Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; 234
Title: The two-spotted mite (Tetranychus telarius L.) on Asparagus plumosus
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Permanent Link: http://ufdc.ufl.edu/UF00026417/00001
 Material Information
Title: The two-spotted mite (Tetranychus telarius L.) on Asparagus plumosus
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 20 p. : ill., chart ; 23 cm.
Language: English
Creator: Wilson, J. W ( John Wallace ), 1902-
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1931
 Subjects
Subject: Tetranychus telarius   ( lcsh )
Asparagus -- Diseases and pests -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Bibliography: p. 20.
Statement of Responsibility: by J.W. Wilson.
General Note: Cover title.
 Record Information
Bibliographic ID: UF00026417
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000924084
oclc - 18204217
notis - AEN4688

Full Text





HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida











UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
Wilmon Newell, Director








THE TWO-SPOTTED MITE


(TETRANYCHUS TELARIUS L)

ON ASPARAGUS PLUMOSUS

By J. W. WILSON


CONTENTS


Distribution
Host plants
Injury
Seasonal history
Description and habits
Dispersion .
Climatic control
Natural enemies
Control measures
Summary .
Literature cited .....


TECHNICAL BULLETIN



Bulletins will be sent free upon application to the
Agricultural Experiment Station
GAINESVILLE, FLORIDA


Bulletin 234


June, 1931


PAGE
3
4
5
5

13
..... 14
15
15
19
.... 20








BOARD OF CONTROL


P. K. YONGE. Chairman, Pensacola
A. H. BLENDING, Bartow
W. B. DAVIS, Perry


PAYMER F. MAGUIRE, Orlando
FRANK J. WIDEMAN, West Palm Beach
J. T. DIAMOND, Secretary, Tallahassee


STATION EXECUTIVE STAFF

JOHN J. TIGERT, M.A., LL.D., President 1t. M. FULGHUM, B.S.A., Asst. Editor
WILMON NEWELL, D.Sc., Director IDA KEELING CRESAP. Librarian
H. HAROLD HUME, M.S., Asst. Dir., Re- RUBY NEWHALL, Secretary
search K. H. GRAHAM, Business Manager
S. T. FLEMING, A.B., Asst. Dir., Admin. RACHEL McQUARRIE, Accountant
J. FRANCIS COOPER, M.S.A., Editor

MAIN STATION-DEPARTMENTS AND INVESTIGATORS


AGRONOMY
W. E. STOKES, M.S., Agronomist
W. A. LEUKEL, Ph.D., Associate
G. E. RITCHEY, M.S.A., Assistant*
FRED H. HULL, M.S., Assistant
J. D. WARNER, M.S., Assistant
JOHN P. CAMP, M.S.A., Assistant
ANIMAL HUSBANDRY
A. L. SHEALY, D.V.M., Veterinarian in
Charge
E. F. THOMAS, D.V.M., Asst. Veterinarian
R. B. BECKER, Ph.D., Associate in Dairy
Husbandry.
W. M. NEAL, Ph.D., Assistant in Animal
Nutrition
C. R. DAWSON, B.S.A., Assistant Dairy
Investigations
CHEMISTRY
R. W. RUPRECHT, Ph.D., Chemist
R. M. BARNETTE, Ph.D., Associate
C. E. BELL, M.S., Assistant
J. M. COLEMAN, B.S., Assistant
H. W. WINSOR, B.S.A., Assistant
H. W. JONES, B.S., Assistant
COTTON INVESTIGATIONS
E F. GROSSMAN, M.A., Assistant
P. W. CALHOUN, B.S., Assistant


ECONOMICS, AGRICULTURAL
C. V. NOBLE, Ph.D., Agricultural Economist
BRUCE McKINLEY, A.B., B.S.A., Associate
M. A. BROOKER, Ph.D., Assistant
ECONOMICS, HOME
OUIDA DAVIS ABBOTT, Ph.D., Head
L. W. GADDUM, Ph.D., Biochemist
C. F. AHMANN, Ph.D., Physiologist
ENTOMOLOGY
J. R. WATSON, A. M., Entomologist
A. N. TISSOT, M.S., Assistant
H. E. BRATLEY, M.S.A., Assistant
L. W. ZIEGLER, B.S., Assistant
HORTICULTURE
A. F. CAMP, Ph.D., Horticulturist
HAROLD MOWRY, B.S.A., Associate
M. R. ENSIGN, M.S., Assistant
A. L. STAHL, Ph.D., Assistant
G. H. BLACKMON, M.S.A., Pecan Culturist
C B. VAN CLEEF, M.S.A., Greenhouse
Foreman
PLANT PATHOLOGY
W. B. T1SDALE, Ph.D., Plant Pathologist
G. F. WEBER, Ph.D., Associate
A H EDDINS, Ph.D., Assistant
K. W. LOUCKS, M.S., Assistant
ERDMAN WEST, M.S., Mycologist


