• TABLE OF CONTENTS
HIDE
 Title Page
 Table of Contents
 Summary
 General remarks
 Thrips tritici
 Thrips tabaci
 Enemies of thrips














Title: Strawberry thrips and the onion thrips
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Title: Strawberry thrips and the onion thrips
Physical Description: Book
Creator: Quaintance, A. L
Publisher: Florida Agricultural Experiment Station
Publication Date: 1898
Copyright Date: 1898
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Bibliographic ID: UF00024513
Volume ID: VID00001
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Holding Location: University of Florida
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Table of Contents
    Title Page
        Title Page 1
        Title Page 2
    Table of Contents
        Table of Contents
    Summary
        Page i
    General remarks
        Page 79
    Thrips tritici
        Page 80
        Page 81
        Page 82
        Page 83
        Page 84
        Page 85
        Page 86
        Page 87
        Page 88
        Page 89
        Page 90
        Page 91
        Page 92
        Page 93
        Page 94
        Page 95
        Page 96
        Page 97
        Page 98
        Page 99
        Page 100
        Page 101
        Page 102
    Thrips tabaci
        Page 103
        Page 104
        Page 105
        Page 106
        Page 107
        Page 108
        Page 109
        Page 110
        Page 111
        Page 112
        Page 113
    Enemies of thrips
        Page 114
Full Text




BULLETIN 46. JULY, 1898.


Florida Agricultnral Experimont Station.


The Strawberry Thrips
AND-
....... The Onion Thrips.


By A. L. QUAINTANCE.


The Bulletins of this Station will be sent Free to any Address
in Florida upon Application to the Director of the Ex-
periment Station, Lake City, Florida.


DELAND, FLA.
E. O. PAINTER & CO.,
1898.
















BOARD OF TRUSTEES.


HON. S. STRINGER, Presiden' ..................... Brooksville
HON. F. E. HARRIS, Chairman Executive Committee ..... (cala
HON. A. B. HAGEN, Secretary. ................... Lake City
HON. F. R. OSInORN ... ...DeLand
HON. WiM. FISHfE: ........ ... ................ Pensacola
HON. F. L. R ......... .. ... ... ......... Live Oak
HON. E. J. VANN ............................... M adison



STATION STAFF.


W F. Yocutl, A.M., D.D.......................... Director
P. H. ROLFs, M.S....... .. .....Horticulturist and Biologist
A. A. PERSONS, M.S....... ............... .. Chemist
H. E. STOCKBRIDGE, Ph.D. ................... Agriculturist
A. L. QUAINTANCE, M.S ...................... Entomologist
W. P. JERNIGAN ................. .Auditor and Book-keeper
JOHN F. MITCHELL ............. Foreman of Lake City Farm
LIRARIAN ............... ...................... Lake City
















CONTENTS.




Sum m ary ..................... .... .............. 77
General Remarks .................... ............... 79
Thrips tritici ....................................... 8o
Thrips in 1897 ................. ..... ........... 82
Experiments with Insecticides in 1897 ............... 85
Thrips in 1898 ..................... ............. 88
Life History and Habits ........................... 91
Description .................. .................. 94
Experiments with Insecticides in 1898 .............. 97
The Best Treatment ............. ............. ioo
How to Use the Rose Leaf .................. ..... Ioi
Economic Bibliography of Thrips tritici ............. 102
Thrips tabaci ....................................... 1o3
Nature of their Injury ............................. Iol
Origin and Distribution ........................... Io.
Food Plants .................... ............. 105
Life History and Habits ........................... o06
Description .................... ................. o8
Treatment ..................................... I 12
Bibliography of Thrips tritici ...................... 11.3
Enemies of Thrips ................ .............. .... 114










SUMMARY.

I. Thrips tritici:
(1) Thrips tritici has been quite destructive to strawberry and
other crops, in Florida, during the spring season of the
past two years. The damage to strawberries consists in
chafing the stigmas and ovaries, thus causing the blossom
to turn brown (blight) and eventually dry up. The
damage will be greatest during times of drouth. The
foliage of the English pea, LeConte pear and Kelsey
plum have suffered severely from the ravagesof this insect.
Various flowers are blighted, particularly certain varieties
of roses, which are frequently rendered quite worthless.
(2) The life cycle of Thrips tritici is quite short, requiring
but twelve days. Eggs are deposited in the tissues of
infested plants, and hatch in three days. The larval state
lasts for about five days, during which time the insect
makes two molts, the second when entering the nymph
stage. The nymph stage continues for about four days,
during which time they take no food, rarely move to any
extent, but remain hidden away.
(3) This insect may be successfully controlled by the use of
the Rose Leaf Insecticide, at the rate of one pint to six
gallons of water. Whale oil soap, and kerosene emulsion
may also be used with success.
II. Thrips tabaci:
(1) This insect is destructive to many plants. In Florida its
ravages have been confined principally to onions, cauli-
flower and cabbage. The leaves are chafed, which in the
case of the onion, causes the tops to whiten and dry out.
In the case of cabbage and cauliflower, the infested leaves
become browned and scorched in appearance, particularly
noticeable on the under side; leaves thus affected are of
but little functional value.
(2) The life cycle of Thrips tabaci is somewhat longer than
that of 7'-hips trifci. requiring about sixteen days for
completion. The egg state lasts about four days; the
larval stage for about eight days, and the nymph stage
for four days. The insect goes through three molts
during its life cycle.
(3) This species of thrips can be successfully controlled by
the use of the Rose Leaf Insecticide, whale oil soap, or
kerosene emulsion. They should all be used somewhat
stronger than for Thirips tritici however, as the insect
under discussion seems better able to stand them.























GENERAL REMARKS.






The name "Thrips" is applied rather indiscriminately to the
insects belonging to the order Thysanoptera (Physopoda), much
as we speak of a beetle (Coleoptera), or a fly (Diptera). The
members of the order Thysanoptera may be characterized as
follows: There are two pairs of wings, each pair somewhat simi-
lar in form, long, narrow and membranous, having but few or
no veins, and fringed with long hairs. When at rest, the wings
are placed horizontally along the back. The mouth parts are
quite different from those of any other order of insects, being
intermediate between those of biting and sucking insects. The
mandibles are reduced to bristle-like structures, while the
maxillae are flat, triangular, and hear palpi. Labial palpi also,
are present. The tarsi of thrips are composed of two joints,
without claws, each being terminated by a bladder-like structure.
The members of this order are quite small, rarely exceeding
3mm. in length; they are usually quite active, some flying readily
or leaping when disturbed, which, with their minute size has cal-
culated somewhat to keep the general public in ignorance of their
existence. All, however, are probably familiar with the small,
active insects frequently to be found in roses and other flow-











ers. This is a medium-sized thrips and will serve to illustrate
the group.
According to Dr. Heinrich Uzel, in his recent "Monogra-
phie der Ordnung Thysanoptera" the order embraces 135
species, which are distributed in thirty-five genera. Nearly all of
these are European species, but few having been described from
the United States.
The food of thrips is quite varied; some are carnivorous,
but many feed upon vegetable substances. The vegetable feed-
ers attack various portions of plants, as flowers, bark and leaves,
and in some cases they become of economic importance. It is
an interesting question as to how these insects secure foods theii
mouth parts are plainly not adapted for chewing, and but little
better for sucking. Nevertheless it seems probable that in many
cases they are used as a suction apparatus, as in Thrips tritici.
In other cases, as with Thrips tabaci, particles of leaf tissue
are torn or rasped off, and swallowed. The writer has fre-
quently seen such particles cast out with the excrement.
Probably the two species herein considered are to be
regarded as of the most economic importance of the Thysanop-
tera, in the United States; although there are several species that
cause more or less damage at times, yet the records do not show
them to be so severe nor as common as Thrips tritici and Thrips
tabaci. It should be noted that the so-called Thrips (Typhlocyba
vitifer, Fitch, and other species) of the grape vine, are not Thv-
sanoptera at all, but belong to the Jassidae, of the order Hemip-
tera. The misuse of the word thrips in this connection has occas-
ioned considerable confusion.




