of small sharp spines. Abdomen: terga 1-5 pale;
posterior 1/2 of tergum 6 brown, darker around base of pyramidal structure, remain-
der of tergum pale; terga 7-10 yellowish-brown with minute dark brown setae; a


Vol. 17, No. 3


/----X1





PESCADOR AND PETERS: BAETISCA ROGERSI


A
K


I~Y


FIGURE 14.-Nymphal instars of B. rogersi: A) ninth instar; B) tenth instar; C)
eleventh instar; D) twelfth instar.


1974







BULLETIN FLORIDA STATE MUSEUM


continuous dark brown median line on terga 7-10, interrupted posteriorly on each
tergum; anterior margins of terga 7-9 with a pair of broad, dark brown, transverse
maculae extending to median line, elevations at mid-dorsum of terga 7-9 prominent
and pointed; posterolateral spines present on segments 6-9. Color and markings of
sternum as in seventh instar nymphs; submedian plate slightly cleft apically. Caudal
filaments: basal 1/3 smoky brown, remainder pale; posterior 2/3 of caudal filaments
with long brownish hairs.
The eighth instar lasted for 14-16 days, averaging 14.8 days.
Ninth Instar Nymphs (Fig. 14 A): Body length of male 4.50-6.50 mm; width of
head 1.40-1.90 mm; thoracic notal shield: length 2.70-4.30 mm, width 3.80-5.50 mm;
caudal filaments 1.40-1.50 mm. Body length of female 4.70-6.60 mm; width of head
1.40-1.80 mm; thoracic notal shield: length 2.80-4.30 mm, width 3.90-6.20 mm;
caudal filaments 1.60-2.07 mm. Head: brown with numerous minute black stipplings;
black macula near anterior base of compound eyes partly covered dorsally by the
anterolateral margins of eyes; lateral borders of genae crenulated; anterior projection
of frontal process of head greatly extended forward; basal 1/3 of frontal prominence
of head dorsally covered by the frontal process. Compound eyes: black, larger than
those of the eighth instar nymphs; shape of inner margins of posterolateral corners
of eyes of males and females as in eighth instar nymphs. Ocelli greatly reduced,
inconspicuous. Antennae: yellowish; 7-segmented. Thorax: thoracic notal shield
light brown with numerous dark brown tubercles and minute black stipplings, areas
adjacent to median carina darker in males, dark brown tubercles more abundant on
males; elevations of median carina and paired dorsal spines as in Figure 13 IX;
lateral borders of shield crenulated and serrated near base of lateral spines; basal 2/3
of margins of lateral spines serrate; lateral spines light brown except reddish-brown
at apex; lateral extensions more prominent than those of eighth instar. Hind wing
pads with longitudinal tracheae and numerous small tracheal branches (Fig. 12 D).
Sterna brown with minute dark brown setae. Legs: light brown, coxae darker, apex
of tarsal claws reddish-brown; a prominent broad dark brown macula near base of
dorsal surface of tibiae; tarsi with a broad, median, transverse, dark brown band.
Inner margins of tibiae and tarsi with one row of spines. Abdomen: terga 1-5 pale;
posterior 1/2 of tergum 6 dark brown, almost black around base of pyramidal struc-
ture, remainder pale; posterior border of tergum 6 with small black tubercles; terga
7-10 light brown with dark brown tubercles; a prominent continuous dark brown
median line on terga 7-10, interrupted posteriorly on each tergum; anterior margin
of terga 7-9 with a pair of dark brown transverse maculae extending almost to
median line; elevations at mid-dorsum of terga 7-9 pale, more prominent than those
in the eighth instar nymphs; posterolateral corners of terga 6-9 with spines. Sterna
lieht brown; lateral borders of sterna 1-6 brown with minute setae, base of setae
dark brown; sterna 1-7 with a network of black stipplings; a dark brown macula near
anterolateral corners of sterna 7-9; subanal plate cleft apically. Caudal filaments:
pale except basal 1/3 of median filament and lateral margins of cerci reddish-brown;
posterior 2/3 of caudal filaments with long brownish hairs.
The ninth instar molted after 14-16 days, averaging 15.2 days.
Tenth Instar Nymphs (Fig. 14 B): Body length of male 5.40-7.50 mm; width of
head 1.60-2.00 mm; thoracic notal shield: length 3.20-4.60 mm, width 4.60-5.90 mm;
caudal filaments 1.70-2.20 mm. Body length of female 5.70-7.50 mm; width of head
1.70-2.10 mm; thoracic notal shield: length 3.30-4.60 mm, width 4.70-6.10 mm;
caudal filaments 1.80-2.20 mm. Head: brown, except borders of genae and anterior
projections of frontal process pale; head with numerous small dark brown tubercles;
a black macula near anterior base of compound eyes, partly covered by anterolateral
margins of compound eyes; genae expanded, anterolateral corners angular and bor-
ders weakly crenulated; frontal process of head greatly extended beyond anterior
margins of head; a distinct median carina on vertex and extended anteriorly through
base of frontal process of head, continuous posteriorly to median carina of thoracic
notal shield. Compound eyes: black, larger than those of the ninth instar nymphs;


Vol. 17, No. 3








PESCADOR AND PETERS: BAETISCA ROGERSI


eyes of males larger than those of females; inner margin of posterolateral corners of
eyes of males angular; inner margin of posterolateral corners of eyes of females
rounded. Ocelli obscured and marked by the absence of black tubercles over the
area. Antennae: yellowish, 8-segmented; basal segment washed with brown. Thorax:
color and markings of thoracic notal shield of males as in ninth instar nymphs, light
brown in females except the anterior 1/2 near median carina washed with brown;
numerous dark brown tubercles; elevation of median carina and paired dorsal tuber-
cles as in Figure 13 X; lateral borders of shield crenulated, serrated at base of lateral
spines; lateral spines pale, reddish-brown at apex; margins of lateral spines serrate.
Hind wing pads as in Figure 12 E. Sterna light brown with numerous black setae.
Legs: yellowish-brown except base of coxae washed with brown; margins of legs as
in ninth instar nymphs. Abdomen: color pattern of terga 1-5 and markings of ter-
gum 6 as in ninth instar nymphs; terga 7-10 light brown with numerous setae; base
of setae dark brown, tuberculated; a prominent continuous dark brown median line
on terga 7-10, interrupted posteriorly on each tergum; anterior margins of terga 7-9
with a pair of dark brown transverse maculae that extend almost to median line;
elevations at mid-dorsum of terga 7-9 keel-shaped, approximately equal to 1/2 length
of their respective terga; lateral borders of terga 6-9 weakly crenulated, crenulation
weakest on tergum 6; posterolateral corners of terga 6-9 with spines more prominent
than those of ninth instar nymphs. Sterna light brown, lightly washed with dark
brown, with prominent black setae; sterna 1-7 with a minute network of black stip-
plings; black macula near anterolateral corners of sterna 7-9 more prominent than in
ninth instar nymphs; subanal plate more deeply cleft than that of ninth instar. Caudal
filaments: pale, except base of cerci light brown; basal 1/2 of median filament red-
dish-brown; posterior 2/3 of caudal filaments with long brownish hairs.
The tenth instar molted after 15-18 days, averaging 16.8 days.
Eleventh Instar Nymphs (Fig. 14 C): Body length of male 6.60-8.10 mm; width
of head 2.00-2.20 mm; thoracic notal shield: length 3.90-4.80 mm, width 5.50-6.10
mm; caudal filaments 2.00-2.30 mm. Body length of female 6.70-8.50 mm; width
of head 2.10-2.30 mm; thoracic notal shield: length 4.00-5:30 mm, width 5.70-6.30
mm; caudal filaments 2.00-2:40 mm. Head: color and markings as in tenth instar
nymphs; dark brown tubercles on head of females more abundant than in males;
genae expanded, anterolateral corners rounded and weakly crenulated; frontal process
of head as in Figure 14 C, a distinct median carina on vertex and extended through
base of frontal process of head, continuous posteriorly to median carina of thoracic
notal shield. Compound eyes: black, eyes of males larger than those of females, in-
ner margins of posterolateral corners of compound eyes of males as in Figure 14 C;
inner margins of posterolateral corners of compound eyes of females rounded. Ocelli
obscured. Antennae: yellowish, 9-segmented. Thorax: thoracic notal shield light
brown, with numerous dark brown tubercles, fewer tubercles in males than in fe-
males: elevations of median carina and paired dorsal spines as in Figure 13 XI;
lateral borders of shield crenulated, serrated at base of lateral spines; color and mark-
ings of lateral spines and lateral extensions as in tenth instar. Hind wing pads pale,
light brown at margins (Fig. 12 F); base of hind wing pads of nymphs reddish-
brown. Sterna light brown with small, black tuberculated setae. Legs: yellowish-
brown except coxae washed with smoky-brown; margins of legs brownish; outer sur-
face of femora with black tuberculated setae; apex of tarsal claws reddish-brown; a
prominent dark brown macula near base of dorsal surface of tibiae; tarsi with a
median, transverse, dark brown band; inner margins of tibiae and tarsi with one row
of sharply pointed spines. Abdomen: terga 1-5 pale; posterior 1/2 of tergum 6 dark
brown with black tubercles at posterior margins, almost black at basal 1/2 of pyra-
midal structure, dorsal concavities of pyramidal structure pale; terga 7-10 light brown
with numerous black tuberculated setae; a prominent continuous dark brown median
line on terga 7-10, interrupted posteriorly on each tergum; anterior margins of terga
7-9 with a pair of dark brown transverse maculae; median, dorsal elevations of terga
7-9 keel-shaped, approximately equal to 1/2 length of their respective terga; lateral


1974







BULLETIN FLORIDA STATE MUSEUM


1:>7)


/


~i' j!