BRANCH STATION AND FIELD WORKERS
L. O. GRATZ, Ph.D., Asso. Plant Pathologist in charge, Tobacco Exp. Sta. (Quincy)
R. R. KINCAID, M.S., Assistant Plant Pathologist (Quincy)
W. A. CARVER, Ph.D., Assistant, Cotton Investigations (Quincy)
RAYMOND M. CROWN, B.S.A., Field Asst., Cotton Investigations (Quincy)
JESSE REEVES, Farm Superintendent, Tobacco Experiment Station (Quincy)
J. H. JEFFERIES, Superintendent, Citrus Experiment Station (Lake Alfred)
GEO. D. RUEHLE, Ph.D., Assistant Plant Pathologist (Lake Alfred)
W. A. KUNTZ, A.M., Assistant Plant Pathologist (Lake Alfred)
B. R. FUDGE, Ph.D., Assistant Chemist (Lake Alfred)
W. L. THOMPSON, B.S., Assistant Entomologist (Lake Alfred)
R. V. ALLISON, Ph.D., Soils Specialist in charge Everglades Experiment Sta. (Belle Glade)
R. W. KIDDER, B.S., Foreman, Everglades Experiment Station (Belle Glade)
R. N. LOBDELL, M.S., Assistant Entomologist (Belle Glade)
F. D. STEVENS, B.S., Sugarcane Agronomist (Belle Glade)
H. H. WEDGEWORTH, M.S., Associate Plant Pathologist (Belle Glade)
B. A. BOURNE, M.S., Associate Plant Physiologist (Belle Glade)
J. R. NELLER, Ph.D., Associate Biochemist (Belle Glade)
A. DAANE, Ph.D., Associate Agronomist (Belle Glade)
FRED YOUNT, Office Assistant (Belle Glade)
M. R. BEDSOLE, M.S.A., Assistant Chemist (Belle Glade)
A. N. BROOKS, Ph.D., Associate Plant Pathologist (Plant City)
R. E. NOLEN, M.S.A., Field Assistant in Plant Pathology (Plant City)
A. S. RHOADS, Ph.D., Associate Plant Pathologist (Cocoa)
C. M. TUCKER, Ph.D., Associate Plant Pathologist (Hastings)
H. S. WOLFE, Ph.D., Associate Horticulturist (Homestead)
L. R. TOY, B.S.A., Assistant Horticulturist (Homestead)
STACY O. HAWKINS, M.A., Field Assistant in Plant Pathology (Homestead)
D. G. A. KELBERT, Field Assistant in Plant Pathology (Bradenton)
FRED W. WALKER, Assistant Entomologist (Monticello)
D. A. SANDERS, D.V.M., Associate Veterinarian (West Palm Beach)
M. N. WALKER, Ph.D., Associate Plant Pathologist (Leesburg)
W. B. SHIPPY, Ph.D., Assistant Plant Pathologist (Leesburg)
C. C. GOFF, M.S., Assistant Entomologist (Leesburg)
J. W. WILSON, Ph.D., Assistant Entomologist (Pierson)

*In cooperation with U. S. Department of Agriculture.






THE TWO-SPOTTED MITE

(TETRANYCHUS TELA RIUS L,)

ON ASPARAGUS PLUMOSUS

By J. W. WILSON
The two-spotted mite (Tetranychus telarits) belongs to the
family of spinning mites (TETRANYCHIDAE) and is known
in many sections of the country as the "red spider." Another
species of mite, salmon pink in color, and recently described by
McGregor (4)' as Divarinychus floridensis is known among
Florida growers of Asparagus plumosus as the red spider, and
thus Tetranychus telarius is commonly called the two-spotted
mite because of the dark spot at each side of the cephalothorax,
or the California mite, because it is supposed to have been intro-
duced in shipments of Asparagus plumosus seed from Cali-
fornia.
This species of mite was first reported on Asparagus plumosus
from Pierson about the year 1925, and when it first appeared
the growers attempted to control it with sulfur dust or liquid
lime-sulfur, as had been their custom with Dirarinychus flori-
densis. During the spring of 1929 Mr. W. W. Others and Mr.
C. B. Keck of the U.S.D.A. Bureau of Entomology at Orlando,
Florida, devoted some time to the study of this pest, but due to
the urgency of other work they were unable to continue their
studies. In January, 1930, the Florida Experiment Station estab-
lished a field laboratory at Pierson for the study of this mite.

DISTRIBUTION
The two-spotted mite is one of our earliest pests introduced
from Europe. It was first reported on cultivated crops from
New England and the Northeastern States. In 1855 (2) Glover
reported some injury to cotton but it was not until 1903 that
the two-spotted mite was reported as severely damaging cotton
in South Carolina and Georgia. This mite is now found from
Maine to Florida and as far west as Texas. It is generally dis-
tributed in New England, New York, Illinois, the southern part
of Wisconsin and Michigan, western Colorado, the Willamette
Valley of Oregon and the interior region and southern part of
California. In Florida, other workers have reported the mite
'Figures in parentheses (italic) refer to "Literature Cited" in the back
of this bulletin.