THRIPS TRITICI, OSBORN (FITCH).

This insect was first described in 1856 by Dr. Asa Fitch,
State Entomologist of N. Y. from specimens received from Wis-
consin. The common name of wheat thrips was given to it
from the fact that it was at that time very injurious









8i
to wheat. Dr. Fitch says, *"Although this species, like many
others in this order, occurs upon the flowers of the different
plants, it is upon wheat, in all probability, that it will be oftenest
noticed, and to which it will prove most injurious. It may there-
fore appropriately be named the Wheat thrips, Thrips tritici."
From 1856 until 1880 this insect seems not to have attracted
much attention; beginning with 1880, however, occasional refer-
ences have been made to it, as a study of the bibliography will
show. At various times it seems to have become unusually
abundant and destructive where conditions have been favorable
for its development. The insect enjoys a wide distribution over
the United States and Canada, infesting the blossoms and foliage
of various plants.
*In Florida we have this insect with us throughout almost the
entire year. In the latitude of Lake City there are short periods
of cold weather, during which the thrips doubtless hide away for
protection. But in Southern Florida they may be found more
or less abundant at almost any time of the year.
I have not been able to find any definite records of their
occurence in unusual and destructive numbers in Florida, pre-
vious to last year, except, perhaps, in Ashmead's Orange Insects,
!880, and Eubbard's Orange Insects, 1885, where mention of
thrips is made as very abundant in orange blossoms, and means
suggested for their destruction. But from these reports, nothing
very definite is gained as to their work, extent of damage, and
time of occurence. Certain it is, however, that during March,
April and May, of the past two years ('97 and '98), thrips have
occurred in myriads in various parts of Florida, and in certain
strawberry growing sections they have caused a reduction of the
usual yield of strawberries quite one-third. The strawberry crop
in Florida, particularly the early crop, is quite valuable, from the
remunerative prices it brings in northern markets, hence the
loss caused by these insects becomes very great.
The past two springs have been unusually dry, which condi-
tion seems to have been vcry favorable for the insects, and on

*Noxious Insects of New York. I and Ii. p. 307.











the other hand, has been unfavorable for plants, rendering them
less able to resist the effects of the insects. During March, April
and May of 1897, the rainfall for each respective month at Lake
City was 3.09 in., 5 in. and .66 in. The departure from the
normal was respectively, 2.50 in., 1.87 in. and 3.43 in. There
was thus a total rainfall of 8.75 in., which is 8.80 in. less than the
usual amount of rain for that period. During the same months
of 1898, the drouth at Lake City was somewhat greater than
during '97, while in many parts of the State there was practically
no rain at all. During March, April and May of '98 the rainfall
per month was respectively, 1.60 in., 1.94 in. and 1.47 in., making
the total at 5.01 in., a departure of approximately ii in. from the
normal. But aside from the amount of precipitation, the nature
of the rainfall has an important influence on the abundance of
thrips. A heavy dashing rain destroys great numbers of both
old and young, whereas a gentle, but prolonged rain causes buc
little destruction to them. Frequent examinations, several
hours after heavy rains, of plants that had been previously badly
infested, showed that but comparatively few thrips survived, at
least in the blossoms. But from the fact that the eggs are no'
thus destroyed, and from the fact that the life cycle is very short,
the thrips may soon become quite abundant again. A good
dashing rain every two weeks, would doubtless keep them so in
check, that their injuries would not be noticeable.
Thus far thrips have been unusually abundant only in the
spring, beginning with the advent of warm weather and blos-
soms, and disappearing with the approach of the rainy season in
June, or somewhat earlier.

THRIPS IN 1897.

The principal injury caused by thrips in 1897 was confined
to the strawberry. They began blighting these, in some localities,
as early as March 27th. At Lake City they were not particularly
destructive until about April Ioth, when in several fields the
bloom was observed to be becoming badly blighted. In this
locality, those fields that are on low and moist soil suffered much










the worst. For three or four weeks, some such fields did not
yield sufficient fruit to male it profitable to gather it, the clusters
of bloom browning and dying, soon after the petals were well
expanded. (See Fig. i.)
Although there seemed to be little if any doubt but that
the thrips were entirely responsible for the damage to the straw-
berry, yet the importance of proving this beyond a possible
doubt, before beginning experiments looking tcvards stopping
the trouble, made it desirable at the outset, that experiments be
conducted in this connection, and also to determine the exact
manner in which the trouble was done, and of what i' c insisted .
Hence, several Newnan plants were brought to the lal oratory,
and all blooms but unopened buds were removed. A number
of these buds were then inclosed in large glass tubes, plugged
loosely on either end with cotton. As scon as these buds hid
opened, some were supplied with thrips; others were kept unin-
fested, as checks.
The thrips at once attacked the st'gmas and distal portion -f
the styles, chafing and apparently puncturing them. In the
course of ten or twelve hours many of the stigma; began to
blacken, and twenty-four hours from this time, nearly all of the
stigmas had blackened, and the styles v.ere blackening half way
down to the ovaries, and wilting perceptibly. In the course of
another day, the styles had blackened to the ovaries and were
plainly drying up. The ovaries were also attacked and black-
ened considerably from the chafing of the thrips. By another day
the entire young fruit, receptacle, and ovaries were black and
dead, and the blackening in some cases had extended some ways
down the fruit stalk.
It should be noted that other parts of the flower were
attacked besides the pistil. The petals were sparingly attacked,
particularly at their bases; also the stamens, principally the fila-
ments. But as a whole, the preference was decidedly for the
stigmas and styles, probably on account of the sweetish sub-
stance secreted by the stigmas, to aid in the germination of the
pollen.
The blossoms in tubes not inoculated with thrips, did rot










'show this blackening and drying up. In several instances where
the stigmas were pollinated, fruit set normally.
The results seemed conclusive, yet the same experiment was
made again in the laboratory, and also in the field. In the field,
after all open and infested flowers had been removed from a
plant, it was covered with a lantern globe, by pressing bottom
end into the soil, and fastening a strip of cheese cloth over the
top. Ten plants were thus prepared. After several buds had


Fig. 1.-Illustrating on the right, a healthy Rower cluster; on the left,
one that has been destroyed by thrips. From a photograph.


opened into flowers, five plants were supplied with thrips, and
five were kept as checks. This experiment confirmed the exper-
iments made in the laboratory, and left no doubt that the thrips
were responsible for the blackening and wilting of the fruit.
The injurious effects of these insects seems to be to a con-
siderable extent in preventing the fertilization of the ovules.
Since the stigmas are attacked, and decay soon sets in, the
normal fertilization of the ovules is greatly retarded, if not
entirely prevented.








85
EXPERIMENTS WITH INSECTICIDES IN 1897.

Not much progress was made in the study of the life history
of the insect during 1897. A study of this insect is beset with
unusual difficulties, from its small size and exceeding agility.
Enough, however, was learned to indicate the most hopeful line
of treatment. Eleven different insecticides were tried, the results
of which are herewith given, as taken from Bulletin 42, of this
station.
Sulphur Spray.-Eight rows of badly infested plants were
sprayed with sulphur spray. Three rows were left unsprayed as
checks. Formula of sulphur spray used is as follows:
Flowers of Sulphur. .................... ... 3 pounds
Caustic Soda ................. ................ 2 pounds
Water ............... ....................... 1-3 gallon
To this was added two gallons of water, the whole making a
stock solution. The stock solution was used at the rate of one
and one-half pints to twelve gallons of water, and applied to all
parts of the plant with a barrel pump sprayer.
Immediately after spraying the bloom was carefully ex-
amined. A few thrips were observed to have been killed. Manx
seemed distressed, but the majority were not so severely injured
but that by the time the insecticide had dried from the blooms,
they were to all appearances about as lively as ever. The sprayed
rows were examined again the next morning when the thrips
were found as abundant as in the untreated check rows.
Flowers of Sulphur.-Four rows were thoroughly dusted
with flowers of sulphur to determine its value as a repellant. Two
rows were left as checks. No difference could be detected in the
abundance of thrips in the treated and untreated rows.
Pyrethrum Powder.-Pure pyrethrum powder was dusted
thoroughly on three rows, with a Leggett powder gun. Two
rows were left as checks. The pyrethrum seemed to be of no
appreciable value against the thrips. They were observed t)
feed readily amongst the powder adhering to the bloom.
Pyrethrum in Water.-Pyrethrum powder suspended in