I*''h-I d









FIGURE 15.-Mature nymph of B. rogersi. A-F.-Mouthparts: A, left mandible;
B, labrum; C, right maxilla, ventral view; D, hypopharynx; E, ventral (right) and
dorsal (left) view of labium; F, apex of maxilla enlarged; G-H.-Forp leg and fore
claw. I-J.-Frontal and lateral views of head of female nymph.

borders of terga 6-9 crenulated, crenulation weakest at tergum 6; posterolateral
spines on terga 6-9. Sterna light brown with numerous black tubercles; lateral mar-
gins of sterna 1-5 brown; a small network of black stipplings present near posterior
margins of sterna 1-8; size of black macula near anterolateral corners of sterna 7-9


H/


Vol. 17, No. 8








PESCADOR AND PETERS: BAETISCA ROGERSI


as in tenth instar nymphs; posterior borders of sterna 6-9 weakly crenulated; subanal
plate deeply cleft apically. Caudal filaments: cerci light brown, darker at base;
proximal 2/3 of median filament yellowish brown; distal 1/2 of caudal filaments an-
nulated; posterior 2/3 of caudal filaments with long brownish hair.
The eleventh instar molted after 16-18 days, averaging 17.6 days.
Twelfth Instar Nymphs (Fig. 14 D): Body length of male 6.80-8.90 mm; width
of head 2.00-2.50 mm; thoracic notal shield: length 4.50-4.80 mm, width 5.90-6.60
mm; caudal filaments 2.10-2.50 mm. Body length of female 7.40-9.90 mm; width
of head 2.20-2.60 mm; thoracic notal shield: length 4.30-5.70 mm, width 5.70-7.00
mm; caudal filaments 2.20-2.70 mm. Head: brown, except margins of genae and
anterior projections of frontal process of head pale; head with numerous black tuber-
cles; genae expanded, anterolateral covers of genae crenulated; anterior projection
of frontal process of head as in Figure 14 D and 15 I, J. Compound eyes: grayish-
black; eyes of males larger than females, almost occupying the entire dorsal area of
the head. Ocelli obscured. Antennae: pale, basal segments darker; 9-segmented;
antennal socket ringed with brown. Mouthparts (Fig. 15 A-F): labrum light brown
(Fig. 15 B). Outer surface of mandibles with brownish papillae; left mandible as
in Figure 15 A; molar surface of mandibles with 12-14 teeth; a sclerotized reddish-
brown projection at base of molar area. Maxillae pale, except pectinate spines and
teeth at distal margin of galea-lacinia reddish-brown; shape of pectinate spines and
teeth of distal margin of galea-lacinia as in Figure 15 C,F; segment 2 of maxillary
palpi subequal a little longer to 1 1/4 length of segment 1; segment 3 of palpi sub-
equal in length to segment 2, apex acute; hair on maxillae as in Figure 15 C. Lingua
of hypopharynx oval with minute setae along anterior margins; superlingua of hypo-
pharynx as in Figure 15 D, with a row of long hairs along anterior margin. Labium
light brown, except glossae darker: segment 2 of labial palpi 2/3 length to a little
shorter than segment 1; segment 3 of palpi 1/3 length of segment 2; inner margin of
distal corer of segment 2 finger-like; glossae as in Figure 15 E, anterior margin with
minute hair, inner surface of glossae near distal margin with pectinate hairs; para-
glossae as in Figure 15 E, with long hairs at lateral and anterior borders, inner sur-
face of paraglossae near distal margin with spine-like hairs as in Figure 15 E. Thorax:
thoracic notal shield brown, with numerous black tubercles, notal shield of males
with fewer dark brown tubercles than those of the females; elevation of median
carina and dorsal spines of thoracic notal shield as in Figure 13 XII, lateral borders
of notal shield crenulated, serrated at base of lateral spines; lateral spines yellowish-
brown at apex; lateral projections of notal shield as in Figure 14 D. Hind wing nadq
as in Figure 12 F; basal 1/3 of hind wing pads of newly molted nymphs reddish-
brown, otherwise reddish-black, curled. Sterna light brown, with small black tuber-
culated setae; prosternum concave, posterior 1/4 of lateral borders indented to re-
ceive median coxal spur. Legs (Fig. 15 G,H): brownish-yellow except coxae brown-
ish; outer surface of coxae and femora with black tubercles; a prominent dark brown
macula near base on dorsal surface of tibiae; tarsi with a median, transverse, dark
brown band; inner margins of tibiae and tarsi with one row of spines; tarsal claws as
in Figure 15 H; reddish-brown at apex. Gills (Fig. 16): gill 1 as in Figure 16 A;
dorsal portion of lamella long, pointed at posterior margin; ventral portion of lamella
consists of ramified tracheal branches; tracheae grayish. Gill 2 as in Figure 16 B,
with lamella flattened and expanded; gill 2 forms a protective covering for gills 3, 4,
and 5. Gill 3 as in Figure 16 C; dorsal portion of lamella pointed at posterior mar-
gin; ventral portion of lamella consists of ramified tracheal branches arranged linear-
ly along inner lateral border. Dorsal portion of lamella of gill 4 blunt at posterior
end, tracheal branches as in Figure 16 D. Gill 5 as in Figure 16 E, shape as in gill
4. Gill 6 reduced, oval with the posterior 1/2 transparent and membranous as in
Figure 16 F; gill 6 fits exactly into the concavity formed by the surface of the pos-
terior elevation of the median carina and the dorsal groove of the pyramidal struc-
ture on tergum 6 (Fig. 20 A,B). Abdomen: terga 1-5 pale, completely concealed
under thoracic notal shield; posterior 1/2 of tergum 6 dark brown with black tuber-







BULLETIN FLORIDA STATE MUSEUM


FIGURE 16.-Gills of mature nymph of B. rogersi: A) gill 1; B) gill 2; C) gill 3;
D) gill 4; E) gill 5; F) gill 6.
cles at posterior margin; basal 1/2 of pyramidal structure of tergum 6 blackish,
dorsal surface pale; terga 7-9 light brown except margins smoky-brown; pyramidal
structure of tergum 6 well developed with the posterior face subequal to the greatest


VoL 17, No. 3







PESCADOR AND PETERS: BAETISCA ROCERSI


length of tergum 7; a prominent, continuous, dark brown, median line on terga 7-
10, interrupted posteriorly on each tergum; anterior margins of terga 7-9 with a pair
of dark-brown, transverse lines; mid-dorsum elevations of terga 7-9 pale, keel-shaped,
approximately equal to 1/2 the length of the respective terga; lateral borders of terga
6-9 crenulated; crenulation weakest at tergum 6; posterolateral corners of terga 6-9
produced into spines as in Figure 14 D; abdomen of males more flattened than those
of the females. Sterna light brown with numerous black tubercles; lateral margins of
sterna 1-5 dark brown; a small network of black stipplings near anterior and pos-
terior margins of sterna 1-8; prominent black macula near anterolateral corners of
sterna 6-9; posterior border of sterna 6-9 weakly crenulated; subanal plate deeply
cleft apically. Caudal filaments (Fig. 14 D): cerci light brown, darker at base;
basal 2/3 of median filament reddish-brown; remainder of filament brown; posterior
2/3 of caudal filaments with long brownish hair.
The twelfth instar molted after 17-21 days, averaging 17.6 days.

GROWTH AND DEVELOPMENT
We reared the first three nymphal instars of Baetisca rogersi from
eggs hatched in the laboratory. Instars four through twelve came from
young nymphs collected in. the field and reared individually in the
laboratory. The fourth instar identification was based on body length,
head width, and degree of development of the thoracic notal shield.
Although admittedly little research has been completed on other
species, this represents the lowest total number of instars reported in
the Ephemeroptera. Ide (1935b) estimated a total of 30-45 instars
for Stenonema canadense (Walker) and about 30 instars for Ephemera
simulans Walker. Murphy (1922), rearing small groups from eggs, found
27 stadia (apparently all nymphal instars) in Baetis posticatus (Say).
Rawlinson (1939) reared and classified 17 developmental stages in
Ecdyonurus venosus (Fabricius). These morphological stages did not
correspond to instars in this species but occurred independently at
different instars. However, from information on the Palmen organ of
two young (6 mm) nymphs, Rawlinson stated that the minimum possible
number of molts was 16. Degrange (1959) reared 43 nymphs of
Cloeon simile Eaton from egg to imago; the number of molts (including
the subimaginal molt) varied from 21-30. Degrange was also able to
correlate successfully the number of layers in the Palmen organ with
the number of molts. Finally, applying Dyar's rule to a laboratory
population, Froehlich (1969) calculated a total of 15-16 nymphal in-
stars for Caenis cuniana Froehlich.
The data indicate a total of 12 nymphal instars in B. rogersi. No
alternate method of estimating the number was made. Dyar's rule is
a geometric growth ratio; its calculation requires a large population
reared under constant conditions. Lacking necessary technical equip-
ment, we made no attempt to dissect the Palmen organ. An undiscovered
instar might conceivably exist between the third and fourth instars. Also


1974







BULLETIN FLORIDA STATE MUSEUM


TABLE 2.-DURATION OF NYMPHAL INSTARS OF Baetisca rogersi UNDER LABORATORY
CONDrnONS.