Florida Agricultural Experiment Station


from Eustis, Galloway, Key Largo, Miami, Orlando, Punta
Gorda, St. Nicholas, and St. Petersburg. It has been found at-
tacking Asparagus plumosus in most of the slat houses of Vol-
usia County, three slat houses at Yalaha, and most of the fern-
eries at Groveland. The original infestation at both Yalaha
and Groveland occurred in ferneries set with plants purchased
at Pierson. Thus it seems that the mites have been carried on
infested plants from Pierson to these other two centers. Recent-
ly an infestation at Leesburg has been discovered.

HOST PLANTS

McGregor and McDonough (1917) (5), working in South
Carolina, listed 183 species of plants upon which they found the
two-spotted mite feeding. This list included weeds, ornamentals,
and garden and field crops. This mite is very commonly found
in greenhouses feeding on a large number of plants growing
there. In a greenhouse at Pierson this mite was very common
on Crotons. Workers in other sections of the country report
that the favorite host plants are violet and blackberry.
In the slat houses the mites attack almost all of the weeds
growing there as well as Asparagus plumosus. In fact, night-
shade (Solan mm gracile) and cudweed (Gnaphalium obtusi-
folium) are preferred to Asparagus by the mites. The mites
were found feeding upon the following list of weeds in the
fernery:


PLANT COMMON
Adopogon dandelion* Dwarf dandelion
Aster sp. Aster
Berlandiera subacaulis
Carphephorus corymbosus
Chamaesyce buxifolia
Chenopodium ambrosioides Mexican tea
Crotalaria purshii
Crotalaria rotundifolia
Datura stramonium Jimson weed
Eryngiumn aromaticum Snakeroot
Eupatorium compositifolium Dog fennell
Geranium carolinianum Wild geranium
Gnaphalium obtusifolium Cudweed
Heterotheca subaxillaris
Lycopersicon sp. Wild tomato
Phytolacca americana Pokeweed
Pycnothymus rigidus
Rumex acetosella Horse sorrell
Sida rhombifolia Teaweed
Solanum gracile Nightshade
Thyransanthema semiiflosculare
*The writer is indebted to Mr. Erdman West for the
the above list of plants.


NAME
n


identification of






Bulletin 234, Two-Spotted Mite on Asparagus Plumosus 5

INJURY

The part of the Asparagus plant most attractive to the mites
is the tender, rapidly growing, new shoots. In cool or cloudy
weather the adult mites are usually found beneath the bracts on
these shoots, and it is beneath these bracts that first signs of
injury are noticed. A small white spot develops around each
feeding puncture and when these punctures become numerous
the shoot assumes a mottled gray appearance. Spots beneath
the bracts gradually turn brown as a result of large numbers of
feeding punctures. Continued removal of the plant juices by
the mites prevents the normal development of the spray, which
remains dwarfed in size and yellowish in color. Sprays in this
condition have no commercial value. Very heavy infestations
of the mites cause the whole plant to turn brown and it is fre-
quently covered with a very fine webbing. The two-spotted mite
usually confines its activity to the young developing shoots and
it is only in cases of very heavy infestation that it is found on
shoots which have developed leaflets.

SEASONAL HISTORY

Several writers in both Europe and America have shown that
the two-spotted mite hibernates in colder climates and passes
the winter in the adult stage. Von Hanstein (1902) (3) found
this mite in large numbers in the bark, and about the crown
roots of trees which had been severely infested. Weldon (1909)
(8) working in Colorado found that the mites begin their down-
ward migration toward the end of July. He states that large
numbers of mites were found in the soil at the crown of trees
upon which they had been feeding. Worsham (1910) (9) first
recognized the fact that in the Southeast the mites remain active
and continue to propagate slowly during the winter. McGregor
and McDonough (1917) (5), working at Batesburg, S. C., have
shown that the mites migrate from the cotton fields to a succes-
sion of fall and winter host plants and back to the cotton again
in spring.
It is commonly believed in the Pierson area that the mites
hibernate in the bark of posts and cracks of the slat houses or
at the roots of the plants. Repeated examinations of the bark
and roots of the plants have not revealed the mites. Trash and
material from the surface of the soil was collected in the fall







Florida Agricultural Experiment Station


and placed in a Berlese funnel but no mites were obtained. How-
ever, the mites have been observed in small numbers in the slat
houses during all months of the year and were bred in the open
insectary on Asparagus plants during the winter months.
Feb. MIr. Apel M4y JAue Jly Au I.s. oet. t or Dec Jan.



S\ 17

I I
7I i ti


Pr \ t .o I al

7 1 4. I i
: tI I 111
SI I











seu males lid e o the of u The m it
,, I I I

us l f F


VA \ / / >
v \' V N j

Fig. 1.-Simultaneous curves showing the relationship between the prevail-
ing temperature and the length of time required for eggs of the two-
spotted mite to hatch. Incubation period in days represented by the
solid line, and the mean temperature by the broken line.

