• TABLE OF CONTENTS
HIDE
 Front Cover
 Front Matter
 Distribution
 Review of literature
 Host plants
 Description of the various...
 Life history
 Seasonal history
 Effect of climate on gladiolus...
 Natural enemies
 Summary
 Other thrips found on gladiolu...
 Literature cited






Group Title: Bulletin - University of Florida Agricultural Experiment Station ; 357
Title: The gladiolus thrips in Florida
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE PAGE TEXT
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00026524/00001
 Material Information
Title: The gladiolus thrips in Florida
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 23 p., 1 p. : ill. ; 23 cm.
Language: English
Creator: Wilson, J. W ( John Wallace ), 1902-
Watson, J. R ( Joseph Ralph ), 1874-1946
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1941
 Subjects
Subject: Gladiolus -- Diseases and pests -- Florida   ( lcsh )
Thrips -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Bibliography: p. 24.
Statement of Responsibility: by J.W. Wilson. With notes on other thrips found on gladiolus by J.R. Watson.
General Note: Cover title.
Funding: This collection includes items related to Florida’s environments, ecosystems, and species. It includes the subcollections of Florida Cooperative Fish and Wildlife Research Unit project documents, the Florida Sea Grant technical series, the Florida Geological Survey series, the Howard T. Odum Center for Wetland technical reports, and other entities devoted to the study and preservation of Florida's natural resources.
 Record Information
Bibliographic ID: UF00026524
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000924589
oclc - 18219637
notis - AEN5216

Table of Contents
    Front Cover
        Page 1
    Front Matter
        Page 2
    Distribution
        Page 3
    Review of literature
        Page 4
        Nature of injury
            Page 4
            Page 5
    Host plants
        Page 6
    Description of the various stages
        Page 7
        Page 8
        Page 9
    Life history
        Page 10
        Page 11
        Page 12
    Seasonal history
        Page 13
        Parthenogenesis
            Page 13
    Effect of climate on gladiolus thrips
        Page 14
        Resistant varieties
            Page 14
    Natural enemies
        Page 15
        Control Measures
            Page 15
            Page 16
            Page 17
            Page 18
            Page 19
            Page 20
    Summary
        Page 21
    Other thrips found on gladiolus
        Page 22
        Page 23
    Literature cited
        Page 24
Full Text

BULLETIN 357


UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
WILMON NEWELL, Director
GAINESVILLE, FLORIDA





THE GLADIOLUS THRIPS IN
FLORIDA
By J. W. WILSON



WITH NOTES ON OTHER THRIPS
FOUND ON GLADIOLUS

By J. R. WATSON
















Single Copies Free to Florida Residents upon Request to
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA


MAY, 1941





EXECUTIVE STAFF BOARD OF CONTROL


John J. Tigert, M. A., LL.D., President
of the University3
Wilmon Newell, D.Sc., Director'
Harold Mowry, M. S. A., Asst. Dir.,
Research
W. M. Fifield, M.S., Assistant to Director
J. Francis Cooper, M.S.A., Editor3
Jefferson Thomas, Assistant Editor3
Clyde Beale, A.B.J., Assistant Editor3
Ida Keeling, Cresap, Librarian
Ruby Newhall, Administrative Managers
K. H. Graham, LL.D., Business Manager2
Rachel McQuarrie, Accountants
MAIN STATION, GAINESVILLE
AGRONOMY
W. E. Stokes, M.S., Agronomist'
W. A. Leukel, Ph.D., Agronomist3
Fred H. Hull, Ph.D., Agronomist
G. E. Ritchey, M.S., Associate2
W. A. Carver, Ph.D., Associate
John P. Camp, M.S., Assistant
Roy E. Blaser, M.S., Assistant
Fred A. Clark, B.S.A., Assistant
ANIMAL INDUSTRY
A. L. Shealy, D.V.M., Animal Industrial-
ist3
R. B. Becker, Ph.D., Dairy Husbandman3
E. L. Fouts, Ph.D., Dairy Technologist3
W. M. Neal, Ph.D., Asso. in An. Nutrition
D. A. Sanders, D.V.M., Veterinarian
M. W. Emmel, D.V.M., Veterinarian'
N. R. Mehrhof, M.Agr., Poultry Hus-
bandman"
L. E. Swanson, D.V.M., Parositologist
T. R. Freeman, Ph.D., Asso. in Dairy
Manufactures
D. J. Smith, B.S.A., Asst. An. Husb.
P. T. Dix Arnold, M.S.A., Asst. Dairy
Hus-andman3
L. L. Rusoff, Ph. D., Asst. in An. Nutr.'
L. E. Mull, M.S., Asst. in Dairy Tech.
SOILS
R. V. Allison, Ph.D., Chemist' "
Gaylord M. Volk, M.S., Chemist
F. B. Smith, Ph.D., Microbiologist'
C. E. Bell, Ph.D., Associate Chemist
H. W. Winsor, B.S.A., Assistant Chemist
J. Russell Henderson, M.S.A., Associate'
L. H. Rogers, M.S., Asso. Biochemist
Richard A. Carrigan, B.S., Asst. Chemist
ECONOMICS, AGRICULTURAL
C. V. Noble, Ph.D., Agr. Economist'1
Zach Savage, M.S.A., Associate
A. H. Spurlock, M.S.A., Associate
Max E. Brunk, M.S., Asst. Agr. Econ.
ECONOMICS, HOME
Ouida D. Abbott, Ph.D., Home Econ-
omist,
Ruth Overstreet, R.N., Assistant
R. B. French, Ph.D., Asso. Chemist
ENTOMOLOGY
J. R. Watson, A.M., Entomogist'
A. N. Tissot, Ph.D., Associate
H. E. Bratley, M.S.A., Assistant
HORTICULTURE
G. H. Blackmon. M.S.A., Horticulturist'
A. L. Stahl, Ph.D., Associate
F. S. Jamison, Ph.D., Truck Hort.3
R. J. Wilmot, M.S.A., Fumigation
Specialist
R. D. Dickey, M.S.A., Asst. Horticultursit
J. Carlton Cain, B.S.[A., Assist. Hort.
Victor F. Nettles. M.S.A., Assistant
Lee B. Nash, Ph.D., Asst. Hort.
F. S. Lagasse, Ph.D., Horticulturist2
H. M. Sell. Ph.D., Horticulutrist2
PLANT PATHOLOGY
W. B. Tisdale, Ph.D., Plant Pathologist' 3
George F. Weber, Ph.D., Plant Path.3
L. O. Gratz, Ph.D., Plant Patholigist
Erdman West, M.S., Mycologist
Lillian E. Arnold, M.S., Asst. Botanist


H. P. Adair, Chairman, Jacksonville
W. M. Palmer, Ocala
R. H. Gore, Fort Lauderdale
N. B. Jordan, Quincy
T. T. Scott, Live Oak
J. T. Diamond, Secretary, Tallahassee