Minimum-maximum Average
Instal No. no. days duration duration
I 37 2-4 3.2
II 22 3-5 4.2
III 2 died after 2 days ?
IV 4 collected in field- ?
2-5 days
V 4 10-12 10.7
VI 4 11-14 12.5
VII 5 12-15 13.2
VIII 5 12-16 14.8
IX 6 14-16 15.2
X 6 14-18 16.8
XI 8 16-19 17.6
XII 7 17-21 19.1


nymphal growth under natural conditions, being much more prolonged
than laboratory growth, could involve additional instars; however this
appears unlikely in B. rogersi. Further, as Degrange (1959) conclusively
demonstrated, instars from eggs of one female reared under identical
conditions can have different numbers of molts. Nevertheless, we shall
refer to 12 instars of B. rogersi as they are distinct and recognizable.
Table 2 shows the minimum, maximum, and average durations of
nymphal instars reared in the laboratory, except for the third and
fourth instar nymphs. The duration of the later instars is longer than
that of the earlier instars; average duration increased progressively from
the first to second and from the fifth to twelfth instars. Although there
was no record of the duration of the third and fourth instars, we estimate
that each of these instars require no more than 10 days. Therefore the
approximate length of nymphal development of B. rogersi in the
laboratory is about 4 months.
We collected nymphs in the study area from September through
early July. Collecting continued through the summer unsuccessfully.
The earliest record of young nymphs was 20 September 1968 and the
nymphs were in the fourth instar based on size and external features.
The eggs probably hatched in early September. In the laboratory in-
cubation time of the eggs ranged from 20-31 days averaging 23.8 days,
and hatching continued for 7-17 days. If the same length of time is re-
quired to hatch eggs in the field, then those laid in March should have
hatched in April and May. However diapause and dormancy at high and
low temperatures have been demonstrated in Ephemeroptera eggs (Bohle
1968). Although no experimental work was done with B. rogersi, we


Vol. 17, No. 3







1974


PESCADOR AND PETERS: BAETISCA ROGERSI

HEAD WIDTH IN MILLIMETERS


0 0.2 0.4 0,6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6

NOVEMBER, 1967
01 :1. . ..11 1 11111
S# FEMALES

3
3 # # MALES El 1 DECEMBER, 1967
3 #FEMALES
6-

3 JANUARY, 1968 # MALES
3 # FEMALES





9-r
6
3 FEBRUARY, 1968 # MALES
0
3- # FEMALES
9-
6
3 MARCH, 1968 # MALES
0 . .i. . . .
3 # FEMALES
6
9

6-
3 APRIL, 1968 # MALES

3 # FEMALES F

9


S' 1 Y, 19 68 # 2MALES2 2 2
# FEMALES
JUNE, 1968 # MALES
-# FEMALES

0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2 2,4 2,6

FIGURE 17.-Size-frequency distribution of B. rogersi nymphs collected at Rocky
Comfort Creek, 1967-1968.







182 BULLETIN FLORIDA STATE MUSEUM Vol. 17, No. 8

HEAD WIDTH IN MILLIMETERS
0 0,2 0.4 0.6 0,8 1.0 1.2 1.4 1,6 1,8 2.0 2.2 2.4 2.6

3 I # SEX (?) SEPTEMBER, 1968

3-
0- --- ....1 ,,,,p m, #, MALES OCTOBER, 1968

#E #SEX (?),f. # # MALES NOVEMBER, 1968
3- # FEMALES
3- # MALES DECEMBER, 1968
3 J # FEMALES

3 JANUARY, 1969 # MALES

3 # FEMALES

3 FEBRUARY, 1969 # MALES

3Z #FEMALES

3 MARCH, 1969 # MALES

3 # FEMALES


6 APRIL, 1969
3 # MALES
0 a E.. PR
3 # FEMALES ": ..

6--
3 MAY, 1969 # MALES

3 #FEMALES
6

3 JUNE, 1969 # MALES

0 0.2 0.4 0.6 0.8 1.0 1,2 1,4 1,6 1.8 2,0 2,2 2,4 2,6
FIcURE 18.-Size-frequency distribution of B. rogersi nymphs collected at Rocky
Comfort Creek, 1968-1969.







PESCADOR AND PETERS: BAETISCA ROGERSI


TABLE 3.-SEASONAL DISTRIBUTION, EXPRESSED BY NUMBER OF NYMPHAL INSTARS
COLLECTED PER MONTH, OF Baetisca rogersi N ROCKY COMFORT CREEK,
1967-68.
Date 1 9 6 7 1 9 6 8
Instar Sep. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug.
I 1421 761 101
II 191 31
III 11
IV
V 1
VI 4 2
VII 2 13 1 1 1
VIII 8 10 4 7 1 1
IX 5 12 13 9 3 1
X 1 4 5 10 1
XI 1 4 1 9 5 1
XII 1 41 43 2 1

'Laboratory reared specimens only which may not reflect field conditions.

surmise that most eggs did not hatch until temperatures cooled in the
fall, and the hatching continued for more than 17 days. The variability
and fluctuation of natural stream conditions should prolong hatching
beyond those times recorded in the laboratory. Ide (1935a), noting
that eggs of Stenonema canadense hatched over a period of 6 weeks,
assumed that different incubation times for the eggs are genetically
based.
Nymphs that did hatch in April were probably killed by the high
temperatures and low oxygen content of the water (Figs. 7, 8). Newly
hatched nymphs reared in the laboratory at 22.20-23.90 C died after
one molt. When water temperatures were lowered to 18.90-21.10 C and
other variables remained the same, the nymphs lived longer, an indication
that temperature is important in survival of early instar nymphs. Ide
(1935a) believed that eggs of certain mayfly species remain dormant
during summer and those that hatch early are killed by high temperature.
Also the low oxygen content of the stream water in summer (Fig. 8) is
probably detrimental to the early instar nymphs.
Size measurements of nymphs included total body length, exclusive
of caudal filaments, and head width. From these measurements total
range of nymphal body length was 0.40 mm for the first instar to
8.80 mm (male) and 9.90 mm (female) for the twelfth instar. Head
width ranged from 0.09 mm for the first instar to 2.50 (male) and 2.60
(female) for the twelfth instar.
Figures 17 and 18 give size-frequency distributions of B. rogersi


1974







BULLETIN FLORIDA STATE MUSEUM


TABLE 4.-SEASONAL DISTRIBUTION, EXPRESSED BY NYMPHAL INSTARS COLLECTED
PER MONTH, OF Baetisca rogersi IN ROCKY COMFORT CREEK, 1968-69.

Date 1 9 6 8 1969
Instar Sep. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug.
I 81 1541 431 471
II 30x 11 21
III 1
IV 4 2
V 1 2
VI 1 4 2 1
VII 4 3 2 4 4 1 3
VIII 1 5 13 1 1 5 2
IX 1 2 6 4 4 5 5
X 3 3 7 3
XI 3 2 6 6 2 1
XII 1 12 1152 572 212 22

'Laboratory reared specimens only which may not reflect field conditions.
2Total includes nymphal exuvia of subimagos observed emerging in field.

based on head width of nymphs collected in the field. We used head
width because we found it to be the least variable index of growth.
For the 1968-1969 season, nymphs collected in September had head
widths of 0.30-0.50 mm. Nymphs collected in October had head widths of
0.80-1.30 mm, in November 0.40-1.70 mm, in December 1.00-1.50 mm,
reaching in March and April widths of 2.50-2.60 mm (Fig. 18). No in-
crease in maximum width occurred after April. Results for the 1967-
1968 season were similar (Fig. 17) as were the seasonal distributions of
the instars (Tables 3 and 4).
Low temperatures probably accounted for the slow growth of the
nymphs during December. Cold temperatures were first recorded in
November (Fig. 7). They dropped to a low of 50 C in December and
January and apparently reduced nymphal feeding, slowing nymphal
growth. As the water warmed in late January (Fig. 7), the nymphs grew
rapidly. Many authors have given similar results. In a study of the
factors influencing the life histories of some species of mayflies in
Alberta, Hartland-Rowe (1964) reported that no growth occurred in
nymphs of Epeorus longimanus (Eaton), Ephemerella inermis Eaton,
and E. lapidula McDunnough during the period when the stream tem-
perature was 00 C. Harker (1952) reported that the growth rate
of Ecdyonurus torrentis Kimmins dropped from November to February
when the temperature was below 6 C. Similarly, Moon (1939) found
that no growth took place in winter for nymphs of Caenis horaria (L.).
In fact reduction in and absence of overwinter growth are generally


Vol. 17, No. 3







PESCADOR AND PETERS: BAETISCA ROGERSI


TABLE 5.-SEASONAL VARIATION IN SIZE OF LAST INSTAR NYMPHS OF Baetisca
rogersi COLLECTED IN ROCKY COMFORT CREEK.

Males Females
Date Body length mm Head width mm Body length mm Head width mm
Collected Range Mean Range Mean Range Mean Range Mean
1968
March 7.30-8.90 8.07 2.10-2.40 2.26 7.60-9.90 9.05 2.20-2.60 2.42
April 7.20-8.40 7.68 2.10-2.40 2.17 7.40-9.60 8.63 2.10-2.50 2.32
May 6.70-8.00 7.36 1.90-2.30 2.13 7.40-8.90 8.00 2.10-2.30 2.10
June' 7.20 7.20 2.10 2.10
1969
March 7.90-8.60 8.31 2.20-2.40 2.30 8.50-9.30 8.90 2.30-2.50 2.40
April 6.90-8.60 8.00 2.00-2.40 2.26 8.20-9.60 8.81 2.10-2.40 2.35
May 6.40-8.00 7.37 2.00-2.20 2.12 7.40-9.00 8.34 2.10-2.50 2.47
June' 7.30 7.30 2.00 2.00
'Only one specimen.


recognized phenomena, which Landa (1968) classifies as Al (reduced
growth) and A3 (no growth) in his characterization of developmental
cycles of European Ephemeroptera.
We classified nymphs from the monthly field collections to instar by
comparing them morphologically to those known nymphal instars reared
in the laboratory (Tables 3 and 4). The size range of instars from the
field varied more than those from the laboratory. Nymphs from the field
were generally larger in body size, reaching a maximum body length
of 8.9 mm (males) and 9.9 mm (females) compared to 8.0 mm (males)
and 8.6 mm (females) for those reared in the laboratory. Also, the
range of body size of the different instars from the monthly collections
overlapped. For example the body length of eleventh instar males ranged
from 6.6-8.1 mm compared to 6.8-8.9 mm for twelfth instar males; the
same phenomenon occurred in females. A possible explanation for size
overlap is that larger nymphs may be physiologically younger than
smaller nymphs (Clifford 1970), or nymphs of the same stage may ex-
hibit different growth rates as Hunt (1953) found in Hexagenia limbata
(Guerin).
The average size of last instar nymphs collected in May and June
was smaller than that of last instars collected in March and April (Table
5). Similar findings were reported by Gledhill (1959) for Ameletus
inopinatus Eaton, Minshall (1967) for Epeorus pleuralis (Banks), and
Clifford (1970) for Leptophlebia cupida (Say). Following these authors,
the larger B. rogersi nymphs collected in March would be those that
overwintered half-grown; last instar nymphs in May and June would


1974







BULLETIN FLORIDA STATE MUSEUM


TABLE 6.-SuBSTRATUM PREFERENCES OF THE NYMPHS OF Baetisca rogersi.