These females laid eggs on the 3rd of January. The mites
are most abundant during the warm, dry weather of spring,
usually from February until June. The work was begun at
Pierson on the 1st of January, 1930, and a few adult females
were collected on the 2nd of January. When the summer rains
begin in June the mites gradually decrease in numbers until
the following spring. By the 22nd of January, 1930, the mites
had become abundant enough to begin experimental spray tests
and by the middle of February they were abundant enough to
do serious damage in many of the slat houses. The month of
March was unusually wet, the average rainfall for the State be-
ing 7.37 inches, 4.31 inches above the normal. This excessive







Bulletin 234, T'wo-Spotted Mite on Asparagus Plumosus 7

amount of rain held the mites in check, but they again became
abundant during April and May. The summer rains began on
the 2nd of June and the mites gradually became less abundant.
Mites of all stages were observed on occasional visit to various
slat houses during the remaining months of the year, but very
few mites were found in November and December. The spring
of 1931 has been exceptionally cool and wet and as a result the
mites have not become abundant enough to do damage except in
two slat houses up to the present time (April 20).

DESCRIPTION AND HABITS

THE EGG
The eggs are small and spherical in shape, and are not readily
visible to the naked eye. Although very minute in size they are
relatively large when compared with the size of the adult female
mite. A series of eggs measured .108 mm. in diameter. The
eggs are deposited singly and usually beneath
the bracts on the young Asparagus shoots, 3- "
but where the infestation is heavy the eggs '
are found on the side of the stems and in the
webbing spun beneath the bracts. The eggs .
when first laid are clear in color and gradu-
ally turn a light straw color. During the lat- Fig. 2.Eg of
Fig. 2. Egg of
ter part of the incubation period the red eye- Tetranychus te-
irriuts L. x200.
spot appears. riina. x200
Number of Eggs Laid.-The number of
eggs laid by a single female varies very widely, and is influenced
largely by temperature and food conditions. Table I gives the
average number of eggs laid by females of 11 successive genera-
tions from February to July. The largest number of eggs depos-
ited by a single female was 123, and the largest number of eggs
laid during a single day was 14. which occurred twice. Nine, 10,
and 12 eggs a day are frequently laid during April and May. From
Table I, it is seen that a single female will produce on the aver-
age 70 eggs at the rate of 3 to 7 a day. It will be noticed also that
the average number of eggs per female per day gradually in-
creases during the spring and summer months, while the length
of the oviposition period decreases.
Incubation Period.- The length of the incubation period is
very closely related to the prevailing temperatures. (Fig. 1.)
During the winter months when the mean daily temperature








Florida Agricultural Experiment Station


ranges from 500 to 550 F., eggs required as long as 15 days to
hatch; in one case eggs deposited on the 29th of January re-
quired 17 days to hatch. From May to the 15th of October the
average length of the incubation period was 3.59 days. One
brood deposited on the 10th of July hatched in 2 days. The
average length of the incubation period for the entire season
was 5.84 days, based on 98 broods.
TABLE I.-RECORD OF FEMALES FOR 11 SUCCESSIVE GENERATIONS.


No. i
gen. |
Number
I females I

1 11

2 5

3 4
4 4
5 8
6 6

7 5
8 6

9 7
10 5
11 2


Date
first
egg
laid

2/11

2/28
3/21
4/ 6

4/19

5/ 4
5/14
5/23

6/ 2

6/14
6/24


SAverage I
Spre-ovi- I Average
Position [ number
period, I eggs per
days | female

2.27 70.36

2.20 76.40
2.50 78.75
1.00 75.80

1.37 65.12
1.33 78.51

1.00 68.20
1.16 69.66

1.42 41.00
1.00 58.80
1.00 98.00


SAverage I
Length Average
[ oviposi- number Average
tion eggs per| length
period, I day per [of life for
days female females

20.81 3.38 22.72
26.40 2.89 30.00
18.50 4.23 20.75
16.20 4.68 17.20
16.00 4.07 17.62
14.00 5.61 16.66
11.60 5.88 12.60
13.83 5.03 15.00
7.14 5.74 9.28

9.00 6.53 12.50
13.00 7.54 14.00


LARVAL STAGE
Description.-The newly hatched larva is colorless, except for
the bright carmine eye-spot, and has only six legs. At the time
of hatching the larva is round and the same size as the egg. It
begins feeding immediately and gradually turns a light green in
color and a small black spot appears at each side of the body
just back of the eye-spot. The following dimensions were ob-
tained from a series of larvae: Length .149 mm., width .116 mm.
When the larva attains its growth it enters a resting stage.
The mouth parts are thrust into the tissue of the plant, the
front two pairs of legs are extended parallel to each other and in
a forward direction while the hind pair of legs are extended
along the sides of the body. During the months of December,
January, and February this resting stage will last for some time