BRANCH STATIONS
NORTH FLORIDA STATION, QUINCY
J. D. Warner, M.S., Agron., Act'g. in Chg.
R. R. Kincaid, Ph.D., Asso. Plant Path.
Elliott Whitehurst, B.S.A., Assistant An.
Husbandman
Jesse Reeves, Asst. Agron., Tobacco
CITRUS STATION, LAKE ALFRED
A. F. Camp, Ph.D., Hort. in Charge
John H. Jefferies, Asst. in Cit. Breeding
V C. Jamison, Ph.D., Soils Chem.
Chas. K. Clark, Ph.D., Asst. Chemist
B. R. Fudge, Ph.D., Associate Chemist
W. L. Thompson, B.S., Associate
Entomologist
F. F. Cowart, Ph.D., Asso. Horticulturist
W. W. Lawless, B. S., Ast. Horticulturist
R. K. Voorhees, M.S., Asst. Plant Path.
EVERGLADES STA., BELLE GLADE
J. R. Neller, Ph.D., Biochemist in
Charge.
J. W. Wilson, Sc.D., Entomolgist
F. D. Stevens, B.S. Sugarcane Agron.
Thomas Bregger, Ph.D., Sugarcane
Physiologist
Frederick Boyd, Ph.D., Asst. Agronomist
G. R. Townsend, Ph.D., Plant Pathologist
R. W. Kidder, M.S., Asst. An. Husband-
man
W. T. Forsee, Ph.D., Asso. Chemist
B. S. Clayton, B.S.C.E., Drainage Eng.2
F. S. Andrews, Ph.D., Asso. Truck Hort.
SUB-TROPICAL STA., HOMESTEAD
Geo. D. Ruehle, Ph.D., Associate Plant
Pathologist Acting in Charge
'. J. Lynch, B.S.A., Asst. Horticulturist
E. M. Andersen, Ph.D., Asst. Hort.
W. CENTRAL FLA. STA.,
BROOKSVILLE
W. F. Ward, M.S., Asst. An. Husband-
man in Charge2
RANGE CATTLE STA.,
WAUCHULA
W. S. Kirk, Ph.D., Animal Husbandman
in Charge

FIELD STATIONS
Leesburg
M. N. Walker, Ph.D., Plant Pathologist
in Charge
K. W. Loucks, M.S., Assistant Plant
Pathologist
Plant City
A. N. Brooks, Ph.D., Plant Pathologist
Hastings
A. H. Eddins, Ph.D., Plant Pathologist
E. N. McCubbin, Ph.D., Asso. Truck
Horticulturist
Monticello
Samuel O. Hill, B.S., Asst. Entomologist'
Bradenton
Jos. R. Beckenbach, Ph.D., Truck Horti-
culturist in Charge
David G. Kelbert, Asst. Plant Pathologist
Sanford
R. W. Ruprecht, Ph.D., Chemist in
Charge, Celery Investigations
W. B. Shippy, Ph.D., Asso. Plant Path.
Lakeland
E. S. Ellison, Meteorologist2
B. H. Moore, A.B., Asst. Meteorologist2




'Head of Department
2In cooperation with U. S.
'Cooperative, other divisions, U. of F.







THE GLADIOLUS THRIPS IN FLORIDA
By J. W. WILSON
CONTENTS
PAGE PAGE
Distribution ...._ 3 Natural Enemies ___._ 15
Review of Literature ..------- 4 Control Measures -___._._ ....._- 15
Nature of Injury .._._ _____. 4 Cold Storage __._.___ 15
Host Plants __....-_ 6 Chemical Treatments......-......_ 15
Description of the Various Stages__ 7 Calcium cyanide .--.--_--___.-_ 16
The Egg -.. ...-.... ..... ... 7 Ethylene dichloride-carbon
The Larval Stages --__ 7 tetrachloride -_. --- 17
The Pupal Stages -._...-....--__ 8 Mercuric chloride _._..- _- 18
The Adult ...... ....... ....--- 8 Control Measures on Growing
Life History .-...-..-_..-_.---_ 10 Plants _- ..-.. 18
Seasonal History _...-_-__--.-_ 13 Recommendation for Control 20
Parthenogenesis --.--....... .----____ 13 Summary 21
Effect of Climate on Gladiolus Thrips 14 Other Thrips Found on Gladiolus-- 22
Resistant Varieties _-. _..._..._.. .. 14 Literature Cited -. __.... -... ._-- .... .. 24
The gladiolus thrips, Taeniothrips simplex (Morison), was first
found in the United States near Cleveland, Ohio, during the sum-
mer of 1929 and in Canada near Vineland Station, Ontario, dur-
ing the same summer. This species was described as Physothrips
simplex, new to science, by Guy D. Morison (17)' in 1930. It was
redescribed by Moulton and Steinwenden (18) as Taeniothrips
gladioli in 1931.
DISTRIBUTION
Since 1929 the gladiolus thrips has been found in many coun-
tries of the world. These include Australia, Africa, Canada, the
Hawaiian Islands, and New Zealand. In the United States this
thrips spread rapidly to the gladiolus sections and by 1933 (12) it
had been found in California, Connecticut, Delaware, District of
Columbia, Florida, Georgia, Illinois, Indiana, Iowa, Maine, Mary-
land, Massachusetts, Michigan, Minnesota, New Hampshire, New
Jersey, New York, North Dakota, Ohio, Oregon, Pennsylvania.
Rhode Island, Tennessee, Virginia, West Virginia, and Wisconsin.
That the gladiolus thrips spread so rapidly is in all probability
due to the fact that the thrips attacks the corms as well as the
plants and was shipped to all parts of the country on infested
corms.
The gladious thrips was first found in Florida early in 1932
(26). Within a short time the Entomology Department of the
Agricultural Experiment Station at Gainesville received speci-
mens from Bradenton, Stuart and Sanford, indicating that the
thrips was already well established and widely scattered in the
state. Since 1932 it has been found in all parts of the state where
gladiolus is grown on a commercial scale.

'Italic figures in parentheses refer to "Literature Cited" in the back
of this bulletin.
Acknowledgements.-The writer is indebted to Rohm and Haas
Company, Grasselli Chemical Company, Apex Chemical Company and
the Atlas Powder Company for furnishing some of the insecticides used.