'water was tried at the rate of one-fourth pound pyrethrum to six
gallons of water. This proved to be of but little if any value.
Pyrethrum Decoction.-One-fourth pound of pyrethrum
powder was steeped for an hour, the water breaking into a boil a
few times. This was diluted with eleven gallons of water and ap-
plied with a knapsack pump. Two rows were sprayed, one kept
as a check. Examination immediately after spraying showed
that a small proportion had been killed, and others were more or
less distressed. Many thrips had run out on the petals and se-
pals, from which the solution soon dried and the thrips seemed
to be unharmed. The next day no difference could be detected
in the relative abundance of thrips in the treated and untreated
rows. Doubled the strength of pyrethrum. Results, some im-
provement on above.
Tobacco Dust.-Tobacco dust was thoroughly sprinkled
over and worked among the leaves of one row of plants. One
row was kept as check. No difference in the number of insects
in the two rows could be detected, when examined at different
intervals.
Tobacco Decoction.-One pound of tobacco stems and
leaves were boiled for one-half hour in two gallons of water. This
was strained, and diluted with four gallons of water and applied
to four rows with knapsack sprayer. Two rows were kept as
check. Immediately after spraying, examination showed this
insecticide was particularly disagreeable to the thrips. A small
proportion were killed or evidently dying. Most of the adults
had left the flowers entirely. Examination the next day showed
that the sprayed plants were much freer from thrips than chcck';
Rose Leaf Insecticide.-This is an insecticide rranufactured
by the Louisville Spirit Cured Tobacco Co., Louisville, Kv. It
is claimed by the manufacturers that it is an extract of tobacco,
of a uniform strength of nicotil. It should be noted that in a
decoction made by boiling ste is and leaves in water, the per
cent. of nicotine is quite variable owing to the variation in quan-
tity of this compound i different plants. This Rose Leaf was
used at the rate of one pint to six gallons of water, and sprayed
thoroughly on five rows with a knapsack sprayer. Two rows









were reserved -as checks. Examination immediately after spray-
ing showed that the insecticide was much more effective than
anything vet tried.
Quantities of thrips were dead evidently where the spray
had first touched them. Others were dying or trying to work
their wav out of the insecticide, but were soon overcome. The
per cent. of thrips destroyed by this insecticide would probably
be near sixty-five or seventy. The action of the fluid seemed to
be that of a strong irritant, and was sufficiently sticky to prevent
the insect from escaping, after the spray had struck it.
Kerosene Emulsion.-This insecticide was made according
to the following formula:
Soap (hard) ...................................... pound
Water.......................... ................. gallon
Kerosene ....................................... 2 gallons
Two quarts of this stock solution were used to six gallons
of water and applied with a knapsack sprayer to four rows of
plants. The thrips were killed in considerable numbers. How-
ever, many that were thoroughly wet were observed to crawl out
on the hi:hecr parts of the petals, and probably eventually re-
covered. Probably a stronger solution of the emulsion would be
quite efficient, but the danger of tainting the fruit would exclude
its use. I nd the application of the emulsion of the strength
above indicated, would probably slightly taint the fruit.
Carbolic Acid in Water.-This was used at the rate of one
ounce oi acid, to six gallons of water. The acid used was com-
paratively pure, being derived from carbolic acid crystals. This
mixture was applied with a knapsack sprayer to four rows of
plants. two being kept as checks. The use of this insecticide re-
sulted in killing a small proportion of thrips and drove man,
from the blooms. Examination the next day did not show any
marked freedom of the sprayed plants from thrips, as compared
with checks.
Whale Oil Soap.-This was used in the proportion of one-
half pound :f sJap to ,ix gallonss of water. Applied thoroughly
with barrel Fump sprayer. Three rows were sprayed, one was
kept as check. This insecticide seemed to be of some value.







E8
Some insects were killed, and the flowers were comparatively
freed from thrips. Examination of sprayed rows the next day
did not reveal much reduction of thrips as compared with their
abundance in the checks.
From the results recorded above it will be observed that the
"Rose Leaf Insecticide" gave much the most satisfactory results.
Its superiority seems to be in its slight stickiness to hold sprayed
insects from escaping, and in the rapidity with which it acts upon
the insects.
It was early observed that the thrips passed readily from
plant to plant, many leaving the flowers upon slight disturbance;
and some that had been caught in the spray were able to crawl
out from the blossoms and eventually escape to other parts of the
field. This activity of the insects in passing to different plants
explains somewhat their abundance in sprayed blooms, fre-
quently in less than twenty-four hours after having been sprayed.
and comparatively freed from the insects.
To get the best results, it seems necessary that an entire
patch should be sprayed, and within as short a period of time as
practicable. To test the value of such a procedure, the entire
patch, save one row as check, upon which the foregoing exper.-
ments were conducted, was sprayed thoroughly with the "Rose
Leaf Insecticide." The results obtained from this spraying indi-
cated that much could be done to keep the thrips in check by
its use when applied to the entire patch. The thrips were reduced
throughout the patch at least one-half in numbers.

TIRIIS IN 1898.
By the last day of March, thrips were very abundant in most
flowers around Lake City, and by April 20th, they had become
even more abundant, and had attacked the foliage of various
plants, as LeCcnte pears, Kels:y plums, English peas, parsley
and endive. Their ravages were most noticeable on the foliage
of pear, plum and English pea. The tender leaves of the pear
were so rasped, usually on the under side near the margin, that
the epidermal and subjacent tissue was destroyed; from this it
resulted that the leaf soon became much curled and misshapen,
eventually browning and dying, where injured. (See Fig. 2.)
















































































Fig. 2.-Two twigs of LeCont? pear, illustrating the work of Thrifs
tritici on the tender foliage.










For about three weeks the young foliage of pear and Kelsey
plum was thus attacked, greatly retarding their growth. The
tender leaflets of the English pea were -so severely attacked that
in several fields the plants were kept quite at a stand-still for two
or three weeks; they did not recover from the attack and yielded
but a very small per cent of fruit. (See Fig. 3.)


-0


Fig. 3.-Illustrating the ravages of Thri/i trit, on the tender foliage
and flowers of the Elnglish pea.








91
The damage to the flowers of strawberries was not so severe
as in '97, but blackberries, dewberries and roses probably suf-
fered more.
In blackberries and dewberries, the damage probably con-
sists in preventing the fertilization of the ovaries, as in the case
of strawberries. There is a difference, however, to be noted, in
the result, for in the dewberry and blackberry where the fleshy
ovaries make up the fruit, a few ovaries may be left intact, and
a small and inferior fruit may result, with a few normally de-
veloped ovaries. (See Fig. 4.) In the strawberry, where the fruit

















Fig. 4.-Illustrating on the left, a normal dewberry: on the right. one
that is worthless, from the work of 7Ilri/s t itii on the stigma of the
flowers.
is made up of the receptacle, if the attack has been at all severe,
the entire young fruit dries up.
The complaint of blighting of roses has been quite general.
The petals are chafed, so that a rose soon blackens, and withers.
A bud becomes infested as soon as it is sufficiently open to allow
the entrance of the insects. In the course of eighteen to twenty
hours it is usually so blackened as to be worthless.

LIFE HISTORY AND HABITS.