Bulletin 234, Two-Spotted Mite on Asparagus Plumosus 9

if the temperatures are low, but dur-
ing the warmer months this resting
period lasts only a few hours. The
average duration of the resting stage
of 8 larvae observed during January
and February was 2.25 days.
Length of Larval Instar.-For 76
colonies of larvae the average time
required for the development of this
stage was 2.64 days for the whole
year. From January to the 15th of
April the larvae developed in 4.25
days, from the 15th of April to the
15th of May this instar required 2.20 \
days, and from the 15th of May to
the 1st of September 1.89 days were
required to complete this instar.
Fig. 3.-Larva of Tetrany-
FIRST NYMPHAL STAGE c h u s telarius L. x200.
(Original.)
In addition to being larger, this (Origi
stage differs from the larval stage in that it has four pairs of
legs instead of three pairs. The dark spots at the sides of the
body are slightly larger and the bristles on the body are longer.
Measurements of the first nymphs averaged: length .217 mm.,
width .141 mm.
The first stage nymphs are somewhat more active than the
larvae but their habits are similar. The nymphs begin feeding
soon after the molting process is completed. Like the larvae,
the first stage nymphs pass through a resting period, or pre-
molting period, which lasts for an average of 2.23 days during
the winter months and for only a few hours during the more
active period.
The length of time required for the completion of this instar
for the 76 colonies reared was 2.12 days. As with the larvae,
this instar lasted much longer during the colder months. It
required 3.25 days from January to the 15th of April; 1.80 days
from the 15th of April to the 15th of May; and 1.61 days from
the 15th of May to the 1st of September.

SECOND NYMPHAL STAGE
The second nymphal stage differs from the first only in that
in the case of females the body of the second nymphal stage is







Florida Agricultural Experiment Station


larger and longer. The average
length of females of this stage
was .313 mm. and the average
width was .194 mm. McGregor,
working in South Carolina, re-
ports that only females pass
through the second nymphal
/ stage, but all the males reared
during the course of this study
Smolted a third time. In the
case of the males, however,
S.............-- the duration of this stage av-
Ieraged one day shorter than
for the females, so that the
adult males always appeared
S before the females. In several
cases the males were observed
assisting the females to shed
the last nymphal skin.
The average length of time
Fig. 4.- First nymphal stage of required for the second nym-
Tetraiychus telarius L. x200.
(Original.) phal stage was 2.60 days. One
colony which hatched on the
16th of February required 13 days for the completion of this
stage, but even during the cooler months this stage rarely re-
quired more than 6 days, while in the summer months the stage
is frequently completed in 1 day. This instar also passes through
a short resting period before the last nymphal skin is shed.

ADULTS

The adult female is broader and longer than the male, meas-
uring .423 mm. in length, and .251 mm. in width; while the male
measures .249 mm. in length and .135 mm. in width. The fe-
males vary considerably in color, ranging from a light green to
black. Occasionally light yellow and red individuals are observed,
but most of the individuals are green in color with a black spot
at each side of the body. The variations in color in the male are
very slight. Most of the individuals are light green in color
with small black spots at the side of the body and a prominent
red eye-spot.






Bulletin 274, Two-Spotted Mite on Asparagu~s Plumouss 11

As has already
been stated the
males have been ob-
served assisting fe-
males from the last
nymphal skin and
in these cases copu-
lation took place
immediately follow-
ing t h e female's
complete freedom
from the nymphal
skin. After mating,
the females begin
feeding almost im-
mediately and pass
through a short
pre-oviposition pe-
riod which was \ /
found to be 1.48 /.
days for 64 females.
This pre-oviposition
period was not ob-
served to be length-
ened in the cases of
L n f e 1r t i 1 i z e d
unfertilized //
females. The aver-
age egg-laying pe-
riod for the 64 fe-
males extended
through a period of Fig. .--Adult male two-spotted mite, Tetrany-
15.13 da y s. The chus telrius L. x200. (Original.)
longest oviposition period for a single female was 44 days, the
first egg being deposited on the 25th of February.

NUMBER OF GENERATIONS
Early in January, when the work was first begun at Pierson,
female mites were collected in the slat houses, transferred to
short sections of tender Asparagus stems, which were placed in
stoppers made of absorbent cotton and inserted in shell vials cor-
taining water. Fresh stems were supplied each day and thus the








Florida Agricultural Experiment Station


\ 1


Fig. 6.-Adult female two-spotted mite, Tetranychus telarhis L.
x184. (Original.)


.;.~.S
..:~
;:

.:
:'
.:: :i
`:: :

..:
::':


:i::





: ~i~i






Bulletin 234, Two-Spotted Mite on Asparagus Plumosus 13

daily records were obtained. These stems with the mites were
kept in the screened insectary. By this means 11 successive gen-
erations were reared up to the 24th of June. Although it was
impossible to continue rearing successive generations, many
broods were reared during the remaining months of the year and
from these data it was found that the average time required for
the completion of a generation was 14.64 days. Since the mites
breed in this locality during the entire year there should be ap-
proximately 24 generations a year. As is to be expected from the
data already presented, generations developing during the win-
ter months required a much longer time than those developing
during the summer months.
PARTHENOGENESIS
Several workers have reported that the unfertilized females
will lay eggs and that these eggs produce males. Perkins (1897)
(6) states that unfertilized females readily lay eggs and that
these eggs produce only males. Ewing (1914) (1) working in
Oregon, reared the progeny of 3 virgin females, and all of them
were males. It has also been shown that males developing from
unfertilized eggs are completely potent and when mated with vir-
gin females the two sexes begin to develop in the usual propor-
tion.
Parthenogenesis thus becomes an important factor in the bi-
ology of the mites. In cases where unfertilized females become
established in a new locality, their first offspring will be males.
When these males mature they will mate with the female and
individuals of both sexes will begin to appear in the usual pro-
portions.
DISPERSION