Agricultural Experiment Station


REVIEW OF LITERATURE
A number of entomologists in different parts of the country
have studied the gladiolus thrips and measures for its control.
Dunstan (2) recommended in 1931 the use of a molasses-paris
green bait sprayed on the plants as a means of control. An
editorial (p. 23) in the May 5, 1932, issue of the Florida Review
suggests the use of naphthalene flakes on stored corms. Fumiga-
tion with ethylene dichloride-carbon tetrachloride or calcium
cyanide, and dipping in mercuric chloride or hot water were
also suggested. McDaniel (14) working in Michigan recom-
mended carbon bisulphide emulsion as a dip for thrips on the
corms. Evans (4) also found the carbon bisulphide emulsion to be
effective in thrips control. Gambrell (6, 7, and 8) and Hamilton
(9 and 10) have reported on life history and control measures in
New York and New Jersey. McDaniel (14 and 15) suggested lead
arsenate 32 oz., derrisol 4 oz., glue 1 1b. and water 10 gallons as
a spray for the control of thrips on the gladiolus plants. Smith
and Weigel (25), Smith (22), Smith and Nelson (23), Smith and
Richardson (24), Richardson and Nelson (21), all of the United
States Department of Agriculture, have published detailed re-
ports on the life history and control of the gladiolus thrips. Fol-
lowing his work on sprays in 1932 and 1933 Richardson (20) pub-
lished an account of his investigation on derris, nicotine, paris
green and other poisons in combination with molasses. He con-
cluded that it is very important to maintain a toxic spray residue
on the foilage. Paris green residues retained considerable tox-
icity after 0.6 inch of precipitation. Tartar emetic at 1 to 400
with a 3 percent molasses solution was found to be very toxic to
adult thrips. In order to avoid arsenical injury Nelson (19) tried
a number of tartar emetic concentrations. He found tartar eme-
tic 4 pounds, brown sugar 16 pounds, and 100 gallons of water
gave a control equal to the paris green spray and did not injure
the gladiolus plant.
NATURE OF INJURY
The injury caused by the gladiolus thrips is of three types:
1, injury to the plant and flower spike; 2, indirect injury to the
corms by reducing the vigor of the plants which in turn produce
smaller corms, and 3, direct injury to the corms.
Injury to the plant is caused by feeding of both the adults and
larvae. The first indication of the presence of the thrips is small
silvery white scars at the base of the plant (Fig. 1). As the num-






Agricultural Experiment Station


REVIEW OF LITERATURE
A number of entomologists in different parts of the country
have studied the gladiolus thrips and measures for its control.
Dunstan (2) recommended in 1931 the use of a molasses-paris
green bait sprayed on the plants as a means of control. An
editorial (p. 23) in the May 5, 1932, issue of the Florida Review
suggests the use of naphthalene flakes on stored corms. Fumiga-
tion with ethylene dichloride-carbon tetrachloride or calcium
cyanide, and dipping in mercuric chloride or hot water were
also suggested. McDaniel (14) working in Michigan recom-
mended carbon bisulphide emulsion as a dip for thrips on the
corms. Evans (4) also found the carbon bisulphide emulsion to be
effective in thrips control. Gambrell (6, 7, and 8) and Hamilton
(9 and 10) have reported on life history and control measures in
New York and New Jersey. McDaniel (14 and 15) suggested lead
arsenate 32 oz., derrisol 4 oz., glue 1 1b. and water 10 gallons as
a spray for the control of thrips on the gladiolus plants. Smith
and Weigel (25), Smith (22), Smith and Nelson (23), Smith and
Richardson (24), Richardson and Nelson (21), all of the United
States Department of Agriculture, have published detailed re-
ports on the life history and control of the gladiolus thrips. Fol-
lowing his work on sprays in 1932 and 1933 Richardson (20) pub-
lished an account of his investigation on derris, nicotine, paris
green and other poisons in combination with molasses. He con-
cluded that it is very important to maintain a toxic spray residue
on the foilage. Paris green residues retained considerable tox-
icity after 0.6 inch of precipitation. Tartar emetic at 1 to 400
with a 3 percent molasses solution was found to be very toxic to
adult thrips. In order to avoid arsenical injury Nelson (19) tried
a number of tartar emetic concentrations. He found tartar eme-
tic 4 pounds, brown sugar 16 pounds, and 100 gallons of water
gave a control equal to the paris green spray and did not injure
the gladiolus plant.
NATURE OF INJURY
The injury caused by the gladiolus thrips is of three types:
1, injury to the plant and flower spike; 2, indirect injury to the
corms by reducing the vigor of the plants which in turn produce
smaller corms, and 3, direct injury to the corms.
Injury to the plant is caused by feeding of both the adults and
larvae. The first indication of the presence of the thrips is small
silvery white scars at the base of the plant (Fig. 1). As the num-





The Gladiolus Thrips in Florida


ber of thrips increases and as the plant grows, larger areas of
silvery white are noticed. When the flower spike appears the
thrips attack the buds, producing scarred and deformed florets
which do not open normally in cases of severe attacks. These


J


Fig. 1.-Injury (to plant on left) caused by gladiolus thrips to leaves and
blossom bud of gladiolus.






Agricultural Experiment Station


white scars are produced by the sucking mouthparts of the adult
and larval thrips. The plant surface is first broken by the jaws.
The long maxillary stylets are then thrust into the deeper cells
and the plant juices are sucked into the digestive tract.
Severe attacks of the thrips reduce the leaf area available for
producing plant food, thus reducing the vigor of the plant and its
ability to produce new corms.
The injury to corms is not as severe in Florida as in other
parts of the country, although serious damage sometimes follows
improper care of the corms. Most serious cases of this type of
injury have been observed on corms dug during January or Feb-
ruary and left in open storage during the time thrips are most
abundant in the field.

HOST PLANTS
The gladiolus thrips has been reported to feed and reproduce
on foilage of the following closely related plants: tiger-flower
(Tigridia), Tritonia, Kniphofia sp., Japanese iris and on the stored
corms of Spanish iris (Weigel and Smith (28)). In Ohio the adults
have been collected from a number of plants growing near
heavily infested fields or from plants in greenhouse near heavily
infested gladiolus plants, but in no case has the gladiolus thrips
been observed breeding on any other plants than those named
above (Herr 11). Wild iris growing beside the roadways in
many parts of Florida has been examined for gladiolus thrips,
but none has yet been found. During 1934 and 1935 the follow-
ing plants of the families Amaryllidaceae and Iridaceae were
grown in the Experiment Station greenhouses at Leesburg; Euchar-
is grandiflora, Crinum powelli, Narcissus variety Cleopatra, Ixia sp.
Marcia gracilis, Sparaxis sp., Freesia sp., and Tritonia crocata. These
plants were artificially infested with gladiolus thrips several
times but the insects did not complete their life cycle on any of
them.
Near a field of very heavily infested gladiolus at Belle Glade
the gladiolus thrips has been observed on aster, calendula and
crow-foot grass ( Eleusine indica). The presence of the gladiolus
thrips on these plants was probably accidental, as the adult thrips
was the only stage collected.







The Gladiolus Thrips in Florida


DESCRIPTION OF THE VARIOUS STAGES
During its development the gladiolus thrips passes through
six stages; the egg, two larval stages, two pupal stages and the
adult.
THE EGG
The egg (Fig. 2) is opaque white, smooth, and bean shaped,
and measures about 0.3 mm. in length and 0.11 to 0.19 mm. in
diameter. Eggs may be deposited in the corms,
but in Florida the gladiolus thrips breeds on the
growing plant the year round. The majority of
the eggs are deposited just beneath the outer cell
layer between the veins of the leaves. When the
infestation is heavy, long rows of eggs may be ob-
Fig. 2.-Egg served, with the aid of a microscope, by raising
of the glad-
iolus thrips the outer cell layer of the leaf.
(X70).
THE LARVAL STAGES
The mature embryo within the unbroken, flexible egg shell
forces the fore part of the body outside the leaf surface. The
milky-white larva, measuring about 0.5 mm. (a fiftieth of an
inch) in length and 0.15 mm. in width, then breaks the shell and
emerges. Feeding begins after a
short time and the body color
changes to a light yellow which is
maintained through the larval and
pupal stages. When the first stage
larva reaches its full size it passes
Through a short quiescent period.
At the end of this time the skin
splits down the back. The second
stage larva (Fig. 3) pulls itself out
and begins feeding again. The two
L larval stages differ very little ex-
cept in size. The second stage lar-
va, when it has reached its full
size, is about as large as the wing-
ed adult.