Total
Trial Type of bottom 12 hr. 36 hr. 48 hr. No. %
A (stony) 7 13 12 32 71.1
I B (sandy) 1 1 2 4 8.9
C (leaf-litter) 7 1 1 9 20.0
A (stony) 12 14 13 39 86.7
II B (sandy) 0 1 1 2 4.4
C (leaf-litter) 3 0 1 4 8.9
A (stony) 10 13 15 38 84.4
III B (Sandy) 2 1 0 3 6.7
C (leaf-litter) 3 1 0 4 8.9

A (stony) 29 40 40 109 80.7
Total B (sandy) 3 3 3 9 6.7
C (leaf-litter) 13 2 2 17 12.6


be those that achieved most of their growth in spring, thus maturing
faster. Favorable water temperatures (Fig. 7) an increased supply
of diatoms (Table 8), and increased photoperiod are probably the
major factors accelerating nymphal growth in spring (Thibault 1971).
In summary, although laboratory data show that B. rogersi could
support two or more generations each year, only one occurs in north
Florida. Thus unknown factors prolong the life cycle, delaying hatching
or young nymph development until fall and slowing nymphal over-
winter growth. We agree with the conclusions of other workers, most
recently Thibault (1971), that while temperature is not the only factor
regulating the length of the life cycle, it is among the most important.
For B. rogersi, temperature (Fig. 7), oxygen (Fig. 8), and food supply
(Table 8) appear significant; we did not investigate photoperiod.

HABITAT AND HABITS

Mature Baetisca rogersi nymphs in Rocky Comfort Creek were
typical members of a lithophilous association, living in the exposed,
stony substratum of the sampling station. Younger nymphs, the fourth
through seventh instars, lived only in areas with a thick growth of
filamentous algae and water moss (Spirogyra sp. and Leptodictyum
riparium). Also as nymphs approached emergence they moved to
quiet, shallow sections of the stream. This move to a quiet area may be
associated with the search for objects or places to leave the stream and
emerge.
The habitat of the nymphs in Bear Creek was similar. Most early


Vol. 17, No. 3







PESCADOR AND PETERS: BAETISCA ROGERSI


TABLE 7.-INFLUENCE OF LIGHT ON SUBSTrATUM PREFERENCES OF NYMPHS OF
Baetisca Rogersi.

12 hours 36 hours 48 hours Total
Trial Type of bottom Light Dark Light Dark Light Dark Light Dark
A (stony) 4 3 15 15 7
I B (sandy) 0 11 0 11 0
C (leaf-litter) 11 1 0 11 1
A (stony) 5 5 15 15 10
II B (sandy) 0 10 0 10 0
C (leaf-litter) 10 0 0 10 0
A (stony) 14 3 2 14 5
III B (sandy) 0 12 0 12 0
C (leaf-litter) 1 0 13 13 1

No. 35 10 33 12 43 2 111 24
Totals
T% 77.8 22.2 73.3 26.7 95.5 4.5 82.2 17.8


instar nymphs were collected in a thick mat of L. riparium along the
submerged concrete wall of the bridge. Larger or older individuals
frequented the underside of submerged logs or partially buried them-
selves in the sand along the shallow edges of the stream.
In the laboratory eighth through twelfth instar nymphs preferred
a stony substratum, but when this was not provided they partially buried
themselves in the sand or firmly attached themselves along the covers
of the aquarium. Nymphs also congregated on a plastic screen stretched
along the inside of the aquarium.
In a laboratory experimental study on habitat preference, light and
stony substratum significantly influenced the distribution of the nymphs.
We conducted two experiments as explained in Methods. In one experi-
ment a tray with three substrata was exposed to light. Combined results
of three trials showed an average of 80.7% of nymphs studied were
found in Section A with stony bottom, 6.7% in Section B with sandy
bottom, and 12.6% in Section C with a substratum composed of leaf
litter (Table 6, Fig. 19 A). In trial I, 71.1% of the nymphs moved to
Section A, 86.7% in trial II, and 84.4% in trial III.
In a further experiment we exposed one section of the tray to light
while the other two sections were covered. Fifteen nymphs were used
in each of three trials. Results are shown in Table 7 and Figure 19 B.
Section C (leaf litter) was lighted while Section A (stones) and Section
B (sand) were covered. After 12 hours 11 (73.3%) of 15 nymphs
occupied Section C (light, leaf litter), 4 (26.7%) Section A (dark,
stones), and none Section B (dark, sand). Then Section B was lighted.







BULLETIN FLORIDA STATE MUSEUM


ABC ABC ABC
TRIAL I TRIAL II TRIAL III
A


A IB C B A C C AB
LIGHT K DARK LIGHT DARK

B


FIGURE 19.-Importance of substratum and light on habitat preference of B. rogersi
nymphs: A shows %of nymphs frequenting a substrate when all are in light; B
shows % of nymphs on each substrate when one substrate is in light and the others
are dark. Substrates are stony (A), sandy (B), or with leaf-litter (C).

Results show 11 (73.3%) nymphs were found in Section B, 3 (20%) in
Section A (dark, stones), and 1 (6.7%) in Section C (dark, leaf-litter).
When Section A (stones) was lighted, all of the nymphs (100%) moved
to this section. Similar results were obtained in trials II and III. A
majority of the nymphs confined themselves to the lighted division of the
tray regardless of the type of substratum. Light appears to be more
significant than substratum in influencing the habitat choice of B. rogersi
nymphs. The fact that a few nymphs remained in the stony bottom
portion of the tray even when dark suggests that the nature of the
stream bed and light combined influence the distribution of nymphs in
the stream. Hughes (1966b) reported a number of mayfly species
that exhibit the same light response but offered no explanation as to
the mechanism involved.
Current also limited the distribution of B. rogersi nymphs in the
stream. Nymphs were usually in running water. Those in quiet portions
of the stream were last instar nymphs and their presence was probably
associated with their search for objects or places to emerge.
The nymphs of B. rogersi are morphologically adapted for life in
flowing water. Their tarsal claws (Fig. 15 H) are heavily sclerotized,
curved, and sharply pointed, enabling them to hold firmly to objects in
the substratum. The thoracic notal shield with its dorsal elevations
and dorsal and lateral spines apparently helps decrease resistance to
current. Hora (1930) suggested that spines on blepharocerid larvae are
developed as a means of diminishing resistance to strong current; the
spines create a layer of calm water against the body of the larva.


Vol. 17, No. 3







PESCADOR AND PETERS: BAETISCA ROGERSI


Nymphs were not active during the day. They usually stayed under
rocks, or partially buried in the sand. When at rest, the last three
abdominal segments are bent dorsally with the caudal filaments over the
body. In the laboratory, we sometimes saw the nymphs wave their
caudal filaments in a steady up and down motion. This beating probably
aids respiration by creating a water current. Other possible reasons
for such movements are: they help the nymphs maintain balance and
position, or they clean silt and debris from the nymphs' bodies.
Newly collected nymphs brought to the laboratory were positively
phototactic. In an experimental study on the dorsal light response, the
nymphs exhibited "somersaulting" behavior. "Somersaulting" is a term
used to describe the light-orientation response displayed by many aquatic
invertebrates. When a light is directed into a container from the side,
nymphs swim with the dorsal surface to their body towards the light and
the ventral surface away. After passing the light they return to their
normal orientation. This behavior resembles a loop or a "somersault."
In a further experiment, we covered an aquarium with black paper,
leaving only one small spot of light. Nymphs crawled to and congregated
at the light. When this light spot was moved under the aquarium,
nymphs tried to dig down, head first, to it. Evidently the position of
the light source has a very marked influence on the maintenance of the
primary dorsoventral orientation of the nymphs. Hughes (1966a)
postulated that the dorsal light response of Baetis harrisoni Barnard is
initiated by the ocelli and maintained by the compound eyes. He further
stated that the ocelli are only transparent to light and therefore only a
very small response is elicited. Whether the same explanation could be
offered for the nymphs of B. rogersi needs further investigation.
Nymphs remained motionless when touched. As their coloration
closely resembles their habitat, such behavior has apparent survival
value.
The swimming activities of various species of Baetisca nymphs have
been described by Walsh (1864), Traver (1931), and Berner (1950).
Our observations of the movement of B. rogersi nymphs agree with
those given by Berner (1950). Nymphs swim by the vigorous and rapid
undulation of the last three abdominal segments including the caudal
filaments. The legs are drawn under the body with the prothoracic legs
oriented forward and with the tibiae and tarsi at right angles to the
femora. The mesothoracic and metathoracic legs are directed posteriorly.
As the nymphs come to rest the legs spread and seize any available
supporting object. The legs are not used in the actual process of swim-
ming. The force that initiates swimming apparently comes from the last
three abdominal segments. These are bent upward with the caudal


1974







BULLETIN FLORIDA STATE MUSEUM


i 2 5

.... ... .. \ \
... ....