To determine the life history of Thrips tritici, a considerable
number of adults were caught, divided about equally into three








9)'
lots, and placed in three bottles. In each of the e bottles, two or
three young bean pods were placed to furnish a place for ovipo-
sition, and also as food. At the end of twelve, eighteen and
twenty-four hours respectively, the thrips were removed. In the
course of about three days,the young began to work their
way out of the beans.
A just hatched thrips was carefully transferred to each of
twelve small tubes, in which had been placed a small piece of
rose petal. It was possible by this means, to keep close watch
cf each insect, and by supplying fresh food twice each day, five
of the insects were bred into the adult condition, the others
getting stuck to the tube by moisture, when very young. Four
of the thrips that reached the adult condition were observed to
go through three molts in all. The first molt occurs when the
larva is about three days old; the second, at the end of the larval
stage, when the nymph stage is entered; this occurs about five
days after hatching. The nymph state lasts four days, when the
final molt into the adult occurs.
From the above it is seen that the egg state lasts approxi-
mately three days, the* first larval stage for three days, the
second for two days, and the nymph stage four days, making a
total of approximately twelve days for the life cycle. The same
experiment was made again, about two weeks later, with practi-
cally the same results. The larval stage was found to vary some-
what, in one case it lasted for nearly seven days. The number
of molts was found to be the same as previously recorded.
Oviposition was observed but once. In this case the thrips
was on the outside of the calyx of a rose; the ovipositor was
gradually worked down into the tissue, quite its length, and after
a few seconds pause, the abdomen was seen to be contracting
and expanding; five or six contractions occurred, when after a
sudden movement of the antennae, the ovipositor was suddenly
withdrawn, and the thrips ran on. Careful dissection of the
calyx revealed the egg. its apex almost level with the epidermis
In strawberries, eggs are placed mainly in the calyx, on the
outside, where it surrounds the base of the large receptacle; as
many as eight eggs have been found here, in a badly infested








flower, by peeling back the epidermis, to which the eggs will
remain attached. Many eggs are placed in the flower stalk,
sometimes as far as three inches below the flower. In rare cases,
eggs are placed in the bases of stamens, but never in the pistil,
so far as I have observed. In the bean, eggs are deposited
almost entirely in the flower stalk, the apex just even with the
surface. In roses, eggs are placed in about the same position as
in the strawberry, that is, in the calyx on the outside, and less
usually in the flower stalk.
In hatching, the young thrips gradually works out until
about four-fifths up, when the antennae and legs become separ-
ated from the body, and falling forward, it soon pulls itself free,
the whole process requiring not more than one-half hour. As
soon as hatched, the insect possesses considerable agility, and by
three or four hours has taken sufficient food, that it may be
detected in the alimentary canal, through the white semi-trans-
parent body. In the course of eighteen hours they attain the
characteristic bright orange-yellow color, though not yet so deep
as in an older larva. In feeding gregariously, they make defensive
use of the strong spines on the end of the abdomen, by striking
right and left at the intruder, and usually securing a wider berth.
Some eight or ten hours before molting into the nymph state.
a thrips retires to a secluded place, where it remains very quiet,
and unless molested, rarely moves. It gradually loses its bright
yellow color, and eventually molts. The nymph stage is passed
in a secluded place, frequently where the molt occurred. In
tubes, the space between the small end of the cork and tube was
a favorite place, or a dried petal was used. Unless disturbed,
the nymph rarely moves; when disturbed, its movements are rath-
er slow and uncertain, particularly in an older nymph. When this
stage is first entered, the wing-pads are quite short, rarely reach-
ing the caudal margin of the second abdominal segment, by the
end of the first six 'or eight hours. At the end of about thirtv-
six hours, the pads are of full length, that is, reaching to near
the end of the sixth abdominal segment. During the latter
part of this stage, the skin and body seem to separate, somewhat,
so that they may be clearly distinguished. When just molted,









the adult is light yellowish, and does not attain its normal color
until some hours later.
Adult thrips are quite agile, readily flying when disturbed,
or at other times. A florist recently reported to me, that he had
iecen very much annoyed by their crawling over his face and
hands, and biting, as he sat by an open window in a lighted
room at night. From personal experience, I know that they are
capable of producing an unpleasant sensation of biting, when
on the hands. They fly around some extent, at least, through
the day, as I have frequently ol served them on my clothing,
some distance from their food pla.ts.

DESCRIPTION.

Egg.-Size, .25x.Imm (.oo9x.oo3 in.); clear whitish in colo-;
oblong, curved in shape. (See Fig. 5, Plate I.)
LARVA, FIRST STAGE.-Length about .5mm, (.ol9 in.),
width of thorax nearly .Imm. (.003 in.); body fusiform, gradually
tapering caudad from fifth or sixth abdominal segment.
Color, clear whitish; eyes, reddish. Antennae distinctly four
jointed: basal joint, cylindrical, short; second somewhat urn-
shaped, with distinct distal rim, about as long as broad; third
joint conical, apex of cone united to second; fourth, fusiform,
widest near basal fourth, quite as long as other three joints
together. Joints two, three and four ringed; two and three
rather obscurely, but on fourth joint the rings are quite pro-
nounced, where, on distal part, they appear,to divide the joint
into short cylindrical segments. On the fourth joint the rings
are minutely state. Numerous large setae also are present on
all joints, most numerous on fourth. Legs stout; hind femur
about as long as tibia; tarsus one-jointed, terminating in claw-
like fork; bladder-like expansion of adults apparently wanting.
Abdomen composed of ten segments, marked dorsally with four
longitudinal rows of setae, and a row on each side. All of these
setae appear to be somewhat enlarged and rounded distally,
except one pair on dorsum of last segment. On tenth segment
these setae are quite long, being from two to four times longer
than the others. (See Fig. 6, Plate I.)







95
PLATE I.


/


Fig. 5.


Fig. 7.


Fig. 9.


Fig. e Fig. 6.
Tlriys tritici.--. egg; d. larva. first stage; 7, mature larva. second stage; .8
nymph. or 1upu; 9. adult female. All figures except 9, drawn by Mr. .T P. Davies,
under Ihe author's direction. Fig. 9, from a photomicrograph. All much enlarged.









L.\RVA, SECOND STAGE.-Length about 1. mm. (.039 in.):
width of thorax about .22 mm. (.008 in.); shape about as in Stage
i. Color of body, deep orange yellow; legs and antennae lighter;
eyes reddish; antennae four-jointed as in first stage; basal joint
short, cylindrical, about one-half as long as wide; second, sub-
cylindrical somewhat longer than wide; third sub-conical about
a third longer than wide; fourth about as long as proximal three
together, fusiform, thickest about basal fourth. Joints three
and four plainly ringed, the rings of fourth joint quite distinct
and minutely state as in first stage. Large setae also are
present about as in Stage I. Femur of hind legs about as long
as tibia; tarsus one-jointed, somewhat forked distally, and bear-
ing a mebraneous expansion. (See Fig. 7, Plate I.)


NYMPH OR PUPA.

(I) YOUNG NYMPH.-The young nymph has a general
resemblance to an adult larva in shape; in color it is much
lighter, being light yellow, with legs, antennae and wing-pads still
lighter. Eyes reddish.
In the antennae, legs and wing-pads the nymph skin appears
somewhat as a sheath to these parts of the forming adult. The an-
tennae are three or four jointed apparently, thick and clumsy. The
basal joint is large, swollen, slightly longer than wide; the second
is about twice as long as wide and somewhat constricted in mid-
dle. Third joint is about a third longer than second, gradually
tapering distally to an obtuse end. When the nymph stage is first
entered the antennae project cephalad, in normal position. In
six or eight hours, however, they are laid back over the head
and prothorax. The mouth parts are rudimentary, and are
plainly not adapted to procuring food during this stage. In the
hind legs, femur and tibia of about equal length; tarsus indistinct-
ly one-jointed, very short and rounded distally. Wing-pads short,
scarcely reaching caudal end of second abdominal segment, bear-
ing one or two setae. Abdomen as in larva, with dorsal and lateral
rows of setae, which, however, are acute. On the dorsum of