Both larval stages move about
the plant freely but are most fre-
)A quently found congregated at the
base of the leaves beneath the part
wrapped around the central portion
Sof the plant or beneath the bracts
Fig. 3.--Second larval stageinii
f thi olrlin,, c h rn,, (fl3u4 around the individual flower buds.






Agricultural Experiment Station


Fig. 4.-First stage pupa 1,
of the gladiolus thrips Fig. 5.-Second stage pupa of the
(x 72). gladiolus thrips (x 79).
THE PUPAL STAGES
At the end of the second larval stage the insect again passes
through a short quiescent period and molting process. The
first pupal stage (Fig. 4) is distinguished by having the antennae
projecting forward as in the larval stage and by the short wing
pads. This instar measures 1.12 mm. in length and 0.3 mm. in
width. The second pupal stage (Fig. 5) has the antennae folded
back over the body and the wing pads are much longer than
in the preceding stage. It measures 1.19 mm. in length and
0.32 mm. in width. Both pupal stages move about slowly when
disturbed but there is no feeding during these stages.
THE ADULT
When the adult first emerges it is milky white in color, but
soon turns dark brown and begins feeding. The antennae are
dark brown except the third segment which is light brown. The
wings when not in use are folded back over the abdomen and
have a transverse light band near the base. The female (Fig. 6)
is slightly larger (1.6 to 1.7 mm. long as compared with 1.1 to 1.3
mm.) and darker than the male.





The Gladiolus Thrips in Florida


A


8
Fig. 6.-A, adult female gladiolus thrips (Taeniothrips simplex Morison)
dorsal view. B, ventral view of segments six to 10, showing the oviposi-
tor. Both drawings enlarged 98 times.





Agricultural Experiment Station


LIFE HISTORY
During the years 1933 to 1936 life history studies were con-
ducted in an open insectary at Leesburg. A thermograph on
the table where the life history cages were kept supplied a rec-
ord of the temperature. Fresh gladiolus leaves were supplied
each 24 hours to pairs of adult thrips in cotton stoppered vials.
The eggs hatching from these leaves were recorded and the
newly hatched larvae were transferred to cotton stoppered vials.
The developing larvae and pupae were also examined and sup-
plied with fresh food daily. The cotton stoppers were covered
with small pieces of silk to prevent the thrips becoming en-
tangled in the cotton. These insectary studies were supple-
mented by field observations which showed that the records
obtained under the artificial insectary conditions are depend-
able.

As is the case with most insects, the duration of the various
stages was influenced greatly by temperature. From two to five
days after emergence the adult females began depositing eggs.
In Table 1 the effect of temperature upon the number of eggs
deposited is clearly shown. At average temperatures of below
80' F. the average number of eggs per female was 50 or more
while at average temperatures above 80 F. the number of eggs
per female dropped to 35.5.

The average temperatures given in the tables were obtained
by averaging the maximum and minimum for each day the in-
dividual was observed. These daily averages were summed to
obtain the average for the period of the individual's develop-
ment. Under insectary conditions in Florida there are many
more days with an average temperature of 70' F. or above than
with average temperatures under 700 F., which explains the
much larger number of observations made in the higher tem-
perature ranges.

During periods when the average temperatures were 70' F.
or higher the eggs required three to seven days to hatch. Dur-
ing the cooler months of the year four to 11 days were required
for the eggs to hatch. There was one period of five days in De-
cember, 1934, when the average temperature was below 550 F.
Female thrips did not deposit eggs during this period and eggs
deposited just prior to it failed to hatch.






The Gladiolus Thrips in Florida


TABLE 1.-Maximum, Minimum and Average Number of Eggs Deposit-
ed per Individual in Insectary at Leesburg 1933-361.
Average Temp- Individuals Number of Eggs Deposited per Individual
erature "F Observed Maximum Minimum Average
55-59 17 169 34 64.6
60-64 30 166 20 64.7
65-69 19 178 23 65.7
70-74 26 144 19 55.2
75-79 75 154 8 50.5
80-85 130 146 3 35.5

Mean temperature-70' F. Mean number eggs-56.1.
'Under conditions of controlled temperature the figures would
probably be quite different, but these figures do indicate the trend.

Shortly after hatching the young larva begins feeding.
After feeding for about two days the larva passes through a
short quiescent period, then molts or sheds its skin. The two
larval stages are characterized by voracious feeding and rapid
growth. These two stages require from three to 12 days, de-
pending upon the temperature.
The first and second pupal stages are completed in three
to nine days.
In Table 2 the data for the various developmental stages
are summarized. The adult female thrips mates soon after the
last molt and feeds for two or more days before egg laying be-
gins. In Table 2 the duration of this preoviposition period is
included in the calculation of the total duration of all stages.
Thus the complete life cycle, from egg to egg, requires 13 to 36
days. Twenty generations of thrips were reared in the insect-
ary from August, 1933, to August, 1934. However, in the field
the various generations overlap to such an extent that no dis-
tinct broods can be distinguished.
As is the case in other stages, the duration of the adult
stage is influenced greatly by temperature. The data for this
stage are summarized in Table 3. At average temperatures of 800
to 85' F. the average length of female life was 15.45 days. This
short life at higher temperatures is accompanied by a small
number of eggs deposited. From insectary and field observa-
tions, optimum conditions for the development of gladiolus
thrips are the dry and warm periods of the year, but not the
hot moist periods.






