DEVELOPMENT

O'viposition.

— ^{As may}

^beinferred

^{from what}

^{has been said of the}

sexual apparatus of the

two

suborders, each has its

own method

^oft

oviposition.

The

Terebrantian femalecuts aslitwithher

saw

throughⁱ the epidermisand deposits her eggssingly in thetissueof the plant.

The

process of oviposition is as follows in AnaphothrijJS strlatusand!

willdoubtlesshold in

most

points for the group:

The abdomen

is raised

somewhat

and the ovipositor is let

down from

the sheath till it is nearly ai right angles to the Ijody.

The

^•

abdomen

isarched tobring theweight of the

body

to l)ear

upon

the slendersaw, the valves of which are then

moved

back and forth

upon

each other

by

j)owerfulmuscles in the ninth segment.

The

toothed^I blades are gradualh^

worked down somewhat

oliliquelyinto the tissue,

and when

the slit issufficiently largethere

may

be seen successivecon- tractions of the

abdomen

as the

Qgg

^is

pushed

out betweenthe valves- of the ovipositor and under the epidermistill it is nearly concealed.

The

entireoperation requires about oneand a halfminutes, and

upom

its completion the female

moves

^off a short distance to rest or feed.

Occasionally the ovipositor

becomes

so firmly

wedged

in the plantas to hold its possessor prisoner for

some

time, frequently until deathⁱ results _(469).

I feelsure thatThr'ips'perpleoc/iisand Chirothripsobesus willbe found todeposittheir eggs externally.

The number

of eggslaid

by

a single female has been observed only^>

in the case of Anaphothrlps driatns,

from

^{a numl>er of}

which

an averageof

from

50 to 60

was

obtained, the

maximum

average from a lot of 5 females being 72. These observations

were made

in the laboratory

upon

females confined in bottles.

The

percentage of eggs which hatched

was

also observed in this species

and was

found to

varyin thelaboratorj^

from

35 to 40 percent. Itseemsveryprobable that the artificial conditions under

which

these experiments were

made must

have in this case greatly reduced the percentage ^that hatched

below

the normal.

HO.1310.

NORTH AMERICAN TIIYSANOPTERA—

HINDS.

113

Tubulifera deposittheireggs externally, either singly or in groups,

upon

leavesandllower.s or underbark, etc.,according to theirhabitat

The

period of oviposition inall species in this orderis quite long.

^W-— ^The

^{eggs of} Terebrantia are

more

or less elongated and slightly bean-shaped.

They

arecolorless, delicatein structure, and no micropyleisapparent.

The

position oftheeggs ina thin leafiseasily seen

upon

holding the leaf before a l)rightlight,

when

they appear as brighter spots in thedarker greentissueof the leaf.

Eggs

are laid in almost

any

green part of theplant, butnot in thepetals offlowers.

The

eggs ofTubulifera are of an elongate-oval shape, attached with the long axis perpendicularto the surface, and haveatthefree

end

a thickening of the chorion with amicropyle in the middle.

The

eggs vary

from

3'ellow to brownish in color.

Fm7)/-i/oIof/y.—

The

development of the

embryo

can be observedin the translucenteggsof Terebrantia. Various writers agree in stating thatthe

germ band

is innnersed. Beforerevolution the appendagesof the

embryo

lie alongthe convexsideof the egg,after revolutionalong the concaveside.

The

length of the

egg

stagevaries considerably in different species and, even _{within the}

same

species, according tothe weather conditions.

So

far as life histories are

known,

this stage appearstolast

from

three tofifteen daysin Terebrantia, but no record

isfound

upon

this point for the Tubulifera.

The

pigmented eyes of de^•eloping

embryos

are particularly prominent. If the

egg

bed dries the

egg

is quickly destroyed, but if moist, even though decaying, the

j

development _continues.

Fnicnjence

of

^the

/arm.— When

readytoemerge, the

young

Tere- brantian lan^a breaks through the tender chorion and pu.shes

up

through the slit in the epidermis

made

for the insertion of the egg.

The

larva

works

its

way up

tillall but thetip of the

abdomen

isfree, but remains supported

by

the tip in this upright position until the antenna and legs haveseparated

from

the body, to which they areat first closely applied,and have

become

sufficiently dried and hardened ioruse. It then falls forward onto its feet and is readyto travel or to feed almost immediately.

No

observations have been found onthis point for the Tubulifera, but just as theireggs are laid singly or in groups, so alsodo

we

findthelarvte.

Larval stage.—Thelength of the larvalstagevarieswith thespecies, andthe statementsrecorded place itat

from

fiveto forty days.

When

just hatchedthehead of the larva is very large'in proportion to the

body and

the

mouth

parts areessentially like those of the adult.

The

thoracic segments are subequal.

The abdomen

is strongly con- tracted

and

veryrough.

As

the larva

grows

the thorax and

abdomen

enlargenoticeably, while the head

shows

littlechange. In

some

spe- pies{IIeIiofknj)s) the

abdomen

becomesstrongly distendedand shining

3.S though under considerable pressure, and a globule of fluid excre- Proc. N.

M.

vol.

xxvi—

⁰² 8

114 PROCEEDINGS OF THE NATIONAL MUSEUM.

^xxvi.

ment

is frequently held

by

thehairs around the anus.

The

larva?are lessactivethan theadults and have no

power

of springing.

The

lar- val antenna always ^has fewer segments ^than the adult. In Phlreo- thripidffi the

number

is constantly seven. Thickened femora andtar- sal hooks do not occur, the tarsus appears tobe one segmented, and claws

may

or

may

not bepresent.