ninth segment, near caudal margin, are four stubby, hook-like
processes, curving cephalad, which appear to be the four modi-
fied setae for this region.
(2) MATURE NYMPH.-Length about I mm. (.039 in.);
width of thorax about .22 mm. (.008); color light yellow; shape
very similar to that of adult thrips. Nymph skin more or less
separated from body of the, adult within, particularly so in the
legs, antennae, mouth parts, wing-pads and caudal end of abdo-
men. The wing-pads reach to about the sixth segment. The
mature nymph is, of course, but the adult encased in the nympi
skin. (See Fig. 8, Plate I.)
ADULT.-"Male, length, .75-.80 mm. (.029-.o3I of an inch);
width .20 mm. (.007 of an inch). Female, length, 1.10-1.20 mm.
(.042-.046 of an inch); width .25 mm. (.009 of an inch). Color,
yellow, thorax tinted with orange; antennae with dusky annula-
tions. Head from above nearly square, eyes occupying anterior
angles. Antennae approximate at base, joint two, apical half
of four, and six, dusky; joints three and five dusky at apex, the
antennae appearing annulated under low power of microscope.
Head, thorax and abdomen with a few stiff hairs. Legs con-
colorous with body, all the tibiae with two spines at the distal
end, distal joints of tarsi a little dusky, proximal joints of tarsi
with two spines. Wings narrow, hyaline, fringes whitish;
anterior wings have a costal fringe of shorter ciliae than pos-
terior ones, and the ciliae are intermixed with shorter, stiffer,
spiny hairs, which at base replace the fringe; two rows of black-
ish spines on the upper surface of wing corresponding with sub-
costal and mediam veins.
Posterior wings with no discal spines, ciliae of anterior edge
shorter and more spiny than those of posterior. Both wings
have rows of very minute hairs on the surface. The males are
shorter and smaller than the females, with wings reaching be-
yond the tip of the abdomen."-H. Osborn. (See Fig. 9, Plate I.)

EXPERIMENTS WITH INSECTICIDES IN 1898.

It was intended to conduct extensive experiments against
the thrips, to further perfect a remedy, and to find other and








98
cheaper insecticides than those tried during '97. With the co-
operation of Prof. Rolfs, a series of comparative tests of different
insecticides was undertaken in the laboratory, as a preliminary to
further field work. But before field work could be undertaken,
the thrips had become so reduced in numbers that it did nx
seem profitable to undertake the work. The results of the labor-
;to; v tests are, however, given. As thrips were needed, a num-
ber of wide mouthed, four ounce bottles were taken to the field.
n.nd a considerable quantity of them collected in each, by picking
off several blackberry blooms, shaking them in the bottle, and
suddenly throwing out the flowers, after which it was corked.
Thrips thus collected were brought to the laboratory, and as
each was sprayed with a particular insecticide, another bottle of
exactly sane kind was tied to it, with the mouths together. The
sprayed bottle was then closely wrapped in a black cloth, and the
unsprayed bottles turned towards the light; by this means it was
thought that thrips not destroyed would the sooner make their
way to the unsprayed bottle, where, after separation of bottles,
the per cent. of those alive and killed could be more easily de-
termined.
The following substances were tried, being applied with a
hand antomizer:
No. 1. Rose Leaf Insecticide.-(a) i part Rose Leaf to 32
parts water. Result, all dead, about 175.
(b) I part Rose Leaf to 64 parts water. Result, all dead,
about 200.
No. 2. Whale Oil Soap, Anchor Brand.-(a) I part soap to
96 parts water. Result, all dead, about 200.
(b) I part soap to 192 parts water. Result, dead, about 12o;
alive, 5.
(c) I part soap to 240 parts water. Result, dead, 175; alive, 5.
No. 3. Kerosene Emulsion.-Formula:
Soap (hard) ...................................... i pound
W ater ..................... ... ................ i gallon
K erosene ............ .......... .. ...... ....... 2 gallon
Diluted with 16 parts water. Result, all dead, about 50.









99
No. 4. Sulphur Spray.-Formula:
Flowers of Sulphur .............................. 3 pounds
Caustic soda ................... ............... 2 pounds
WV after ....................... ............... I-3gallor
To this was added 2 gallons of water, the whole making a stock
solution, which was used at the rate of I part sulphur spray to
30 parts water. Result, dead, 64; alive, 39.
No. 5. Pyrethrum Powder.-About 75 were shaken up in
a bottle with a half teaspoonful Pyrethrum. None were ob-
served in second bottle, after a lapse of twenty-four hours.
No. 6. Pyr.ethrum Decoction.-One ounce powder to one
quart water, boiled 20 minutes. Dead, 44; alive, 38.
No. 7. Tobacco Decoction.-(a) Tobacco stems and leaves,
2 ounces: I quart water, boiled one-half hour. Dead, 149;
alive, 6.
(b) I part decoction to 32 parts water. Result, dead, 175;
alive, 3.
No. 8. Tobacco Decoction and Syrup.-Tobacco, 2 ounce;;
water, I quart; syrup, 4 ounces. Result, dead, 80; alive, 30.
No. 9. Bluestone (CuSO:).-Bluestone, I ounce; water. 8
ounces. Result, dead, 107; alive, 94.
No. o1. Salsoda (Na2CO3).-Salsoda, I ounce; water, 8
ounces. Result, dead, 127: alive, 49.
No. II. Powell's Kerosene Emulsion.-I pound to Io gal-
lons water. Result, dead, 71; alive, 70.
No. 12. Water.-Sprayed thoroughly with water. Result,
dead, 3; alive, 75.
No. 13. Hammond's Thrip Juice, No. 2.-(a) Used at rate
of I to 20 parts water. Result, all dead, about 175. (b) I to 40.
Result, all dead, about 200oo.
No. 14. Potassium Sulphide (K2S).-(a) I to 64. Result,
dead, 200; alive 70. (b) I to 256. Result, dead, 30; alive, 45.
No. 16. Common Salt (NaCI).-I to 6. Result, dead, 129;
alive, 14.
No. 16. Potassium nitrate (KNO3).-I to 8. Result, dead,
178; alive, 68.
In addition to these, tobacco smoke and sulphur fumes
were tried in the field. Both were applied with a Crane bee










smoker, to badly infested bean plants. The tobacco smok2
quickly stupified the insects, but in most cases they eventually
recovered.
Sulphur fumes did not seem to have much effect on them.


T"iE IHEST TREATMENT.

Reviewing the experiments thus far made in the field, it will
be observed that the Rose Leaf Insecticide gave much the best
results. The insects died in most cases when fairly struck by the:
spray. In the laboratory experiments in 1898, it- will be notice:f
that several insecticides were very efficient when the thrips were
bottled up. By the use of the following insecticides, all of the
insects treated were killed:
Rose Leaf Insecticide, I to 64; Whale Oil Soap (Anchor
Brand), I to 200; Kerosene Emulsion, I to 16; Pyrethrum Pow-
der, undiluted; Hammond's Thrip Juice, I to 40.
But it does not necessarily follow that these insecticides
would be as efficient in the field. Thus, the Whale Oil Soap
used in the field experiments last year, did not compare favora--
blv with results obtained from the use of Rose Leaf, while in the
laboratory the restuls were identical. It should be noted, how-
ever, that different brands of soap were used in field and labora-
tory experiments; in the former, a low grade was used, and in the
latter, Leggett's Anchor Brand.
And again, by the use of Pyrethrum in the laboratory.
all thrips were killed, while in the field, it had little if any effect.
-This difference in results is doubtess due to the use of pyrethrum,
in the one case in a bottle, where the odor is confined, and in
the other, in the open air, where its value would be greatly
lessened.
In addition to spraying, particularly in the case of strawber-
ries and roses, it would be of much value to carefully remove all
blighted flowers, with their flower stalks and quickly throw them
in kerosene or burn them. By doing this, numerous thrips and
the eggs in the calyces and flower stalks would be destroyed,









IOI
which would materially affect the abundance of the insects in the
future.
Spraying should be repeated as the abundance of the insects
demands. Whenever the thrips become so abundant as to be de-
structive to any kind of plant, they are usually quite abundant in
many other plants also, and a field of strawberries, for instance,
that has been quite freed from them by spraying, might, in the
course of ten or twelve days, become badly infested again.
Hammond's Thrip Juice, No. 2 in the laboratory, proved
very efficient. Field experiments are yet necessary to de
termine if it will be equally effective there. It
is believed that by' the use of Rose Leaf Insecticide,
Whale Oil Soap (Anchor Brand) or Kerosene Emulsion, thrips
can be kept greatly reduced, and their ravages minified to a
considerable extent.
The use of Kerosene and Whale Oil Soap, however, can
hardly be recommended for the treatment of thrips in strawberry
fields from which ripe fruit is being picked, from the fact that
the fruit would be more or less tainted by the oils of these insecti-
cides. In other cases where no fruit would be sprayed that is
to be immediately used, their use would probably prove quite
satisfactory. The Rose Leaf, on the other hand, does not injure
fruit for immediate use, as it washes off readily, hence everything
considered, cost, ease of preparation, range of application and
effectiveness, the Rose Leaf Insecticide is recommended in
preference to anything that we have yet tried.