Agricultural Experiment Station


TABLE 2.-Duration of Development Period of Immature Stages of
Gladiolus Thrips Reared in Insectary at Leesburg, Florida.
Average Temp- Number Individ- Period of Development in Days
erature F uals Observed Maximum Minimum Average
55-59 1099 11 5 7.66
60-64 1943 11 4 7.16
Egg 65-69 1248 11 4 6.86
70-74 1817 7 3 5.38
75-79 3572 5 3 3.86
80-85 3951 5 3 3.58
55-59 14 12 7 8.72
60-64 13 11 6 7.81
Larva 65-69 26 9 5 6.85
70-74 49 7 4 5.33
75-79 71 6 3 4.59
80-85 137 6 3 4.24
55-59 3 9 6 7.00
60-64 11 8 6 6.77
Pupa 65-69 12 8 4 6.79
70-74 47 7 4 4.66
75-79 83 5 3 3.77
80-85 140 4 3 3.30
55-59 10 28 25 26.11
Total 60-64 15 36 23 28.75
all 65-69 27 26 19 22.08
stages 70-74 17 21 16 18.27
75-79 63 17 14 14.89
80-85 118 15 13 13.87
TABLE 3.-Length of Life of Male and Female Gladiolus Thrips Reared
in Insectary at Leesburg, 1933-36.
Average Temp- Number Individ- Duration in Days
erature F uals Observed Maximum Minimum Average
55-59 6 46.00
60-64 26 50 18 35.66
Male 65-69 36 57 22 35.45
70-74 37 37 18 25.78
75-79 93 24 10 19.13
80-85 105 21 9 12.83
55-59
60-64 26 81 36 50.10
Female 65-69 36 69 18 35.90
70-74 30 31 23 27.35
75-79 93 26 14 19.36
80-85 108 21 10 15.14
55-59 6 27.60
60-64 26 64 18 33.52
Oviposi- 65-69 36 48 9 21.26
tion 70-74 30 21 17 18.27
period 75-79 93 17 5 11.76
80-85 108 19 2 9.30
55-59
60-64 26 16 3 11.42
Postovi- 65-69 36 13 5 10.23
position 70-74 30 7 3 5.00
period 75-79 93 12 2 4.65
80-85 108 6 1 3.89





The Gladiolus Thrips in Florida


SEASONAL HISTORY
Because of unfavorable growing conditions, gladioli are not
grown commercially during the summer in Florida. Climatic
conditions are also unfavorable for the development of the
gladiolus thrips during this season, as will be shown later. The
gladiolus thrips may be found in small numbers on volunteer
plants' in commercial fields or on 'plants grown in home gar-
dens. Near Bradenton thrips were observed on plants produced
from a pile of discarded corms and cormels three years after
gladiolus had last been grown within several miles of that vicin-
ity. That thrips pass the summer principally on vounte r
plants is shown by observations made during the summers of
1933 and 1936, in which they were commonly found on such
plants. On the other hand, by September none could be found
on corms, even when stored at air temperatures. One hun-
dred adult thrips were sealed in each of 10 paper sacks with
gladiolus corms and stored in a screened insectary. Examina-
tion of the corms after four months of storage showed that the
adults had fed on the corms and produced some progeny but no
living thrips of any stage were found at the time of examina-
tion.
During the fall the thrips migrate to the new plantings and
begin to multiply. Feeding and reproduction continue at a
slower rate during December and January, except during short
periods of very low temperatures when all activity ceases.
Usually February to May are dry, warm months. These cli-
matic conditions are favorable for thrips development and the
population increases rapidly. It is usually during these months
that serious economic losses result from thrips attack.

PARTHENOGENESIS
During the course of the life history studies 26 unmated fe-
males were observed. All of these females laid eggs from
which male thrips always developed. Since females live long
enough to mate with their own male progeny it is possible for a
single female to start an infestation. However, males and fe-
males are usually present in about equal numbers. Of 485 indi-
viduals reared from mated females 47.6 per cent were females
and 52.4 percent were males. Smith and Nelson (3) report that
32.5 percent of 874 individuals reared from mated females were
males.





The Gladiolus Thrips in Florida


SEASONAL HISTORY
Because of unfavorable growing conditions, gladioli are not
grown commercially during the summer in Florida. Climatic
conditions are also unfavorable for the development of the
gladiolus thrips during this season, as will be shown later. The
gladiolus thrips may be found in small numbers on volunteer
plants' in commercial fields or on 'plants grown in home gar-
dens. Near Bradenton thrips were observed on plants produced
from a pile of discarded corms and cormels three years after
gladiolus had last been grown within several miles of that vicin-
ity. That thrips pass the summer principally on vounte r
plants is shown by observations made during the summers of
1933 and 1936, in which they were commonly found on such
plants. On the other hand, by September none could be found
on corms, even when stored at air temperatures. One hun-
dred adult thrips were sealed in each of 10 paper sacks with
gladiolus corms and stored in a screened insectary. Examina-
tion of the corms after four months of storage showed that the
adults had fed on the corms and produced some progeny but no
living thrips of any stage were found at the time of examina-
tion.
During the fall the thrips migrate to the new plantings and
begin to multiply. Feeding and reproduction continue at a
slower rate during December and January, except during short
periods of very low temperatures when all activity ceases.
Usually February to May are dry, warm months. These cli-
matic conditions are favorable for thrips development and the
population increases rapidly. It is usually during these months
that serious economic losses result from thrips attack.

PARTHENOGENESIS
During the course of the life history studies 26 unmated fe-
males were observed. All of these females laid eggs from
which male thrips always developed. Since females live long
enough to mate with their own male progeny it is possible for a
single female to start an infestation. However, males and fe-
males are usually present in about equal numbers. Of 485 indi-
viduals reared from mated females 47.6 per cent were females
and 52.4 percent were males. Smith and Nelson (3) report that
32.5 percent of 874 individuals reared from mated females were
males.






Agricultural Experiment Station


EFFECT OF CLIMATE ON GLADIOLUS THRIPS
As has previously been pointed out the duration of the
various developmental stages of the gladiolus thrips is very
markedly influenced by the prevailing temperature. In Table 3
it is shown that during periods when the average temperatures
are above 800 F. the oviposition period and the total length of
life are much shorter than when the average temperatures are
below 80 F. Furthermore, a smaller number of eggs are de-
posited during periods when temperatures are 80 or over, as
shown in Table 1. This tendency was so marked that it was dif-
ficult to maintain the life history studies in the insectary during
September.
In addition, the frequent heavy rains which usually occur
during June to September wash many thrips from the plants and
destroy large numbers of them. In fields previously heavily in-
fested with thrips it becomes very difficult to find thrips after
the summer rains begin. Thus heavy rains and high tempera-
tures combine to reduce the number of thrips during the summer
months.
During December 1934 the average temperature at Leesburg
was 57.5 F. and freezing temperatures occurred on the nights
of December 12 and 13. Adult thrips in the insectary survived
these low temperatures but ceased egg laying. Eggs in the in-
sectary during this period of low temperatures also failed to
hatch. At infrequent intervals temperatures low enough to de-
stroy the gladious plants occur in many sections of the state, but
the adult thrips are able to survive short periods of freezing tem-
peratures and transfer to the new plants that come up after
these cold periods have passed.

RESISTANT VARIETIES
Some varieties of gladious have been observed to be resist-
ant to thrips attack. These include Giant Nymph, America, and
Mrs. Frank Pendleton. Herr (11) has correlated this resistance
with the length of time from planting to blooming. In general,
the late-blooming varieties were more severely injured than the
early-blooming varieties.
In a commercial planting at Port Mayaca the varieties Shay-
lor, Golden Measure and Golden Eagle appeared to suffer less
damage than Picardy and the red varieties.