Workers in other parts of the country have shown that sev-
eral factors are responsible for the distribution of the mites.
Stabler (7), and McGregor and McDonough (5), by suspending
sticky flypaper at various heights and distances from infested
areas, have shown that the wind is an important factor in dis-
tribution. Another important means of spreading is that of
travel from plant to plant. In the slat houses at Pierson it seems
that the most important means of dispersion is by the clothing
of workmen. The mites are brushed from the plants and may be
carried to some other part of the slat house or other slat houses
and brushed off there. In the cases where mites have become






Florida Agricultural Experiment Station


established in other sections of the State, dispersion can be
traced to the transportation of infested seedling plants, except-
ing the most recent infestation at Leesburg. McGregor and Mc-
Donough also state that in cotton fields the mites are carried
from one part of the field to another by heavy washing rains.

CLIMATIC CONTROL

It has been generally observed in Florida and other sections
of the country that the two-spotted mite is most abundant dur-
ing seasons of dry, hot weather. Very few mites were present
in slat houses during January, but during February, 1930, there
was a period of two weeks of dry, hot weather when the tem-
perature reached 85 F. and above. During this period, the mites
developed rapidly and became quite abundant. During March
the infestation was checked considerably as the rainfall was
4.31 inches above normal and the average temperature for the
state was 3.70 F. below normal. The infestation rapidly in-
creased during April and reached its maximum in May. The
summer rains began on the 2nd of June and thereafter the mites
were less abundant. During the months of January, February,
and March of 1931 rains and low temperatures prevailed, and
the mites did not become abundant enough to damage Aspara-
gus plumosus until the second week in April. Heavy rains on
the 6th of March reduced the number of mites on a check plot
56.6 percent, and on the 28th of March reduced the number of
mites 34.57 percent, and another rain on the 26th of April re-
duced the number of mites 38.98 percent.
Several slat houses in this locality are equipped with irriga-
tion systems. The growers irrigate their slat houses regularly
for about an hour on alternate days during the dry, warm pe-
riods of spring. Small infestations of mites have been observed
in these ferneries, but they disappeared soon after the water
was turned on. The growers state that they have not been seri-
ously troubled with mites since the installation of the irriga-
tion systems. The successful use of this control method depends
to a large extent upon an early application of water before the
mites become firmly established. Growers using the irrigation
system should watch the slat house closely and start irrigating
as soon as the mites begin to appear during warm, dry weather.
Other growers have successfully controlled the mites with
less frequent applications of water by using a hose and thor-






Bulletin 234, Two-Spotted Mite on Asparagus Plumosus 15

oughly wetting the plants. Where the infestation has become
heavy this method gives quicker results than the first method.
In one slat house where the hose method was used, water was
applied every three days and almost complete control was ob-
tained in three weeks.

NATURAL ENEMIES

Investigators in other parts of the country report that the
mites are destroyed by a large number of predators. McGregor
and McDonough list five species of mites and 26 species of in-
sects which feed upon the two-spotted mite in South Carolina.
This list includes the ladybird beetles, Stethorus punctum and
Stethorus utilis, the aphis lion Ch ., **'. rufilabris, and a preda-
tory thrips, Scolothrips se.'maculatus.
During the course of the investigations at Pierson, mite colo-
nies were closely watched for predators. Only two species have
been observed up to the present. One of these, the mite Seius
quadripilis, feeds upon the eggs of the two-spotted mite. It was
not found to be very abundant in this locality and did not cause
a marked reduction in the number of mites present. The other
was Scolothrips se.,nmaculatus. Only a few specimens were found
on the 26th of May, 1930. From these observations it is appar-
ent that insect enemies do not play a large part in the control of
the two-spotted mite at the present time.

CONTROL MEASURES

It has already been pointed out that 21 species of weed host
plants for the two-spotted mite grow in the slat houses, and
that the mite prefers the nightshade (Solanumn gracile), cud-
weed (Gnaphalium obtusifoloiu), and tea weed (Sida rhombi-
folia) to Asparagus. The mites gather on the undersides of the
leaves of these plants and it is very difficult to reach them with
an insecticide. Where weeds were allowed to remain in the slat
house they have been observed to act as sources for reinfesting
the fernery after spray materials had been applied to the fern
plants. The removal of all weeds from a fernery is a very im-
portant point in the program for the control of the mites. It is
also important that a strip of land six to eight feet wide be kept
clear of all vegetation, as this materially lessens the chances of
reinfestation from plants outside the fernery.