HOW TO USE THE ROSE LEAF.

Simply mix it with water at the rate of one pint to six
gallons, and apply it thoroughly to infested plants, with a spray
pump that gives a fine and forcible spray.
It may be purchased of the manufacturer for 75 cents per
gallon, of stock solution; a gallon diluted with the prop r
amount of water, would make forty-eight gallons of the spraying
mixture, costing I and 6-Io cts. per gallon. This is approximately
the cost per gallon of Kerosene Emulsion, ready for use, not










including the cost of its preparation; and somewhat more than
the cost of a gallon of Whale Oil Soap solution. It is hoped
that a cheaper insecticide may yet be found.

ECONOMIC BIBLIOGRAPHY OF THRIPS TRITICI.

Ashmead, W. H.:
Orange Insects, 1880. p. 72;
Insect Life, VII, 1894. p. 27; (on cotton).
Brunner, L.:
Insect Enemies of Small Grain, Rept. Neb. St. Bd.
Agrl. 1893. p. 457;
Insect Enemies of the Apple in Neb., Neb. St. Hort. Rept.
1894. pp. 163., 214.
Fitch, Dr. Asa:
Ist-2nd Repts. Ins. N. Y., pp. 304-308.
Count. Gent. VI, Dec. 13, 1855. p. 385.
Fcrbes, S. A.:
I6th Rept. Ins. Ill. 1890. p. IX. pl. V;
17th Rept. Ins. Ill. 1891, pp. XIII. XV.
Thrips or Strawberry Midget. (Thrips tritici), Centralia.
Ill. Sentinel 1887; Reprint, Prairie Farmer, june 4,
1887; Insect Life, V. 1892. pp. 126-127.
Hubbard, H. G.:
Insects Affecting the Orange 1885. pp. 164-165. (U. S.
Dep. Agrl).
Lintner, J. A.:
Thrips in Strawberry Blossoms, Cultivator and Country
Gentleman, V. 52, 1887, June 9, p. 459;
Some Literature of the Thripidae, IIth Rept. N. Y. State
Ent. pp. 247-250.
(Osborn .:
The Canadian Entomologist, Aug. 1883, pp. 151-156.
Insect Life, I, 1888, p. 141;
Insects of the Orchard, Bull. Iowa Agrl.. College, Aug.
1884. No. 2. Trans-Iowa State Hort. Society, 1883-
84. V. 18.











Powers. S.:
Strawberries and Pears, (Editorial) Florida Farmer and
Fruit Grower, Mch. 27, 1897.
Riley, C. V., Howard, L. O.:
Insect Life, I, 1889. p. 340.
Rolfs, P. H.:
Florida State Horticultural Society, 1897 p. 97.
Townsend, C. H. Tyler:
Canadian Entomologist. 24. Aug. 1897. p. 197.
Webster, F. M.:
Ohio Exp. Station Bulletin No. 45, 1892., pp. 207-208.
Weed, C. M.:
The Strawberry Midget, Prairie Farmer, 59, 1887, p. 343;
Trans. Ill. State Hort. Society. 1887, pp. 230-233;
Popular Gardening, 3, 1888, p. 176.
Insects and Insecticides, 1895, p. 146.



THRIPS TABACr LIND.*

During the spring seasons of the last two years, this species
of thrips also has been quite destructive at Lake City, injuring
onions, cauliflower and cabbage. The conditions favorable for
Thrips tritici seem also to have been favorable for its near rela-
tive. It has varied considerably in abundance during the spring,
at times becoming much reduced, and again it would be present
in great numbers. The insect was first noticed about the middle
of April in 1897, when it was observed to be infesting
onions on the Station gardens. The insects were destructive
until about July I, when they gradually disappeared.
In 1898, the insect was observed, April 28th, to be quite
abundant on onions in the Horticultural department, and some
'days later, Prof. Rolfs called my attention to its occurence on
cabbage and cauliflower. To these plants it proved quite

*I am under obligations to Dr. L. O. Howard for the deter
mination of Thrips tabaci.










104
destructive during May, and the first two weeks of June. By the
last of June, the insects were becoming very scarce, and at this
date (July 15th) none are to be found. Beginning with July,
considerable rain has fallen, which may have hastened their dis-
appearance.

NATURE OF THEIR INJURY.

This species is injurious to the foliage of plants. On the
onions, it chafes off the epidermis from the green leaves, there-
by causing them to drv out, whiten and frequently die. On the
cabbage and cauliflower their effects are about the same. They
are much more abundant on the lower surface of the leaves.
where they chafe off the leaf substance, much as in their attack
on onions. The leaves of cabbage and cauliflower, however, par-
ticularly on the lower side, become brown, and have a scalded
appearance. Such leaves eventually become much dried up, and
doubtless are not of much functional value.

ORIGIN AND DISTRIBUTION.

This insect has even a wider range than Thrips tritici; ac-
cording to Mr. Th. Pergande, Assist. Entomologist, U. S. Dep.
Agrl., it occurs in the following localities: Russia, Germany,
Bermuda, Connecticut, New York, New Jersey, Pennsylvania.
Virginia, Ohio, Illinois, Colorado and California. To these
should now be added Florida. It is doubtless of European origin,
and has been brought over in some shipment of onions or cab-
bage. The' insect was first made known to science, by Dr.
Lindeman, of Moscow, who found it very destructive to tobacco,
in Southern Russia. At Lake City, although occurring in cab-
bage fields adjacent to tobacco fields, it has not been observed to
attack tobacco.
The extent of its work in other States may be judged from
the following quotation from Lintner's IIth Rept. as State Ento-
mologist to N. Y., p. 244: "This species has been commonly
recorded as depredating on the tops of onions, and its injuries
have been quite serious at times, as in the instance reported by








135
Dr. Packard, where in 1872, one-tenth of the crops of Essex Co.,
Mass., was destroyed by it at an estimated loss of $1o,boo. In
some localities, it has proved so destructive that the growing of
the srop had been abandoned. Next to onions, its preference
seems to be for cabbage. It might be thought that this was a
recently acquired taste, for during the space of twenty years no
record appears of its being found upon this plant-the first such
publication being that made by me in 1892, in the Country Gen-
tleman, as above cited. It seems that, however, Mr. Pergande
has found it recorded in his notes, as occurring in the District
of Columbia and Virginia, during the years 1882 to 1888, on the
leaves of cabbages. In 1894, its operations on cabbage were
studied by Messrs. Sirine and Lowe, of the New York Experi-
ment Station on Long Island. It was not very harmful to the
cabbage, as it attacked and killed mainly the outer leaves, and
deserted them the latter part of September for onion fields."

FOOD PLANTS.

The following list of food plants is also taken from the same


source:
Cabbage.
Kale.
Cauliflower.
Turnip.
Candy-tuft (Iberis).
Mignonette (Rescda ordorata).
Nasturtium (Tropacolum).
Blanket-flower (Gaillardia).
Cone-flower (Rudbeckia).
Catnip (Ncpcta cataria).
Heal-all (Brunclla vulgaris).
Four o'clock (Mirabilis).
Sweet Clover (Mclilotus alba).