Agricultural Experiment Station


EFFECT OF CLIMATE ON GLADIOLUS THRIPS
As has previously been pointed out the duration of the
various developmental stages of the gladiolus thrips is very
markedly influenced by the prevailing temperature. In Table 3
it is shown that during periods when the average temperatures
are above 800 F. the oviposition period and the total length of
life are much shorter than when the average temperatures are
below 80 F. Furthermore, a smaller number of eggs are de-
posited during periods when temperatures are 80 or over, as
shown in Table 1. This tendency was so marked that it was dif-
ficult to maintain the life history studies in the insectary during
September.
In addition, the frequent heavy rains which usually occur
during June to September wash many thrips from the plants and
destroy large numbers of them. In fields previously heavily in-
fested with thrips it becomes very difficult to find thrips after
the summer rains begin. Thus heavy rains and high tempera-
tures combine to reduce the number of thrips during the summer
months.
During December 1934 the average temperature at Leesburg
was 57.5 F. and freezing temperatures occurred on the nights
of December 12 and 13. Adult thrips in the insectary survived
these low temperatures but ceased egg laying. Eggs in the in-
sectary during this period of low temperatures also failed to
hatch. At infrequent intervals temperatures low enough to de-
stroy the gladious plants occur in many sections of the state, but
the adult thrips are able to survive short periods of freezing tem-
peratures and transfer to the new plants that come up after
these cold periods have passed.

RESISTANT VARIETIES
Some varieties of gladious have been observed to be resist-
ant to thrips attack. These include Giant Nymph, America, and
Mrs. Frank Pendleton. Herr (11) has correlated this resistance
with the length of time from planting to blooming. In general,
the late-blooming varieties were more severely injured than the
early-blooming varieties.
In a commercial planting at Port Mayaca the varieties Shay-
lor, Golden Measure and Golden Eagle appeared to suffer less
damage than Picardy and the red varieties.






The Gladiolus Thrips in Florida


NATURAL ENEMIES
The gladiolus thrips seems remarkably free of natural ene-
mies. A predacious bug, Orius insidiosus (Say), has been found
feeding on gladiolus thrips in other sections of the country but
it does not destroy enough thrips to control a well established
infestation. McKenzie (16) reports that the parasite Thripoctenus
russelli Crawf. has been taken feeding on gladiolus thrips in Cali-
fornia.
The ladybeetles Ceratomegilla fuscilabris floridana (Leng) and
Cycloneda sanguinea immaculate (Fab.) have been observed feeding
on adult and larval gladiolus thrips at Belle Glade, Florida. The
adult thrips were very abundant at the time. A single adult of
the first named beetle captured and devoured six adult and one
larval thrips within a 15 minute period. The ladybeetle did not
move from one thrips to the next but passed over most of the
thrips on the leaf. In moving about over the gladiolus plant the
ladybeetle would occasionally distrub a thrips. This moving
thrips would be seized and devoured on the spot. Then the lady-
beetle would resume its nervous running about over the plant,
apparently unaware of the large number of thrips which were
not distrubed by its movements.
CONTROL MEASURES
COLD STORAGE
Most commercially grown corms are placed in storage at 380
to 400 F. after a short curing period. It had been observed that
corms heavily infested with thrips when placed in storage ap-
peared to be free of thrips after three or four months of storage
at this temperature. To test this point four samples of 25 corms
each were examined for thrips after three months in commercial
storage during the summer of 1938. The corms were heavily
infested when placed in storage and showed considerable injury
from feeding and egg laying. No live thrips of any stage were
found when the subsequent examination was made. The corms
were kept in the laboratory and examined at frequent intervals
for four weeks after removal from storage. No larval thrips de-
veloped from eggs deposited in these corms. Numerous other
examinations of corms removed from cold storage have been
made but no live thrips have been taken from corms treated in
this manner. Thus the practice of storing the corms at 38 to
400 F. during the inactive period is an effective control for the
gladiolus thrips.






The Gladiolus Thrips in Florida


NATURAL ENEMIES
The gladiolus thrips seems remarkably free of natural ene-
mies. A predacious bug, Orius insidiosus (Say), has been found
feeding on gladiolus thrips in other sections of the country but
it does not destroy enough thrips to control a well established
infestation. McKenzie (16) reports that the parasite Thripoctenus
russelli Crawf. has been taken feeding on gladiolus thrips in Cali-
fornia.
The ladybeetles Ceratomegilla fuscilabris floridana (Leng) and
Cycloneda sanguinea immaculate (Fab.) have been observed feeding
on adult and larval gladiolus thrips at Belle Glade, Florida. The
adult thrips were very abundant at the time. A single adult of
the first named beetle captured and devoured six adult and one
larval thrips within a 15 minute period. The ladybeetle did not
move from one thrips to the next but passed over most of the
thrips on the leaf. In moving about over the gladiolus plant the
ladybeetle would occasionally distrub a thrips. This moving
thrips would be seized and devoured on the spot. Then the lady-
beetle would resume its nervous running about over the plant,
apparently unaware of the large number of thrips which were
not distrubed by its movements.
CONTROL MEASURES
COLD STORAGE
Most commercially grown corms are placed in storage at 380
to 400 F. after a short curing period. It had been observed that
corms heavily infested with thrips when placed in storage ap-
peared to be free of thrips after three or four months of storage
at this temperature. To test this point four samples of 25 corms
each were examined for thrips after three months in commercial
storage during the summer of 1938. The corms were heavily
infested when placed in storage and showed considerable injury
from feeding and egg laying. No live thrips of any stage were
found when the subsequent examination was made. The corms
were kept in the laboratory and examined at frequent intervals
for four weeks after removal from storage. No larval thrips de-
veloped from eggs deposited in these corms. Numerous other
examinations of corms removed from cold storage have been
made but no live thrips have been taken from corms treated in
this manner. Thus the practice of storing the corms at 38 to
400 F. during the inactive period is an effective control for the
gladiolus thrips.





Agricultural Experiment Station


CHEMICAL TREATMENTS
In cases where a quick control of thrips on corms is desired,
three chemicals may be used: (1) Calcium cyanide, (2) ethylene
dichloride-carbon tetrachloride, and (3) mercuric chloride. Re-
sults of tests conducted with these materials are given in Table
4. Corms dug in February and held in common storage until
May, which became heavily infested with thrips, were used in
these tests. Fifty corms were used for each treatment and were
planted afterward for observation of the effect of the treatment
on the corms. All treatments were conducted at room tempera-
ture.

If either of the two fumigants, calcium cyanide or ethylene
dichoride-carbon tetrachloride, is to be used, several precautions
must be exercised to make their use efficient. First, an air-tight
fumigation chamber must be available. Second, the cubic con-
tents of the chamber must be determined and the proper amount
of the fumigant weighed or measured. Third, the corms should
be placed in shallow trays with wire bottoms and cleats so that
when stacked, air can circulate between the individual trays.
Best results will be obtained if the filled trays take up no more
than three-fourth of the available space. An electric fan used
in the room during the fumigation will give a more uniform dis-
tribution of the fumigant.