Florida Agricultural Experiment Station


SPRAYS AND DUSTS
Liquid spray materials used in experiments to control the two-
spotted mite included nicotine compounds, a derris compound,
pyrethrum, soap solutions, and oil emulsions. A large number of
tests were made in which these materials were used. In some
cases rain fell a few hours after the spray material had been
applied and in these cases it was difficult to determine the ef-
fects of the spray material. In the case of the soap solutions
and the oil emulsions, plots were sprayed two or three times at
seven-day intervals to determine the effect of repeated sprays
upon the plants. In all cases records were kept of the time at
which the application was made and the temperature.
Sulphur Dusts.-The growers in this locality have repeatedly
found that flowers of sulphur dusted upon plants was not ef-
fective in controlling the mites. During May, when the tem-
peratures ranged from 80 to 950 F., sulphur dusts were ap-
plied with no result. On the 1st of May an application of nine
parts of flowers of sulphur and one part sodium fluoride was
made. This dust severely burned the ferns and very few mites
were killed. A mixture of 20 percent dry lime sulphur with 80
percent flowers of sulphur had no effect upon the mites. Two
commercial brands of colloidal sulphur were used without re-
ducing the mite population. All of these materials were tested
during May when the temperature was above 850 F., and when
the latter two materials were applied the thermometer regis-
tered a temperature of 930 F.
Nicotine Compounds.-A sulfonated oil derivative was used
as a spreader in a number of tests with nicotine sulfate and 50
percent free nicotine. Even in tests where the sulfonated oil
derivative was diluted at 1-200 slight burning resulted when
the temperatures were above 800. In other sprays potassium
oleate was used as a spreader, but with the concentration of the
50 percent free nicotine as high as 1-800, only 66 percent of the
mites were killed. Thus the nicotine sprays were considered in-
effective as a control for the two-spotted mite.
Pyrethrum Compounds.-Sprays containing pyrethrum were
likewise found to be of very little value in controlling the mites.
A kill of 73.68 percent was obtained with a well known commer-
cial brand, 1-60. A combination of pyrethrum dissolved in the
sulfonated oil derivative mentioned above at 1-100 gave a con-
trol of 81.58 percent, but here again burning resulted from the






Bulletin 234, Tiwo-Spotted Mite on Asparagus Plumosus 17

use of the sulfonated-oil derivative in the spray material. Other
pyrethrum preparations containing no soap were used, soap be-
ing added when the spray material was prepared. A 65.54 per-
cent kill was the best obtained with a concentration of 1-100.
Derris Compounds.-The sulfonated oil derivative was used
as a spreader with a compound of derris, but after a few days'
time the plants showed severe burning. Sprays in which the
derris compound, 1-400, and a white oil emulsion, 1-400, were
used gave good controls and no burning effects. At a dilution of
1-600 for the derris compound 85 percent of the mites were
killed.
Soap Solutions.-During the early spring months when there
were rains at frequent intervals and the temperatures did not
go above 75 F., solutions of soap gave very good results. Four
commercial soaps, including one of pine oil used at the rate of
eight pounds of soap to 100 gallons of water did not injure the
foliage. In cases where the soap was applied after the 1st of
April when rains came at longer intervals and the temperatures
were higher it was only the second spraying with soap that in-
jured the plants. During dry, hot weather, soap sprays must be
used very cautiously. A solution of fish-oil soap has been used,
but the odor imparted to the ferns is very objectionable and
reduces the commercial value of the ferns.
White Oil Emulsions.-The white oil emulsions used in experi-
ments to control the mites included three commercial brands.
These emulsions used at the rate of one gallon of the emulsion
to 100 gallons of water gave a control of 94 to 98 percent. Dur-
ing the early spring months when the mites were less active,
complete control with these sprays was obtained, but during
April and May a 98 percent control was the highest obtained.
The plots upon which these oil emulsions were used were sprayed
two and three times at seven-day intervals. After the third ap-
plication, a complete control was obtained and no damage to the
ferns resulted. At the dilution of 1-100 one commercial red oil
emulsion gave a poor control. Another gave a complete control
but in May, with the higher temperatures, injury to the plants
resulted from the use of this spray. A single plot was sprayed
with kerosene oil emulsion. The stock solution was made up by
the standard formula and diluted at the rate of 1 to 100. This
concentration of the oil did not give a good control and the ferns
sprayed with this material retained an objectionable odor for






Florida Agricultural Experiment Station


some time. These tests showed that white oil emulsions are
safe and effective oil emulsions to be used against the mites.
Miscible Oil.-A commercial miscible oil at 1-100 and a sulfur
compound at 1-200 in combination gave complete control of the
mites, but severe burning resulted from the use of these mate-
rials. The miscible oil alone at 1-100 killed 76.85 percent of the
mites. At 1-75 it gave complete control, but the effect upon the
plant was not determined because of rains which fell soon after
the application of this spray.

METHODS OF APPLYING THE SPRAY
As has already been shown, the eggs of the mite will hatch in
three to five days during the warmer months and from six to
eight days are required for the mites' development. Hence, if
the spray material is applied at an interval of seven days. suf-
ficient time will have elapsed for the eggs to hatch and not
enough time for another generation to start laying eggs. The
object of the first spray then is to destroy the adult mites and
stop egg laying, and a second application seven days later will
destroy the immature mites which have hatched out. A cnm-
plete control with two applications of the spray material pre-
supposes a thorough wetting of the plants and all mites on the
plants.
Since the two-spotted mite has sucking mouth parts, each in-
dividual mite must be wet with the spray material to obtain a
control. Spraying experiments have indicated that 500 to 600
gallons per acre of material will be required to completely wet all
parts of the plants above ground. In applying the spray the
nozzle of the spray rod should be directed upward so thai; the
spray material will be forced beneath the bracts where many
of the mites are found. Best results will be obtained where a
pressure of 200 pounds is maintained. Especial care must be
exercised to wet the long tender shoots thoroughly, as it is on
them that large numbers of mites are to be found.
Up to the present time the knapsack type of sprayer has been
used almost exclusively in the ferneries at Pierson. It can be
readily seen that in controlling the two-spotted mite some" other
type of spray machine must be used. The knapsack sprayer will
not produce sufficient pressure to force the spray material be-
neath the bracts, and it is not practical to apply a large quantity
of spray material with a knapsack sprayer. Wheelbarrow spray-
ers or barrel outfits mounted on runners and provided with suf-