Cinquefoil (Potcntilla).
Stonecrop-? (Scdum).
Squash.
Cucumber.
Melons.
Parsley (Carum sativum).
Tomato (Lycopersicum esculen-
ltmi).
Tobacco (,'icotianra tabccumin).
Jamestown weed (Datura stramr
niium).
Garden leek (Allium porrum).
Onion.


To this list should be added Crab-grass (Panicum sanguin-
alc, L.) on the leaves of which the insects were collected, May
15th, 1897, at Lake City.








io6
LIFE HISTORY AND HABITS.

According to Dr. Lindeman,* who has studied the life his-
tory of this insect in Russia, the eggs are elliptical, of a reddish
color, measuring not more than .25 mm. in length, and are glued
along the smaller veins of the leaf, on the lower surface. This
stage was found to last ten days. Larvae hatched July loth in
large numbers feeding on the leaves, until August ioth, when
they suddenly disappeared, and were found to have gone to the
stalk and upper side of the leaves, where they passed the nymph
stage. On indirect evidence the nymph stage is given as seven
days. Thus the life cycle requires forty-seven days. Three
generations were observed during the year.
Mv own observation on this insect during the past spring in
Florida, do not agree with those of Dr. Lindeman. The insect
was studied, on onions, cabbage and cauliflower, their behavior
being practically the same on the three plants. As many as ten
insects were bred through all stages, and numerous tubes of
thrips were studied with respect to various points.
The eggs were deposited singly, just beneath the epidermis
of the plant infested.**
In the onion this may be anywhere on the leaf. In the case
of cabbage or cauliflower a slight preference is shown for the
veinlets.
The process of oviposition was observed but once. In this
case the egg wasplaced in a cauliflower leaf in about the same way
as with Thrips tritici but with this difference: previous to cutting
a slit in the leaf with the ovipostior, a small patch of epidermis wa.


*Die Schadlichstcn Insekten des Tabak in Bessarabien-pp.
56-59. (Moscow, 18b6.)
:*In bulletin 27, of the Iowa Agricultural College, p. 13),
l'rof. ()sborn states that the eggs of Thrips alii, Gillette (Thrips
tabaci, Lind.) are deposited slightly beneath the surface of the
leaf, and imbedded in the cell structure. (The observation is
credited to Miss Alice M. l'each.)








107
torn off with the mouth parts. The thrips then advanced, and
worked the ovipositor down in this exposed place. Further ob-
servation of course is necessary to determine if this is a usual
habit, or was accidental in the instance observed.
The egg of this species is almost colorless, elongate, and
curved, very similar indeed to those of Thrips tritici. The egg
state lasts from three and a half to four days. Upon hatching,
the larvae are quite agile, running about readily if disturbed.
They are almost transparent in color but become gradually of a
greenish yellow color, the greenish tint due doubtless to the con-
tained food. These larvae are somewhat gregarious in their
habits, and may be seen feeding together in groups. Like Thrips
tritici they also use the spines on the end of the abdomen to
drive away intruders, by striking right and left. In almost all
cases it has the desired effect, and the victim seems glad to get
away. The larval stage lasts from seven to nine days, during
which time the insect goes through two molts. The first occurs
from two to three days from birth, the last, being into the
nymph stage. The nymph stage lasts for four days, the insect
remaining almost in the same tracks throughout the period, if
left undisturbed. No food is taken.
The wing-pads for the first few hours.are short, hardly
reaching the caudal margin of the second abdominal segment.
In two days, however, they are full length, reaching to near the
eighth segment. Some four to six hours before molting into the
nymph, a larva, in tube bred specimens, leaves the food and
retires to as protected a place as possible, where it remains
quietly, and gradually becomes somewhat lighter in color. Dur-
ing the nymphal stage these insects move with difficulty, and are
plainly at considerable disadvantage. Nymphs were found in
some abundance in the field, in onion fields they were found
almost entirely down on the bulb, in the loose soil. In the case
of cabbage and cauliflowers, they were found hid away in the
dead leaves, and in the pits in the leaf scars. Nymphs, however,
could not be found in anything like proportionate numbers to
the adults and larvae, and it seems probable.that the usual place
for passing this stage was not found.








io8
The third and last molt of the insect is from the nymph to
the adult condition. A newly developed adult is quite light in
color, and does not acquire the normal color for twelve to fifteen
hours. The length of life of an adult was not satisfactorily deter-
mined. Specimens were kept however for nearly three days, when
they met with an accident.
From the above it will be seen that the total life cycle of
the insect in Florida is approximately sixteen days, a difference
of about thirty-one days, from that of its.life cycle, in Russia, ai
recorded by Dr. Lindeman. In Russia three distinct broods
may occur yearly. In Florida, there are probably no distinct
broods, as all stages may be found at the same time. Allowing
for the life cycle at sixteen days a large number of broods could
occur during the year, but unfavorable conditions keep them
reduced, except during the spring and perhaps early summer,
so that it will probably not happen that they will develop
throughout a year, according to their capabilities.



DESCRIPTION.



EGG.-Length, .26 mm. (.oi in.); width, .12 mm. (.004 in.);
in shape the egg is elliptical and curved. Fresh eggs are
clear white. In eggs with advanced embryos, the reddish eyes
are distinctly visible.
LARVA, FIRSTr STAGE.-(About one-half hour after hatching)
Length, .38 mm. (.014 in.); width of thorax, .14 mm. (.oo5 in.),
somewhat fusiform in shape, gradually tapering caudad from
fourth or fifth abdominal segment; body, legs and antennae, clear
white; eyes reddish. Head in dorsal aspect, about as broad as
long; the eyes are situated on the cephalic lateral margins; no
ocelli. In cephalic aspect the head is seen to be considerably
produced ventrad and caudad, sub-oval in outline. The four-
jointed antennae are born from the vertex, and are approximate










at base. The basal joint is short, cylindrical, of about one-hali
the length of second; second joint sub-pyriform, slightly longer
than wide; third, sub-spherical, about as long as second. The
fourth joint is as long as the proximal four together, club shaped,
thickest near the basal third, from where it gradually tapers dis-
tally to a point. Joints three and four are ringed; in the distal
part of joint four, these are much more pronounced, dividing
it into what might be taken for short, indistinct segments. The
antennae bear setae which are much more numerous on fourth
joint. Legs stout; coxae and trochanters short; femur about as
long as tibia and tarsus together. The tarsus appears to be
composed of but one joint, which terminates distally in two
diverging claw-like processes; the bladder-like expansion on tip
of tarsts does not seem to be present in this stage. The abdo-
men is composed of ten segments; on the dorsum of abdomen
are four longitudinal rows of acute setae, and a row also on each
lateral margin. On the tenth segment these setae are quite large.
being from two to four times longer than the others.
MATURE LARVA (Second stage).-Length, .94 mm. (.036
in.); width of mesofhorax .22 mm. (.oo8 in.). Body elongate,
abdomen tapering caudad from about fifth segment. Head
slightly longer than wide. Color greenish yellow, varying to
greenish white. Legs and antennae lighter; eyes reddish brown;
ocelli wanting. Setae practically as in stage I. Antennae four-
jointed;* basal joint short, cylindrical; second sub-cylindrical,
about twice as long as first. Third joint a fourth longer than
second, sub-pyriform, united to second by narrow "neck,"
rather closely ringed. Fourth, about as long as proximal three



*Lindeman regards the antennae as six-jointed, but to me,
joint f6ur has not appeared, to allow 'of being considered as
made up of three joints; although there are four more or less
well defined parts as determined by the ring,', which, if con-
sidered as joints, would make seven in all, instead of six.