Calcium Cyanide.-As shown in Table 4, complete control of
thrips was obtained with a dosage of three ounces of calcium
cyanide to 1,000 cubic feet of space and an exposure of three
hours. The crude "A" dust (44% active calcium cyanide) should
be used, as this fine powder produces a lethal concentration of
hydrocyanic acid gas more rapidly than the granular forms. It
must be remembered that this is a very deadly poison gas. The
container in which the calcium cyanide is kept should be opened
and the dust weighed in a well ventilated room. It is preferable
for two persons to work together while handling the dust. After
the material is weighed it should be scattered in a thin layer on
the floor of the fumigation room, beginning at the back and work-
ing toward the open door. Close the door, post a warning sign,
and allow no one to enter during the fumigation period or until
the room has been thoroughly ventilated. Rooms which adjoin
occupied dwellings or animal shelters should not be used as
fumigation chambers.







The Gladiolus Thrips in Florida


Because this gas does not destroy the eggs of the gladiolus
thrips in the corms, the fumigation should be repeated once or
perhaps twice at 10-day intervals. This interval will allow time
enough for the eggs to hatch but not for the larvae to reach ma-
turity.

TABLE 4.-Results of Treatments of Corms for Control of the Gladiolus
Thrips.


Material


Number
Dosage of
Tests


Calcium 3 oz. to
cyanide 1000 cu. ft.
Calcium 3 oz to
cyanide 1000 cu. ft.
Calcium 3 oz. to
cyanide 1000 cu. ft.
Calcium 5 oz. to
cyanide 1000 cu. ft.
Calcium 5 oz. to
cyanide 1000 cu. ft.
Calcium 5 oz. to
cyanide 1000 cu. ft.
Calcium 7 oz. to
cyanide 1000 cu. ft.
Calcium 7 oz. to
cyanide 1000 cu. ft.
Calcium 7 oz. to
cyanide 1000 cu. ft.
Ethylene 14 lbs. to
dichloride- 1000 cu. ft.
carbon
tetrachloride
Mercuric 1 oz. to
chloride 7Y2 gal.
water


1


Duration
of Treat-
ment in
Hours
2


Number Average Number
Thrips Percent Thrips
Counted Mort'lty Counted
in Check
27 96.29 33


Percent
Mort'lty
in Check
3.03


3 82 100.00 60 0


1 4


38 100.00 32 0


2 23 100.00 36 0

3 92 100.00 71 0

4 46 100.00 38 0

2 31 93.54 41 2.44

3 92 100.00 82 0

4 41 100.00 31 0


12 178
18 130


97.75
100.00


3 18 114 100.00 83 0


Treatment with calcium cyanide did not injure the corms.
When planted in the field, the corms from all dosages and ex-
posures grew normally.
Ethylene dichloride-carbon tetrachloride.-A mixture of these
materials consisting of three parts ethylene dichloride and one
part carbon tetrachloride should be used at the rate of 14 pounds
(5 quarts) to each 1,000 cubic feet of space, with an exposure of
18 hours. This mixture is a nonexplosive liquid which volatilizes
at ordinary room temperature, producing a poisonous gas that is
heavier than air. Fumigation should not be attempted when the






Agricultural Experiment Station


temperature is below 60 F. Since the gas is heavier than air
the liquid should be poured into shallow pans placed on top of
the stacked trays. This material kills the eggs of the gladiolus
thrips as well as other stages. For this reason only one fumiga-
tion is required.
Corms subjected to fumigation with ethylene dichloride-car-
bon tetrachloride were not injured.
Mercuric Chloride.-This chemical is a deadly poison and
should be handled carefully. It corrodes metals and should be
used only in glass, earthenware or wooden containers. When the
corms are submerged for 18 hours in a solution of one ounce to
71/ gallons of water all stages, including the egg, of the gladiolus
thrips are killed. Because a large part of the mercuric chloride
is absorbed by the corms a fresh solution should be prepared for
each batch of corms.
Corms treated with this solution required a slightly longer
time to come up than untreated corms, but were not affected
-otherwise. Mercuric chloride has an advantage over the fumi-
gants in that it is also a fungicide.

CONTROL MEASURES ON GROWING PLANTS
In the field experiments, 200 corms of Alice Tiplady variety
were planted in two-row plots with fivefoot intervals between
plots. Treatments were arranged in randomized blocks and re-
plicated four times, except the 1938 planting at Plant City which
was replicated only three times. The bloom spikes were cut
three times a week and the flowers were separated into two
grades: No. 1 grade florets without any thrips marks or occas-
ional inconspicuous ones; No. 2 grade florets showing perceptible
thrips injury. The data for the 1938 spring crop grown at Plant
City, the 1939 fall crop and the 1940 spring crop grown at Belle
Glade are presented. During other years the plots were not uni-
formly infested with thrips. The data were subjected to analysis
of variance according to Fisher (5) and differences required for
significance are given. The spray materials were applied at
seven-day intervals, except in the case of the 1940 spring crop
when the thrips infestation became so heavy that it was necessary
to apply the sprays twice a week.
From the results given in Table 5 it is seen that only the
tartar emetic and paris green bait sprays were significantly better







The Gladiolus Thrips in Florida


than the untreated check. The paris green bait gave a slightly
better yield of Grade 1 spikes but the gladiolus plant was severely
injured. The nicotine sulfate-molasses spray also severely in-
jured the plants. Seven applications of the spray materials were
made, beginning March 21.

The experiments during the fall of 1939 at Belle Glade con-
sisted of two treatments, tartar emetic and an aliphatic thiocyan-
ate, and a check. These treatments were replicated four times.
Four applications of the spray materials were made beginning
December 13. As shown in Table 6 the tartar emetic spray was
significantly better than either the aliphatic thiocyanate or the
check.

During the spring of 1940 a very severe infestation of thrips
developed so that no salable spikes were produced in any of the
plots excepting the plots sprayed with tartar emetic. The thrips
became so numerous that it was necessary to apply the spray


TABLE 5.-Results of Field Experiments Conducted at Plant City, Flor-
ida, During the Spring of 1938.


Spray Material
Tartar emetic
Brown sugar
Paris green
Brown sugar
Nicotine sulfate
Blackstrap molasses
Proprietary aliphatic thiocyanate
Spreader
Proprietary rotenone spray
Spreader
Proprietary pyrethrum spray
Spreader
Proprietary aliphatic thiocyanate
Spreader
Rotenone dust (0.75% rotenone)


Quantity per 100
Gallons Water
4 lbs.
16 "
1 "
66 "
1 quart
5 gal.
21 fluid oz.
5.6 "
1 quart
6.5 fluid oz.
1 quart
6.5 fluid oz.
1 quart
2 quarts


Mean Percent of
Grade 1 Spikes


Untreated check 45.6

Differences of 41.47% are required between any two means for sig-
nificance at the 5% point.

materials twice a week instead of once as had been the practice
on the other crops. A total of 10 applications of the spray ma-
terial was necessary to produce 77.01% of Grade 1 spikes in the
plots treated with tartar emetic.