Bulletin 234. Twcr-Spottcd 3lit( on Asparagus Plumosuw 19

ficient hose to reach the length of the beds have been used ef-
fectively. A stationary engine spray outfit has been used eco-
nomically in several of the larger ferneries.

SUMMARY

The two-spotted mite. California mite, or green mite is at
present found attacking Asparca us plumosus in only four locali-
ties in the State: Volusia County. Yalaha, Groveland, and Lees-
burg.
It has been found to feed and reproduce on 21 species of weeds
growing in ferneries. The mites prefer nightshade, cudweed,
and tea weed to Asparargus plunioss.
The mites puncture the tissue of the tender shoots beneath
the bracts and withdraw the plant juices, thus dwarfing the
shoots and preventing normal development. Large numbers of
mites cause the plants to turn brown as if they were burned.
During the winter months development progresses slowly and
the mites are rather scarce, but they may be found in the fern-
ery. They are most abundant during the dry warm spring
months, usually April. May, and part of June. When the sum-
mer rains begin the mite population is reduced.
Incubation period for the eggs averaged about six days for
the entire year, but was about four days during the hotter
months. The larval stage averaged about three days and each
of the two nymphal stages three and four days.
Each adult female will lay an average of 70 eggs at the aver-
age rate of three to seven per day.
The average time required for the completion of each genera-
tion was found to be 14.64 days, which indicated that there are
approximately 24 generations a year.
Unfertilized eggs are viable and always produce males. This
is important in the propagation of the mites, for if unfertilized
females become isolated the first eggs will produce males, which
will mate with the females, after which both males and females
will be produced in normal numbers.
Mites travel to a certain extent from plant to plant. Other
workers have shown that they are carried considerable distances
by the wind. In cases where the mites have become established
in other sections of the State dispersion has been traced, with
one exception, to the transportation of infested seedlings.
Observations show that heavy rains decrease the number of







Florida Agricultural Experiment Station


mites and hold them in check from the latter part of June until
the warm dry weather of the succeeding spring.
The mites may be held in check artificially by frequent use of
a sprinkler irrigation system. Growers have used a hose to wet
the plants thoroughly and have controlled heavy infestations of
the mites by this method.
Only two natural enemies of the mites have been observed in
the ferneries at Pierson and these were not abundant enough in
1930 and 1931 to effectively check the mites.
The first step in the control of the mites is the removal of all
weeds in and around the fernery.
The safest and cheapest of the insecticides tested in experi-
ments to control the mites were the white oil emulsions. If the
plants are wet thoroughly with a solution made up of white oil
emulsions, 1-100, at seven-day intervals control of the mites
can be obtained. Solutions of a derris compound will also give
good control of the mites, but the white oils are recommended
because they are much less expensive.
A spray machine, capable of applying 500 to 600 gallons of
spray material to the acre at a pressure of about 200 pounds,
should be used to wet thoroughly all plants and every mite on
them.
A second spray must be applied seven days after the first in
order to destroy the mites that have hatched out after the first
spraying.
LITERATURE CITED

1. EWING, H. E. The common red spider or spider mite. Ore. Agr. Exp.
Sta. Bul. 121: 1-95. 1914.
2. GLOVER, T. Insects frequenting the cotton plant. Rept. U. S. Comm.
Patents: 64-119. 1856.
3. HANSTEIN, R. V. Zur biologie der spinnmilben (Tetranychus Duf.)
Zeits. Pflantzenk. 12: 1-7. 1902.
4. MCGREGOR, E. A. A new spinning mite attacking Asparagus plumosus
in Florida. Proc. Ent. Soc. Wash. 32: 161-163. 1930.
5. MCGREGOR, E. A., AND F. L. McDONOUGH. The red spider on cotton.
U. S. D. A., Contrib. Bur. Ent. Bul. 416: 1-72. 1917.
6. PERKINS, G. H. The red spider (Tetranychus telarius L.). Vt. Agr.
Exp. Sta. Tenth Rept.: 75-86. 1897.
7. STABLER, H. P. Red spider spread by winds. Mo. Bul. Com. Hort.
Calif., 2: 777-780. 1913.
8. WELDON, G. P. Two common orchard mites. The brown mite. The red
spider. Col. Agr. Exp. Sta. Bul. 152: 1-12. 1909.
9. WORSHAM, R. L. The cotton red spider. Ga. Exp. Sta. Bul. 92: 135-
141. 1910.




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