The

structure of the foot is nuu-h

more

^{distinctthan intheadult.}

The

eyes are not

compound,

l)ut com- posedof a

few

separated facets,

which

are strongly elevated and always circularin outline.

The number

of facets increasesinsuccessivemolts, but the circular

form

^{is retained.}

The

rudiuients of the ovipositor or genital apparatus appear on the under side of the eighth and ninth segments as indistinct lobes.

The

foodhabits of the larvtv are just as variedas are those^of theadults, and

some

species arealso found

upon

theroots of plants.

J/<>/?'.v.

— From two

to fourmoltsappear to occur while in the larval

stage, the last

marking

thechange^to thepupa.

The

chitinous cover- ing of the internal

mouth

parts and of the bladders can be distinctly seen in the cast skin.

When

larvw have

become

^full

grown

they cease to feed,

become

restless, and seek

some

very secluded place ⁱⁿ which to molt. In this search they are so successful that in

many

species pupee are hardto find.

Nijnqyh ^nr Pupa.

— The

metamorphosis of Thysanopterais peculiar, for

though

complete in

many

^{respects, it is}

nmch

^{less so in others.}

Two

stages are distinguishable while ⁱⁿ the

nymph

^{condition. After}

thelast larvalmolt, the insect still retains its larvalappearance, the antennie are extended,

and

the

pro-nymph

ismoderately active.

The wing

pads are partially developed, extending ^{to al)out the second} abdominal segment,

and

the beginning of the formation of theadult appendages ^can be seen. After anothermolt, the true

nymph

stageis

reached and the animal remains quiet unless disturbed,

when

it is

capable of slight

movement. No

food is taken during this ]5eriod.

The

antenna? are laid

back upon

the head

and

prothorax; ^{their seg-} mentation has

become

^indistinct

and

the adult antenna can be seen within the

nymphal

skin.

The

numl)er ^{of facets inthe eyes greatly} increases, producing the adult condition.

The

logs are inclosed ⁱⁿ loose sheaths and the

wing

pads reach to and

from

the sixth to the eighth segments.

The

pads extend ^obliquely

outward

alongthe sides of^the

body and

do not cover each other.

The

fringes appear along the edges of theforming wings, the fore fringebeing directed^to\vard the tip

and

hind fringe toward the base of the wing.

The

forming lobes representing the ovipositor^elongate, and thoseoneach side over- lap l)ut remain separate.

Within them

develop the pointed valves ^of the adult ovipositor,

which now

^{extends to ,tho tip of the abdomen.}

The

development of the malegenital apparatus takes place in a very similar

way

^{to that}of the ovipositor ^ofthe female.

The nymph

^stage

NO.1310.

NOR TH A MERICAN THYSA NOPTERA—HINDS. ₁₁₅

ispassed in

some

secluded place,

pup*

being found in the loose soil

; aboutthe base of theplant, in the leaf sheath, or

some

similarlypro- tected place,

and many

have been recorded as transforming in galls.

.When

thesechanges have beencompleted, another molttakes placeand theadult emerges.

The

most noteworthy points in the metamorphosis

may

be

summa-

rized as follows:

The

larvareseml)les the adult ingeneral

form

and in

mouth

parts; wings aredeveloped inexternal sheaths; the transitional stage between larva and adult is quiet, and duringit no nourishment

is taken.

The

metamorphosis istherefore intermediate between com- pleteand incomplete.

//^7v6'r;?«?'/o//.—Thysanopterapass the winter in either_larval, pupal,

ior adultstages.

Many

species,withoutdoubt, hibernateinvery nearly the

same

places in which they have fed.

The

bark-inhabiting forms remain in such places, together with

many

of the leaf forms' which migrate ontothe trunk.

The

dried stems of flowers and grassesshel- ter

many

species, while

many

of the leaf-inhabiting forms fall to the

ground

and are

among

thosewhich

may

be found underfallen foliage, in moss, etc. Lichens and fungi shelter

some

as winterguests, while [deadgrass and turf contain

many

forms. It appears very probable that

some

of the larvae

which

have been found

upon

the roots of plants

were

hibernating there rather than feeding thereon,as hasbeen supposed.

I

The

hibernating individuals appear to be able to withstandextreme degrees ofcold and moisture. I have broughtin a

number

of species gathered bypulling_the frozen grass

from

bare

mowings

in midwinter after a temperature of

-21-

F.

Upon

being l^rought into a

warm

room, they very soon

became

active and ran about.

' Thrips

emerge from

hibernation very early in the spring, and as

^oonas their normal food plants begin to

grow most

of

them

are in a condition todeposit eggsfor a

new

generation, which in

some

cases in Massachusetts hatchduringthelatter part ofApril orthetirstof

May.

' Length

of Ufe.~YQ\f

observations have been recorded

upon

this point, but it seems improbable that even the longest lived exceeda ,mgle year.

Among

those species which produce several generations n a season, the hibernating individuals

must

live for atleast seven nonths inthe northern United States while the summei- generations ire

nmch

shorter lived. Their age however, as a rule, considerabl3\

exceeds the length of the life cycle, for oviposition is a slow_process, ind in Ana2)hothr{2Js striatm is

known

to extend over a period of

^ve or sixweeks.

As

a result of this there is an indistinguislia))le )verlapping of broods. I have kept a female of a

midsummer

gen- eration of.1. striatusconfined in a bottle in the laboratory for almost Ive weeks. This species has eight or nine generations in u season.

:nd

may

therefore be expected to be one of the shortest lived in

ummer.