Agricultural Experiment Station


TABLE 6.-RESULTS OF FIELD EXPERIMENTS CONDUCTED AT BELLE GLADE, FLORIDA,
DURING THE FALL OF 1939.
Quantity per 100 Mean Percent of
Spray Material Gallons Water Grade 1 Spikes
Tartar emetic 4 Ibs.
Brown sugar 16 Ibs. 92.1
Proprietary aliphatic thiocyanate 1 quart
Spreader 2 quarts 54.7
Untreated check 44.7
Differences of 29.49% are required between means for significance
at the 5% point.
RECOMMENDATIONS FOR CONTROL
The corms should be removed from the field and cleaned as
soon as possible after digging. The commercial practice of storing
the corms at 380 to 400 F. for three to four months to retard sprout-
ing also prevents development of the thrips.
If it becomes necessary to treat the corms, they may be
fumigated with either ethylene dichloride-carbon tetrachloride
using 14 pounds per 1,000 cubic feet of space for 18 hours or
calcium cyanide at the rate of three ounces per 1,000 cubic feet
for three hours. Both of these materials are dangerous poisons.
Precautions previously given should be carefully followed. The
corms also may be dipped in a solution of mercuric chloride 1
oz. to 71/ gallons of water for 18 hours.
The spray material that has consistently given the best con-
trol of the gladiolus thrips on the plants consists of 4 pounds of
tartar emetic, 16 pounds of brown sugar and 100 gallons of wa-
ter. This is a bait spray and best results are obtained, using less

TABLE 7.-RESULTS OF FIELD EXPERIMENTS CONDUCTED AT BELLE GLADE, FLORIDA,
DURING THE SPRING OF 1940.
Quantity per 100 Mean Percent of
Spray Material Gallons Water Grade 1 Spikes
Tartar emetic 4 pounds 77.01
Brown sugar 16 pounds
Proprietary aliphatic thiocyanate 1 quart 0
Spreader 2 quarts
Calcium antimony tartrate 4 pounds 0
Brown sugar 16 pounds
Dust containing 2%aliphatic thio-
cyanate and 0.5% rotenone 0
Untreated check 0

spray material, if the spray is allowed to collect in droplets.
The spray should be applied when the first signs of injury are







The Gladiolus Thrips in Florida


observed at the base of the plant and repeated at weekly inter-
vals. Usually five to seven applications will be sufficient to pro-
tect the crop but occasionally, as in the spring of 1940, it may
become necessary to spray more often. Commercial grades of
tartar emetic can be obtained from insecticide supply houses
and at current prices its use has been found profitable. Chem-
ically pure and commercial grades of tartar emetic have been
shown to be equally safe and effective, but the latter is less ex-
pensive.

SUMMARY
The gladiolus thrips was first found in the United States
during the summer of 1929 and spread rapidly, being found in
Florida in 1932.
Injury is caused by the feeding of both larval and adult
thrips. The growing plant, florets and corms may be severely
injured when favorable conditions for thrips development occur.
A number of plants have been found to serve as hosts for
the gladiolus thrips but gladiolus is the principal host.
Several other thrips have been collected on the gladiolus.
However, none of these has been observed to cause any eco-
nomic injury.
The gladiolus thrips passes through six stages in its de-
velopment. These are the egg, first and second larval stages,
first and second pupal stages and the adult. Duration of all
stages is directly influenced by temperature and other weather
conditions. Warm, dry periods are most favorable for rapid de-
velopment of the thrips. These conditions usually occur from
February to May and it is during this period that gladiolus
thrips are most abundant in Florida. All stages of the thrips
can usually be found on growing plants during all seasons of
the year.
Unmated females lay eggs from which only male thrips de-
velop, but in nature this method of reproduction probably oc-
curs but rarely.
A few varieties of gladiolus have been found to be resistant
to thrips attack.
In other parts of the country a predacious bug and a para-
site have been observed feeding on the gladiolus thrips. In







Agricultural Experiment Station


Florida two ladybeetles were observed devouring thrips but
none of these predators is of much economic importance.
Heavy summer rains destroy large numbers of the thrips.
Thrips did not survive cold storage at 380 to 40 F. of three to
four months' duration. The corms may be treated with ethylene
dichloride-carbon tetrachloride mixture, calcium cyanide or
mercuric chloride without injury if these materials are handled
carefully. Plants growing in the field should be sprayed with
the tartar emetic bait.



OTHER THRIPS FOUND ON GLADIOLUS
By J. R. WATSON

Aside from the gladiolus thrips, the most common thrips
in gladiolus is the Florida flower thrips, Frankliniella cephalica
(Crawford). It is found in practically all blossoms in Florida and
in the gladiolus it confines its attacks chiefly to the blooms.
The adult thrips are yellow and the larvae almost colorless.
These differences in color readily distinguish it from the gladi-
olus thrips. It is not a serious pest of gladiolus cut for commercial
shipments, though it may seriously injure flowers left to open
in the garden.
The tobacco thrips, Frankliniella fusca (Hinds), is fairly com-
mon on gladiolus. This is larger than the gladiolus thrips and is
most common in gladiolus flowers in the fall of the year. By
means of a hand lens one can detect several differences between
it and the gladiolus thrips. Several of the middle segments of
the antennae are yellow. The wings are light yellowish brown
throughout. The young are a light yellow, not the deep yellow
of the young of the gladiolus thrips. They do not collect in the
folded leaves or under the bracts of the flower spikes. The adults
are often wingless, which is never the case with the gladiolus
thrips. It does not make the spots on the leaves that the gladi-
olus thrips makes (Fig. 1). This thrips, though rather common
in gladiolus flowers in the fall and winter, causes no commercial
damage. It is, however, the cause of much useless spraying by
growers who mistake it for the gladiolus thrips.
Gowdey's thrips, Haplothrips gowdeyi Franklin, sometimes
gets into the bloom. This also is a black thrips, but the ab-






The Gladiolus Thrips in Florida


domen of the female ends in a tube instead of in a saw-like ovi-
positor. This can readily be seen under a hand lens. Like the
tobacco thrips, it is of no commercial importance and its pres-
ence may be ignored.
The onion thrips, Thrips tabaci Lindn., sometimes infests
gladiolus planted near onion fields, but does little commercial
damage.
In the southern part of the state the West Indian flower
thrips, Frankliniella insularis (Franklin), may be found in gladiolus
flowers. It also is of little commercial importance. The following
key will enable one to distinguish these different species of
thrips:
A. Abdomen of female ending in a saw-like ovipositor.

B. Antennae with eight segments; part of antennae yellow
or brown.
C. Color of adult dark brown or black.
D. No long hairs on anterior angles of prothorax;
third segment of antenna differing markedly
in color from the others; young bright yellow.
-Taeniothrips simplex
DD. Anterior angles of prothorax with long hairs;
third segment of antennae not markedly
different in color from the fourth and fifth;
young nearly colorless.
E. No conspicuously long hairs on head be-
hind the eyes; adults often wingless.
-Frankliniella fusca
EE. Long hairs behind the eyes; adults nev-
er wingless. -Frankliniella insularis
CC. Color of adults yellow, tinged with orange; larvae
nearly colorless. -Frankiniella cephalica
BB. Antennae with seven segments; color, including anten-
nae, light brown. -Thrips tabaci


AA. Abdomen ending in a tube.


--Haplothrips gowedeyi







LITERATURE CITED
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555-564. 1933.
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