FIGURE 20.-Gill position of mature B. rogersi nymph: A) lateral view; B) dorsal
view of gill apices and abdominal segments 5-6.

filaments held over the body. A sudden return to their normal position
followed immediately by continued upward and downward beats provides
momentum. Nymphs often float for a period of time before swimming
movements begin. After the nymphs leave the substratum they swim
vigorously for a while and then dive downward to reach the bottom
quickly.
To investigate Bemer's (1940) theory lateral spines of the thoracic
notal shield of Baetisca act as balancers, we removed these spines. With-
out them the nymphs could not balance themselves, or could just barely
maintain a normal position for a short time before turning over. Further-
more, the nymphs could not maintain direction. Instead of swimming
forward as they normally do, a zigzag pattern occurred and the nymphs
were limited to a short distance. Evidently the lateral spines do stabilize
the nymphs in the water as Berner suggested. The spines perform a
similar function in B. rogersi's alternate habitat, stabilizing the nymphs
in moving sand. Spines also reduce current resistance, as previously
discussed.
The abdominal gills of B. rogersi are completely enclosed under the
thoracic notal shield, apparently for protective purposes. The gills
are used for respiration, a process we studied in living nymphs. The
notal shield raised and lowered in a rhythmic fashion enabling water
to circulate inside the gill chamber. Water flowed into the cavity
through a space between the lateral edges of the thorax. Inflow of water
occurred during the upward stroke of the notal shield; when the notal
shield returned to its normal position, water flowed out from the cavity.
We removed the thoracic notal shield to study gill movements (Fig.
20 A). The gills exhibited simple upward and downward strokes. The


Vol. 17, No. 3







PESCADOR AND PETERS: BAETISCA ROGERSI


TABLE 8.-RELATIVE ABUNDANCE OF GUT CONTENTS OF NYMPHS OF Baetisca rogersi
COLLECTED IN ROCKY COMFORT CREEK, NOVEMBER 1968 TO MAY 1969.

Total no. % Fila- % %
of items % % mentous Mineral Arthropod
Month counted Detritus Diatoms algae particles remains
Nov. 312 51.28 17.63 2.24 28.85 0.00
Dec. 308 51.63 13.96 2.27 32.14 0.00
Jan. 198 59.09 10.61 1.01 29.29 0.00
Feb. 277 44.77 33.21 11.19 10.83 0.00
Mar. 378 46.56 36.24 0.53 15.61 1.06
Apr. 423 55.32 37.35 0.71 6.62 0.00
May 401 53.37 17.95 0.25 28.43 0.00


upward motion was more or less directed sideward with the downward
stroke a simple return to normal position. As water flows from the
cavity, the small plate-like gills of the sixth abdominal segment snugly
join together and form a tube that fits into the circular space between the
posterior elevation of the notal shield and the concave dorsal surface
of tergum 6 (Fig. 20). The sixth abdominal gills serve as a channel for
the discharge of water from the cavity.
The nymphs of B. rogersi are detritivorous. Examination of 21
nymphs revealed the dominant gut components as detritus, diatoms,
mineral particles, and a few fragments of filamentous algae (Table 8).
Identified diatoms were Navicula sp., Surirella sp., Nitzschia sp., Meridion
sp., Pinnularia sp., Fragilaria sp., and Gomphonema sp. One desmid,
Micrasterias sp., was also found. Among the recognizable filamentous
algae were Spirogyra sp., Cladophora sp., and Oedogonium sp. We also
found a few fragments of arthropod remains in one specimen, but these
were probably ingested accidentally. Although alimentary tracts of both
large and small nymphs collected throughout the season were examined,
no significant differences were discernible in the composition of materials
eaten by the various instars. We did note an increase in abundance of
diatoms among dissected nymphs collected in February, March, and
April, when a thick population of diatoms covered the rocks in the
stream. Nymphs of many mayfly species feed on diatoms, algae, and
organic debris as reported most recently by Minshall (1967) and Coff-
man, Cummins, and Wuycheck (1971).
The nymphs feed at night. In the laboratory they browsed on the
surface of rocks and crawled back and forth on the substratum apparently
feeding. Sometimes they bit off pieces of water moss. While feeding
the nymphs alternately raked the substratum towards the mouthparts
with the tibiae and tarsi of the prothoracic legs. The nymphs also
placed their prothoracic legs between the mouthparts apparently re-


1974







BULLETIN FLORIDA STATE MUSEUM


moving food particles. Attempts to study the movements of the mouth-
parts while feeding were unsuccessful.
Many of the ninth through twelfth instars rested on the plastic screen
in pairs, one on top of the other. At first we thought the nymphs were
copulating because of their position and, in each case, the pair con-
sisted of a male and female. Careful observations, however, proved our
assumption incorrect. Some of the paired nymphs were dissected and
their reproductive organs examined under the microscope. The female
reproductive organs were not well developed and male sperm were
immature. Twelfth instar females did have mature ovaries, but ex-
tracted eggs did not hatch. The significance of this paired behavior
remains unknown.
In the laboratory, nymphs of the twelfth instar crawled up to the
surface of the water and attached themselves on the plastic screen
along the edge of the aquarium with the dorsum of the head exposed
above the water surface. This behavior occurred only a few minutes
prior to emergence.

ASSOCIATED ORGANISMS
We preserved and identified all macro-organisms collected with
Baetisca rogersi during the weekly samplings. These collections reveal
not only the diversity of the faunal composition, but also offer a better
understanding of the ecological community in which B. rogersi lives.
Most of the organisms associated with it were arthropods, mainly insects.
A list follows.

Crustacea
Decapoda Astacidae Procambarus spiculifer (Le Conte)
Isopoda Asellidae Asellus sp.
Arachnoidea
Hydracarina Athienemanniidae Krendowskia sp.
Insecta
Ephemeroptera Siphlonuridae Isonychia sp. A of Berner
Isonychia sp. B of Berner
Baetidae Baetis spiethi Berner
B. spinosus McDunnough
B. intercalaris McDunnough
Heptageniidae Stenonema exiguum Traver
S. smithae Traver
Stenonema sp.
Metretopodidae Siphloplecton speciosum Traver


Vol. 17, No. 3








PESCADOR AND PETERS: BAETISCA ROGERSI


Leptophlebiidae


Ephemerellidae



Tricorythidae
Neoephemeridae
Caenidae



Baetiscidae
Aeschnidae
Gomphidae


Libellulidae
Calopterygidae
Coenagrionidae
Pteronarcidae
Nemouridae


Perlidae







Megaloptera Sialidae
Corydalidae


Haliplidae
Gyrinidae
Elmidae


Trichoptera Psychomyiidae


Hydropsychidae


Leptophlebia intermedia (Traver)
Leptophlebia sp.
Paraleptophlebia volitans (McDunnough)
Ephemerella (s.s.) choctawhatchee Berner
E. (Dannella) simplex McDunnough
E. (Dannella) sp.
E. (Eurylophella) trilineata Berner
Tricorythodes albilineatus Berner
Neoephemera young Bemer
Brachycercus maculatus Berner
Brachycercus sp.
Caenis hilaris (Say)
C. diminuta Walker
Baetisca obesa (Say)
Boyeria vinosa (Say)
Gomphus (s.s.) minutus Rambur
G. (Stylurus) ivae Williamson
Progomphus obscurus (Rambur)
Macromia sp.
Calopteryx maculata (Beauvois)
Argia moesta (Hagen)
Pteronarcys nobilis Hagen
Taeniopteryx maura (Pictet)
Taeniopteryx sp.
Acroneuria sp.
Neoperla clymene (Newman)
Neoperla sp.
Perlinella drymo (Newman)
Perlinella sp.
Perlesta placida (Hagen)
Perlesta sp.
Phaganosphora capitata (Pictet)
Sialis sp.
Chauliodes rastricoris (Rambur)
Nigronia serricomis (Say)
Haliplus sp.
Dineutes sp.
Stenelmis convexula Sanderson
Macronychus glabratus Say
Nytiophylax sp.
Phylocentropus placidus (Banks)
Hydropsyche orris Ross
Cheumatopsyche pinaca Ross


Odonata









Plecoptera


Coleoptera







BULLETIN FLORIDA STATE MUSEUM


Leptoceridae Athripsodes angustus (Banks)
A. cancellatus (Betten)
A. nephus Ross
A. transversus (Hagen)
Oecetis persimilis (Banks)
Diptera Tipulidae Tipula abdominalis (Say)
T. (Yamatotipula) caloptera Loew
T. (Yamatotipula) sp.
Chironomidae Ablabesmyia mallochi (Walley)
Cricotopus bicinctus (Meigen)
Cricotopus sp.
Metriocnemus lundbeckii Johannsen
Polypedilum (s.s.) sp.
Procladius culiciformis (L).
Tanytarsus sp.
Simuliidae Simulium sp.

In addition to the arthropods, several species of fish lived near the B. rogersi
nymphs habitat. Species of fish collected were pirateperch (Aphredoderus sayanus),
brown darter (Etheostoma edwini), gulf darter (E. swaini), mosquitofish (Gambusia
affinis), yellowbelly sunfish (Lepomis auritus), lowland shiner, (Notropis cumming-
sae), sailfin shiner (N. hypselopterus), speckled madtom (Noturus leptocanthus),
blackbanded darter (Percina nigrofasciata). A mole salamander, Ambystoma sp.,
was also collected in the study area.

Mayfly nymphs have long been known as an important food of fresh-
water fish. The gut contents of fish examined from the study areas con-
tained undigested leg segments and mandibles of mayflies, but all were
too decomposed to be identified positively to species.
Figure 21 gaves a list of mayfly species associated with nymphs of
B. rogersi indicating the seasonal succession of the mayfly fauna in the
habitat.
Twice we found pupae of Simulium sp. attached to the median
posterior half of the dorsal surface of the thoracic notal shield of B.
rogersi, but larvae so attached we never found. The Simulium may have
mistaken quiet B. rogersi nymphs for stones. The small percentage in-
cidence (< 1%) of attached pupae suggests only a fortuitous association.