together, club-shaped, ringed as in stage I. Antennae bearing
setae, much more numerous on fourth joint. Tarsi without the
pronounced claw-like structures of first stage. In other respects
essentially as in the preceding stage. (See Fig. io.)
NYMPII (about two days
old).-Length, about .7 mm.
(.027 in.); width of mestho- .
rax, about .15 mm. (.005 in.); *
color, yellowish, varying to
almost colorless,- eyes red-
dish. Pupa-skin somewhat
separated from the body
proper, being particularly no- ,
ticeable in the caudal end of
the abdomen, wing-pads, legs
and antennae. In these two -'. r
latter, the joints are very ob-
scure, the pupa-skin covering
them as a sheath. "
The wing-pads reach to
about the eighth abdominal
segment. There are numer-
ous setae on the anten- Fig. lO.-Mature larva of Thrifs ta-
ous setae on the body, anten- ,i. from a photomicrograph, much
nae, legs and wing-pads. On enlarged.
the abdomen they have p-actically the same position as in the
adult larva. The dorsal setae, of the last segment in the nymph,
are very stout, almost hook-like, cuving cephalad. (See Fig.II.)
ADULT.-The adult Thrips tabaci is I mm. long, or some-
what longer, pale yellow, eyes and tip of snout (Russelspitz)
black. The caudal margin of the abdominal rings, black in the
middle. Body with few short hairs, which on the last two seg-
ments appear somewhat longer; upper surface of the body with-
out spines; on the vertex of the head are three small ocelli.
Forehead, between the closely placed antennae, with no tooth-
like process. Antennae seven-jointed. Joint one, thick, cylin-
drical; two, barrel shaped, somewhat longer than one, indis-









III
tinctly ringed; joints three, four, five and six, elongate, elliptical,
of almost equal length, except joint six. which is somewhat
.,. longer. All are indis-
-' .tinctlv ringed. Joint
seven, small, cone
shaped, a little more
Than one-half shorter
Than the preceding
S. joint. Legs simple,
thigh not inflated,
.* wings colorless, reach-
ing the caudal margin
S. of the sixth abdominal
S segment. Their upper
surface finely haired.
The fore-wing with
2 veins; hind-wing
fr- with hut one vein. The
"caudal margin of the
Swings bear long, dark,
wavy hairs, which ex-
tend merely as far as
he middle of the mar-
gin. The cephalic mar-
Fig. 11. -Nymph of Thrips tabaci. from a iholotomi
crograph, much enlarged. (In figures 11 and 12 the gin bears short, spine-
spines and setae are somewhat abnormal. ona like hairs.
count of an over zealous retoucher.)
The abdomen of the female consists of ten segments. The
two last taper gradually without forming a tube-like ending.
The ovipositor, when projecting out, free, is seen to consist of
four sword shaped, yellow plates with serrated margins. The
receptaculum seminis is situated in the sixth abdominal seg-
ment, appearing as a brown pear-shaped vesicle.
The males are smaller than the females. Their abdomen is
only nine segmented. In the sixth and seventh abdominal seg-
ments lies a pair of brown spoon shaped chitinous plates of un-










known function. At the caudal end of the abdomen is the
nipple like copulatory organ, whose end bears two colorless
hooks, and which is covered from below, by a half-round plate,
the ninth segment."- From Lindeman's Die Schadlichsten [nsek-
ten des Tabak in Bessarabien, p. 63. (See Fig. 12.)


Fig. 12-Adult Th/ri tabaci. from a photomicrograph, much enlarged.


TREATMENT.

Several insecticides were tried against this insect. They
may be successfully controlled by the use of Whale Oil Soap
(Anchor Brand), at the rate of one pound of soap to four gallons
of water; or by the use of Rose Leaf Insecticide, at the rate of
one pint to four gallons of water. The use of Kerosene Emul-
sion will also be found effective.
In spraying against the insect, it should be done thoroughly;
the soil around the plant should also be sprayed as well as the
stems of cabbages and cauliflowers, thus destroying the pupae
that may be in hiding.


: i
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113
BIBLIOGRAPHY OF THRIPS TABACI.

Limothrips tritici, Flitch. Packard: 2nd Ann. Rept, Ins. Mass.,
1872, pp. 5-8, 3 figs. (Erroneous reference.)
Thrips on Onions Plants, Shipley: In Bull. io Miscellaneous In-
formation, Royal Gardens, 1887. p. 18.
Thrips tabaci, Lindeman: Schadl. Ins. d. Tabak in Bessarabien,
1888, pp. 51-65 (life history, habits, description, remedies).
Thrips sp. Thaxter: in Ann. Rept. Conn. Agr. Expt. Stat., 1889,
p. 180 (injuries in Conn.).
Thrips sp. Riley-Howard: Insect Life, III, 1891, p. 301 (refer-
ence); id., VI, 1893, pp. 4-5 (reference).
Thrips sp. Coquillett: in Insect Life, IV, 1891 p. 79, (seriously
injuring potatoes and tumble weed).
Thrips tabaci, Lind. Ritzema Bros.: Tierische Schadlinge und
Nutzlinge, 1891, pp. 577-578, (description, brief notice).
Thrips sp. Lintner: in Count. Gent., Oct. 27, 1892, Ivii, p. 809,
(on cabbage); 9th Rept. Ins. N. Y. for 1892, 1893, p. 445,
(abstract of notice in Count. Gent.).
Limnothrips sp. Baker: in American Florist, 1892, vii, p. 168, fig.
occurringg in rose buds)..
Thrips striata, Osborn. Gillette: in Bull. 24 Col. Agrl. Expt.
Stat., July, 1893, p. 13, figs. II,-12, (may be n. sp., and sug-
gests allii.); in 5th Ann. Rept. Col. Agr. Expt. Stat. for 1892,
1894, p. 36; in 6th do. for 1893, 1894, p. 55 (referred with
doubt).
Onion Thrips. Smith: in Ann. Rept. N. J. Agr. Coll. Expt. Stat.
for 1893, 1894, p. 441; in id. for 1894, 1895, p. 447 (abun-
dant); Econom. Entomol., 1896, p. 102 (mention).
Thrips allii, Gillette. Sirrine: in Bull. 83, New Ser., N. Y.,
Agr. Expt. Stat., 1894, pp. 680-683, plate ii; the same in
13th Ann. Rept. N. Y. Agr. Expt. Stat., for 1894, 1895, pp.
758-760, plate.

*The Bibliography is taken from Lintner's I th Report, as
State Ento. to N. Y., pp. 241-242.









Thrips allii, Gillette. ()sborn-Malley: 111ll. 27. Ia. Agr.
Coll. Expt. Stat., 1895, Pp. 139-142.
Thrips tabaci, Lind., Pergande: in Insect Life, 1895 vii, pp. 392-
395 (general account).
Limnothrips tritici, Pack. Webster: in Blull. 58 Ohio Agr. Expt.
Stat., 1895, pp. xxxiii-xxxiv (on onions in Ohio).
Thrips tabaci, Slingerland: in Rural New Yorker, Iv, 1896, p.
561 (at Peace Dale, R. I.; brief notice with remedies).
To this bibliography should be added:
Thrips tabaci, Lind. Targ. Tozzetti: Animali ed Insetti del To-
bacco in Erbal del Tobacco Secco, 1891, pp. 222-224,

ENEMIES OF THRIPS.

Probably the most serious insect enemy of thrips is the
Triphleps insidiosus, Say. This insect is very common in
flowers infested with thrips and has frequently been observed -u
thrust its beak into thrips larvae and suck from them their body
substance. Both the larvae and adults are predacious on the two
species of thrips here considered. The eggs of this Triphleps
are placed in the tissues of plants with those of the thrips. In
tw3 cases, bean flower stalks were put in tubes to breed out
thrips from the contained eggs. In these flower stalks were eggs
of the Triphleps also, which hatched, the young feeding on the
young thrips; these (about fifteen in number, in one case), were
quite destroyed by two Triphleps before the thrips had attained
the adult larval condition. The life cycle of the Triphleps is
quite short, requiring but about fifteen days.
The larva of a species of Chrysopa was occasionally ob-
served feeding on thrips larvae, which were caught by the long
mandibles, and sucked after the usual manner of these insects.
During the spring of 1897, a nematode worm was occasion-
ally pressed from the abdomen of thrips, though it is by no
means certain that these were parasitic. Both eggs and adults
were to be found at the same time, in one individual.


A. L. QUAINTANCE.




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