THE SUBIMAGOS
EXTERNAL MORPHOLOGY
Male Subimagos (live specimens) (Fig. 2): Body length 6.3-8.2 mm; fore wings
8.0-9.2 mm; caudal filaments 5.3-6.9 mm. Head: grayish-brown, darker at posterior
margin of vertex; dorsal surface of genae near base of compound eyes grayish-yellow;
frons grayish except adjoining areas surrounding the ocelli brownish. Antennae:
pale, basal segment washed with brown; antennal socket including basal segment
grayish-brown; remainder of segments pale. Compound eyes grayish-yellow. Ocelli
pale yellow, reddish-brown at base. Thorax: pronotum narrow, grayish-brown ex-
cept median line pale. Mesonotum grayish-brown, covered with fine black stipplings;


Vol. 17, No. 3







1974 PESCADOR AND PETERS: BAETISCA RO

J F M A M J

ISONYCHIA sp. A of Berner i 900!000000 0-1-
ISONYCHIA sp. B of Berner +-4 + + + + +
BAETIS INTERCALARIS +----+ + + + +
B. SPIETHI Po.10 9 p10 0 0 0 0
B. SPINOSUS i0 0 0 on 00 0 i 0 0 0
SIPHLOPLECTON SPECIOSUM i -i0"00001 + +
STENONEMA EXIGUUM ggo 0 00 0o9 go 0 10 0 9go0 9o
S. INTERPUNCTATUM .o i 0,0 00o0 .o Opo0 0 0o
S. SMITHAE 0 0 00 09O 01 0100 0 10 0,0 0C0
STENONEMA sp. +- + + + + +
LEPTOPHLEBIA INTERMEDIA --- I I + + +
LEPTOPHLEBIA sp. I I I + + +
PARALEPTOPHLEBIA VOLITANS **-i00900900-9900*99
EPHEMERELLA (SS,) i ooo 00 o0 o 0 oO o
CHOCTAWHATCHEE
E. (DANNELLA) SIMPLEX t 010 0000-0 0t1 09
E. (DANNELLA) sp. I I I I + +
E. (EURYLOPHELLA) TRILINEATA 1 i-- 10 0 "* P
TRICORYTHODES ALBILINEATUS 0 0 0 o 0 pes 0*1* O
TRICORYTHODES sp. + + + + + + +
NEOEPHEMERA YOUNG I i 0 10 00 +
BRACHYCERCUS MACULATUS + + + i i !
CAENIS DIMINUTA + i!0 a000.00. 0
C. HILARIS + + + -- I
BAETISCA OBESA i, p00 90 0p npP +


IGERSI 195

J A SO ND



+
+ n--i-i-i-n



o 0 00 0 0o O 02 ,0 o 1 0 0 90


001000 o0 090 0 o0 C 0o 0 9o



+ + + + I--4
+ + + + +--4
+ + + + -I-


+ + + -+-------+



+ + + + + +
+ + + -I----+--



+ + ---+--V
- ----1 00i00] 00 0




+ I- I I


00o Imagos, subimagos, and fully mature nymphs
-- Nymphs
FIGURE 21.-Seasonal distribution of Ephemeroptera species associated with B. rogersi
at Rocky Comfort Creek.

parapsidal furrows reddish-brown, anterior 1/3 of inner parapsidal furrows flexed
inwardly towards median line to form an irregular M-shaped marking on mesonotum;
median line of mesonotum pale, mesoscutellum saddle-shaped with a distinct macula
near the anterolateral margin, mesoscutellum grayish-brown, darker at margins and
blackish at posterolateral margins, posterior margin truncated. Metanotum grayish-







BULLETIN FLORIDA STATE MUSEUM


FIGURE 22.-Ventral view of male genitalia of B. rogersi subimago.


brown; posterior 1/2 of metanotum membranous, covering entirely abdominal seg-
ment 1. Pleural areas of pronotum dark grayish-brown; epimeron and episternum
of mesothorax and metathorax including the axillary sclerites reddish-black, remain-
der of pleuron grayish. Prosternum grayish, submedian projections grayish-brown,
and extend beyond posterior bases of fore coxae; mesosternum and metasternum gray-
ish-yellow; ventral extensions of pleuro-trochantin near basisternum smoky brown.
Furca of mesosternum and metasternum ringed with dark brown. Basisternum and
metasternum covered with fine black stipplings. Legs: pale yellowish-brown except
dorsal surface of coxae washed with dark grayish-brown; dorsal surface of each tar-
sal joint with a black transverse band at apex; dorsum of fore claws brown, venter
pale; ratios of segments in male forelegs 1.62:1.00(0.80 mm):0.59:0.36:0.35:0.18:
0.46; mesothoracic and metathoracic legs 1.41:1.00(0.81 mm):0.18:0.18:0.14:0.43.
Wings (Fig. 2): longitudinal and cross veins of fore and hind wings grayish-brown, in-
terrupted by whitish tranverse white spots throughout; posterior margins of fore wings
bordered with short brownish hair; margin of hind wings bordered with short brown-
ish hair; basal 2/3 of membrane of hind wings reddish-brown, remainder of mem-
brane grayish-brown. Abdomen: tergum 1 pale, and entirely concealed under the
membranous posterior 1/2 of metanotum of thorax; terga 2-3 short, reddish-brown,
darker at lateral and posterior margins; prominent pale spiracular openings on terga
1-6; terga 6-9 light reddish-brown, darker at posterior and lateral margins on seg-
ments 6-8; prominent dorsal elevation on posterior 1/2 of tergum 6 heavily marked
with fine black stipplings, prominent median line on terga 7-10; posterolateral spines
of terga 6-8 weak, prominent on 9; anterior margin of terga 7-10 of most male subi-
magos covered with whitish granulations. Sterna 1-8 yellowish-gray, darker at
lateral margins; sternum 9 pale; presence of fine black stipplings near anterior and
posterior margins of sterna 1-8; lateral borders of sterna 1-5 produced into small pad-
like structures overlapping each other; posterolateral margins of sterna 7-9 produced
into projections, elongated into spines on sternum 9. Genitalia (Fig. 22): genital
forceps and penes yellowish-white; forceps 3-segmented, segment 1 stout, shorter
than segment 2; inner margin of segment 2 prominently curved near basal 1/3; apical
segment small, and conical; penes triangular, subequal in length to the basal segment
of forceps; basal 2/3 of penes fused. Caudal filaments: cerci yellowish-brown, pale


Vol. 17, No. 3








PESCADOR AND PETERS: BAETISCA ROGERSI


TABLE 9.-HouRLY EMERGENCE OF Baetisca rogersi SUBIMAGOS AT ROCKY COMFORT
CREEK, 1969.

Time of emergence


<00 O-<0 -i-0e' 0 P "t.I
Dt CO M O o C CO O C c,4 Atmospheric
0Date -o SS l cS condition

partly
April 12 9 16 9 4 1 1 200 240 60% 2-3 cloudy
April 14 0 13 10 3 0 0 20* 26* 70% 5-8 clear
April 19 3 3 4 4 4 0 19" 24* 45% 3-5 clear
May 5 0 2 4 4 0 1 19" 26* 35% 2-4 clear
May 12 3 7 5 2 1 0 19* 28" 43% 3-5 clear
partly
May 25 2 3 2 2 0 0 21" 31" 68% 5 cloudy
June 12 4 3 5 2 1 3 22* 32* 45% 2 cloudy
July 4 2 0 0 0 0 0 26* 33* 35% 3 clear

Total 23 47 39 21 7 5

at apex; basal 2/3 of cerci with brown annulations at articulations; basal 1/2 of
median filament reddish-brown, remainder hyaline.
Female Subimagos (live specimens): Body length 7.0-9.3 mm; fore wings 8.9-
11.0 mm; caudal filaments 5.3-5.9 mm. Head: dark brown with black markings
along median area of vertex; color of dorsal surface of genae near base of compound
eyes as in male subimagos; frons dark brown except adjoining areas surrounding
ocelli brownish. Compound eyes smaller than in male subimagos, grayish-yellow.
Ocelli grayish-yellow, reddish-brown at base. Color and markings of antennae as in
male subimagos. Thorax: color pattern as in male subimagos except inner parapsidal
furrows and median notal suture darker; prosternal projection more separated and
shorter than in male subimagos; mesosternum and metasternus covered with network
of fine black stipplings markedly prominent on basistemum of mesothorax; meso-
thorax and metathorax including the posterior margin of abdominal segment 1 and 2
of some specimens covered with whitish granulations. Legs: color pattern as in male
subimagos. Ratios of segments in fore legs 1.25:1.00(1:00 mm):0.21:0.21:0.12:0.34;
mesothoracic and metathoracic legs 1.43:1.00(0.87 mm):0.17:0.17:0.13:0.41. Wings:
color and markings of fore and hind wings as in male subimagos. Abdomen: color
of tergum 1 as in male subimagos; terga 4-6 purplish-brown, almost black near pos-
terior margin. Dorsal elevation of tergum 6 less pronounced than in male subimagos;
color pattern of terga 7-10 as in male subimagos. Abdominal sterna covered with
black reticulations, markedly prominent near anterior margins of 6-9. Posterior mar-
gin of sternum 9 concave forming a bifid subanal plate with a deep V-shaped median
cleft (Fig. 25 C). Caudal filaments: color pattern of cerci as in male subimagos;
basal 1/2 of median filament light reddish-brown, remainder pale.
EMERGENCE
The subimagos of Baetisca rogersi emerged from the stream from
8:30 AM to 2:30 PM as Table 9 shows. Most of the subimagos emerged


1974







BULLETIN FLORIDA STATE MUSEUM


TABLE 10.-TIME REQUIRED FOR Baetisca rogersi SUBIMACOS TO EMERGE FROM
NYMPH.

Time Time Total
emergence emergence no. of
Date commenced completed minutes
Laboratory:
2.V.1968 3:10 PM 3:15 PM 5
2.V.1968 3:15 PM 3:21 PM 6
6.V.1968 2:33 PM 2:41 PM 8
12.V.1968 1:54 PM 1:58 PM 4
13.V.1968 1:40 PM 1:48 PM 8
19.V.1968 1:14 PM 1:20 PM 6
20.IV.1969 11:50 AM 12:00 PM 10
Field:
11.IV.1969 10:50 AM 10:55 AM 5
14.IV.1969 10:33 AM 10:41 AM 8
14.IV.1969 11:55 AM 12:01 PM 6
19.IV.1969 10:28 AM 10:35 AM 7
Average = 6.63


before noon with the emergence peak between 8:30 AM and 10:30 AM.
Table 9 also shows a general decrease in the number of emerging sub-
imagos toward the end of the emergence season.
Subimagos in the laboratory emerged from 10:00 AM to 8:30 PM,
a few hours later than in the field. In 1968 the earliest emergence time
was 10:00 AM and the latest 7:50 PM, whereas in 1969 times ranged
from 11:00 AM to 8:30 PM. For both years the peak time of laboratory
emergence occurred between 12:00 PM and 3:00 PM.
B. rogersi emerges above the water surface, which makes it easy to
record the time required for the emergence process (Table 10). The
time ranged from 4 to 10 minutes, averaging 6.63 minutes. We noted
no significant difference between subimagos emerging in the field and
in the laboratory. The range of 4 to 10 minutes was probably caused
by individual variability, the more vigorous individuals requiring less
time to emerge.
Emerging nymphs crawl completely out of the water. At Rocky
Comfort Creek they crawled 1 to 4 inches above the surface of the
water to a point just above the wet portion of the stumps (Fig. 23).
In places without objects sticking from the water, we have found
nymphal skins or exuviae attached just above the wet portion of the
stream bank. In the laboratory the nymphs crawled 1 to 2 inches above
the surface of the water on the strips of plastic screen. Occasionally
nymphs emerged on the screen with the apical third of their caudal
filaments still in the water, a phenomenon never observed in the field.


Vol. 17, No. 3






1974 PESCADOR AND PETERS: BAETISCA ROGERSI 199





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III
'., \
'i I










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^"4








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1 'I j \


i I :i \
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/, I .
"; ^
-^,A


FIGURE 23.-Flight pattern of B. rogersi subimago.







BULLETIN FLORIDA STATE MUSEUM


The distance that the nymphs crawl above the water surface appears to
be related to the wave action (splash condition) of the water. Nymphs
emerging in the field crawled farther above the water to find a dry sur-
face than did those in the laboratory.
The emergence process began with a small medial split of the tho-
racic notal shield. The abdominal segments contracted repeatedly in
a peristaltic fashion followed by the outward bulging of the thorax until
the entire middle medial line of the mesothoracic notal shield opened.
The split gradually progressed anteriorly and posteriorly. Anteriorly it
reached the vertex of the head, usually between the compound eyes
along the obscured ecdysial line, but sometimes extended to the base of
the frontal process of the head. Posteriorly the split terminated at the
posterior margin of the median carina. As the split progresed, the sub-
imago wriggled out from the old skin. The dorsum of the subimaginal
thorax emerged first, followed by the compound eyes and then the head.
At this point the emerging subimago assumed a slanted position with
the head and anterior half of the thorax completely exposed, and the
abdomen still encased in the old cuticle. Quick jerky body movements
and abdominal contractions completed the process with the release of the
abdominal segments and caudal filaments. Sometimes the subimago
spread out its prothoracic legs immediately upon exposure and firmly
anchored the claws on the supporting objects. This probably helped the
emerging subimago pull itself from the nymphal skin. Normally the
prothoracic legs and the mesothoracic legs remained firmly drawn under
the venter of the thorax until the metathoracic legs appeared and all
three pairs spread out at the same time. At emergence the wings of the
subimago were moist and often curled at the apex.
A newly emerged subimago remains motionless for awhile, and then
crawls up on the supporting object. This resting behavior probably
allows the subimago time to regain its strength and dry its wings.

FLIGHT ACTIVITIES
The subimagos of B. rogersi have a unique flight pattern (Fig. 23).
They dive to the water surface and then fly vertically up into the air.
The functional significance of this behavior remains unknown. The
subimagos are strong flyers, flying up out of sight in a few seconds.
Their ability to fly fast perhaps helps them avoid predators.

DURATION
The duration of the subimaginal stage of B. rogersi at laboratory
temperatures ranged from 11 hr 50 min to 30 hr, averaging 21 hr. 21 min.


Vol. 17, No. 3







PESCADOR AND PETERS: BAETISCA ROGERSI


TABLE 11.-DURATION OF SUBIMAGOS OF Baetisca rogersi AT DIFFERENT TEMPER-
ATURES.

Air
Temp. Average
C Number Range of duration (hours) Duration
19.4-20.6 6 15 hr 30 min-34 hr 23 hr 44 min
21.1-22.2 9 17 hr 5 min-30 hr 24 hr 26 min
25.5-26.7 4 16 hr 55 min-23 hr 30 min 19 hr 38 min
27.2-28.3 4 11 hr 50 min-25 hr 50 min 18 hr 57 min


Although individual variations occurred, higher temperatures seemed
to shorten the subimaginal stage. Table 11 includes only those subi-
magos for which exact durations are known. No experimental work was
done, but these observations support Lyman's (1944) conclusion that
temperature controls the length of the subimago stage.
Relative humidity in the laboratory ranged from 33% to 77%, and did
not appear to affect the subimagos' duration.

MOLTING
The molt from subimago to imago required 8 to 11 minutes and
averaged 9 min 45 sec for five laboratory specimens. The mechanism
was similar to subimaginal emergence from nymphs, except that the
ecdysial line of the head vertex split first, followed by the median dorsal
line of the thorax. The head appeared first, then the thorax. Finally
the imago pulled the abdomen, wings, and caudal filaments from the
subimaginal skin with strong undulations of the body.

PREDATION
Spiders on tree stumps where nymphs emerged preyed upon the sub-
imagos. On several occasions, the senior author saw spiders seize newly
emerged subimagos. Most of the subimagos were able to escape by
beating their wings strongly. Birds also preyed upon the subimagos.
The amount of subimago mortality from predation is unknown, but
the color pattern of B. rogersi appears to provide excellent camouflage.
The mottled pattern of the wings obscures the red spot (conspicuous in
the images) and breaks up the outline of the wings. Newly emerged
subimagos were difficult to recognize when motionless on the tree stumps.

THE IMAGES
EXTmNAL MORPHOLOGY
Male Imagos (live specimens) (Fig. 1): Length: Body 6.5-8.6 mm; fore wings


1974






BULLETIN FLORIDA STATE MUSEUM


iC
/7,

4-






D




1I m--f-~~






G
H H


FIGURE 24.-Male imago of B. rogersi: A) fore wing; B) hind wing; C) fore claw;
D) dorsal view of abdominal segment 10 and base of caudal filaments; E) ventral
view of genitalia; F) dorsal view of penes; G) prothoracic leg; H) mesothoracic leg;
1) metathoracic leg.


Vol. 17, No. 3








PESCADOR AND PETERS: BAETISCA ROGERSI


8.0-9.5 mm; caudal filaments 5.5-7.0 mm. Head: dark brown, orange near base of
ocelli, blackish at posterior margins of vertex, vertex with whitish granulations in
some specimens; dorsal surface of genae near base of compound eyes grayish-yellow;
frons grayish except adjoining areas surrounding ocelli brownish-yellow. Antennae:
pale, basal segments washed with brown; antennal socket and pedicel brown, seg-
ment 2 lighter, remainder of segments pale. Compound eyes grayish-yellow with
very minute stipplings. Ocelli yellowish-white, yellowish-orange near base. Thorax:
pronotum narrow, dark brown except median line pale; mesonotum gravish-brown,
darker at median area; mesonotum with minute black stipplings; parapsidal furrows
reddish-brown, with whitish granulations in some specimens; mesoscutellum saddle-
shaped, reddish-brown, darker at margins, blackish at posterolateral corners. Metano-
tum membranous, entirely covering abdominal segment 1. Pleural areas of pronotum
dark brown; epimeron and episternum of mesothorax and metathorax including the
axillary sclerites reddish-black, remainder of pleuron grayish. Prosternum brown,
submedian projections dark brown, and extended beyond posterior bases of fore
coxae; mesosternum and metasternum grayish-yellow; ventral extension of pleuro-
trochantin near basisternum smoky brown; basisternum covered with whitish gran-
ulations in some specimens; sutures of mesosternum and metasternum grayish with
minute black stipplings. Legs (Fig. 24 G-I): prothoracic legs pale yellowish-brown;
mesothoracic and metathoracic legs pale yellow except dorsal surface washed with
brown; dorsal surface of each tarsal segment with a brown transverse band at apex;
dorsum of fore claws brown; tarsal claws of fore legs rounded at apex (Fig. 24 C);
ratios of segments in male fore legs 1.40:1.00(1.35 mm):0.72:0.40:0.40:0.31:0.23;
mesothoracic and metathoracic legs 1.41:1.00(0.82 mm):0.21:0.21:0.14:0.43. Wings
(Figs. 1, 24 A,B): longitudinal veins of fore and hind wings amber, pale near mar-
gins; costal margins of fore wings prominently emarginated, thickened; basal 1/3 of
fore wings reddish-brown; humeral area grayish. Apex of hind wings a little obtuse;
basal 3/4 of hind wings reddish-brown. Abdomen terga 1-5 reddish-brown, darker
at margins; prominent pale spiracular openings on terga 1-6; terga 6-9 light reddish-
brown, darker at posterior and lateral margins on segments 6-8; tergum 10 as in
Figure 24 D, yellowish; prominent dorsal elevation on posterior 1/2 of tergum 6
strongly marked with fine black stipplings; sterna 1-8 grayish-white, darker at lateral
margins; sternum 9 pale, presence of fine black stipplings near anterior and posterior
margins; lateral borders of terga 1-5 reduced into a small pad-like structure; postero-
lateral margins of sterna 7-9 with projections, elongated into spines on sternum 9.
Genitalia (Fig. 24 E,F): genital forceps and penes yellowish-white; forceps 2-seg-
mented, distal 1/2 of segment 1 prominently curved; apical segment small, conical;
penes triangular (Fig. 24 F), proximal 2/3 fused. Caudal filaments: cerci yellowish-
brown, pale at apex; basal 2/3 of cerci with brown annulations at articulations; basal
1/2 of median filament reddish-brown, remainder of filament hyaline.
Female Imagos (live specimens): Length: Body 7.5-9.2 mm; fore wings 9.0-11.0
mm; caudal filaments 5.0-5.4 mm. Head: dark brown with black markings along
median area of vertex; color pattern of dorsal surface of genae near base of compound
eyes as in male images; vertex with whitish granulations in some specimens. Frontal
area of head as in Figure 25 A. Compound eyes smaller than in male images, gray-
ish-yellow; ocelli yellowish, reddish-brown at base. Color and markings of antennae
as in male images. Lateral areas of head as in Figure 25 B. Thorax: color pattern
of thorax as in male images; inner parapsidal furrows and median carina of thoracic
notal shield darker. Prosternum dark brown, submedian process shorter and more
widely separated than in male images. Legs: femora of prothoracic legs yellowish-
brown, remainder of legs light brown, markings of fore legs as in male images; color
pattern of mesothoracic and metathoracic legs as in male images. Ratios of segments
in female fore legs 1.17:1.00(0.96 mm):0.21:0.21:0.17:0.34; mesothoracic and meta-
thoracic legs 1.42:1.00(0.96 mm):0.18:0.18:0.13:0.37. Abdomen: color pattern of
abdomen as in male images, except terga 1-5 of some individuals darker. Sterna 4-7
with dark brown median line in some specimens; posterior margin of sternum 9 con-







BULLETIN FLORIDA STATE MUSEUM


FIGURE 25.-Female imago of B. rogersi: A-B) frontal and lateral view of head; C)
ventral view of ninth abdominal sternite.

cave forming a bifid subanal plate with a deep V-shaped median cleft (Fig. 25 C).
Caudal filaments: color pattern of cerci as in male images; basal 1/2 of median fila-
ment reddish-brown; remainder pale.

FLIGHT AcrwTrrms
Since Berner (1940) first described Baetisca rogersi, no one has seen
the images swarming or in flight. The images probably swarm in com-
panies or individually at a very high altitude, as do many mayfly species.
Repeated attempts to find swarming or mating images in the field were
fruitless.
Similarly we have never seen female images laying eggs, and most
species of mayflies show specific oviposition behavior. B. rogersi females
may lay eggs at night or they may migrate upstream to oviposit.

LIFE SPAN
Imagos of B. rogersi lived from 8 hr 30 min to 28 hr 20 min in the
laboratory, averaging 21 hr 8 min. Within the relatively small laboratory
variations, temperature and relative humidity had no demonstrable ef-
fect on life span. Specimens exposed to more or less the same temper-
ature and humidity lived for varied times, with some individuals living
almost four times longer than others. This life span range could be a
result of biological variation among individuals, or of unnoticed damage
to some of the specimens after emerging. No significant differences in
life span existed between males and females.

PARTHENOGENESIS
Viviparity and parthenogenesis occur in many mayflies species, but
until now neither has been reported in any species of Baetisca.


Vol. 17, No. 3







PESCADOR AND PETERS: BAETISCA ROGERSI


TABLE 12.--NUMBR OF EcGG PRODUCED BY INIVIDUAL Baetisca rogersi FEMALES.

1968 1969


Date No. of
Collected eggs


Date No. of
Collected eggs


April 27 2539 March 11 2650
April 27 2727 March 28 2600
April 29 2137 April 1 2551
May 1 2540 April 1 2021
May 3 2134 April 10 2302
May 5 1590 May 7 2400
May 8 1800 May 15 2500
May 11 1590 May 19 1500
May 13 1876
May 17 2003
June 30 1721
Average number of eggs/female=2168

1Extracted from preserved specimens.

To determine parthenogenesis, eggs extracted from an unmated fe-
male subimago on 27 April 1968 were incubated in the laboratory. Out
of a total of 2,726 extracted eggs, 9 nymphs hatched, representing ap-
proximately 0.33% (Table 1). On 30 June 1968 and 11 March 1969 we
repeated the experiment. Ten nymphs (from 1,721 eggs) and 12 nymphs
(from 2,650 eggs) hatched. On 1 April 1969 we extracted 2,551 eggs
from an unmated female imago; 38 nymphs hatched. Although the
percentage of unfertilized eggs that hatched was very low compared
to fertilized eggs (Table 1), the data indicate that parthenogenetic
development can occur in B. rogersi. Further, the fact that eggs ex-
tracted from subimagos hatched suggests that eggs are mature in the
subimaginal stage.
The ratio of males to females was more or less equal. Combined
results for two years showed a 0.81:1.00 ratio (49 males, 59 females)
for adults reared in the laboratory. Of 408 nymphs collected from the
two localities, 194 were males and 208 were females, a 0.90:1.00 ratio.
B. rogersi can be parthenogenetic, although males and females are more
or less equal in proportion.

EGG NUMBER
Table 12 gives egg counts made on 19 females of B. rogersi. The
average number of eggs per individual was 2,168. In 1969 the largest
number was 2,650 and the smallest was 1,500. As individuals emerging
late in the season are usually smaller than those emerging earlier, it was


1974







BULLETIN FLORIDA STATE MUSEUM


expected that they would produce relatively fewer eggs. Table 12 shows
this to be generally true.

SEASONAL DISTRIBUTION
The seasonal distribution of images as determined from emerging
subimagos extended from March through early July. Tables 3 and 4
show that twelfth instar nymphs first appeared in February, increasing
in March. Emergence began in March. The earliest emergence record
in the field was 13 March 1969 and the latest 8 July 1969, but, we re-
visited the stream the following week and found two more nymphal
exuviae on stumps. The exact emergence date of these specimens cannot
be ascertained because the exuviae were decolorized and disintegrated.
Newly cast nymphal exuviae retain the color of the last nympal instar
for a day, and the linings of the rupture are whitish in color. We made
several more attempts to collect images, nymphal exuviae, and nymphs
in the following weeks, but found none. In the laboratory, the earliest
emergence was 10 March 1968 and the last 30 June 1968. In 1969
emergence extended from 9 March to 26 June. One twelfth instar nymph
however remained alive until July but did not emerge.
The peak of emergence occurred in April both years (Tables 3 and
4). Laboratory emergence records also showed an April peak. Emer-
gence did not extend past the middle of summer, reflecting a strictly
seasonal distribution permitting only one generation a year.

SUMMARY
We studied the life history, ecology, and seasonal distribution of
Baetisca rogersi in the laboratory and in Rocky Comfort and Bear
Creeks, Gadsden County, Florida, 1967-1969. In the laboratory fertilized
eggs began to hatch in 20-31 days, averaging 23.8 days, and unfertilized
eggs averaged 26.6 days. We found nymphs in the study areas from
September through June and assume that eggs remained dormant during
the summer. We raised twelve nymphal instars in the laboratory, a
nymph taking approximately four months to mature. In the field, early
instar nymphs lived on a substratum with water moss, Leptodictyum
riparium, and filamentous algae, Spirogyra sp. Mature nymphs at Rocky
Comfort Creek lived in shallow areas of gravel and sand. In Bear
Creek, a sand bottom stream, the nymphs lived on submerged logs or in
the sand. Twelfth instar nymphs migrated to quiet sections of the
stream prior to emergence, probably searching for above-water objects
where the nymphs could emerge.
The nymphs swim with vigorous and rapid undulations of the last


Vol. 17, No. 3








PESCADOR AND PETERS: BAETISCA ROGERSI


three abdominal segments including the caudal filaments, using the gills
only for respiration. The lateral spines of the thoracic notal shield bal-
ance and maintain the dorsoventral position of the nymphs. The nymphs
feed on detritus, diatoms, and fragments of filamentous algae; they feed
at night. In the field, nymphal growth slowed in December and January
and resumed in the latter part of January.
Emergence was strictly seasonal, permitting only one generation per
year. Subimagos emerged from March through early July with the peak
emergence in April. They emerged in the field between 8:30 AM and
2:30 PM with a peak between 8:30 AM and 10:30 AM. In the laboratory
they emerged from 10:00 AM to 8:30 PM (peak emergence from 12:00
PM to 3:00 PM). The duration of the subimaginal stage ranged from
12 to 30 hours, averaging 20 to 24 hours. The images lived an average
of 21 hr 8 min in the laboratory. Female images produced 1,500 to
2,727 eggs averaging 2,168 eggs.

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(Ephemeroptera: Baetidae). Oecologia (Berlin), 9:47-51.
Froehlich, C. G. 1969. Caenis cuniana sp. n., a parthenogenetic mayfly. Beitrige
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1974







BULLETIN FLORIDA STATE MUSEUM


Gledhill, T. 1959. The life history of Ameletus inopinatus (Siphlonuridae, Ephemer-
opertera). Hydrobiologia, 14:85-89.
Harker, J. E. 1952. A study of the life cycles and growth-rates of four species of
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1974 PESCADOR AND PETERS: BAETISCA ROGERSI 209

Traver, J. R. 1931. The ephemerid genus Baetisca. J. N. Y. Entomol. Soc., 39:
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S-70-. Y d


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