THE OVIPOSITOR OF HYMENOPTERA

96 SMITHSONIAN MISCELLANEOUS

VII. THE OVIPOSITOR OF HYMENOPTERA

The

ovipositorof theHymenoptera,regardless of the shape,length, or function

assumed

by the shaft of the organ, has the

same

basic structure throughoutthe order. Initsgeneral

form

andinthecom- position of the shaft thehymenopterousovipositor resemblestheovi- positor of the

Hemiptera more

closely thanthat of the Orthoptera, butithasoneparticularfeature,namely,thearticulationof thesecond valvifersonthefirstvalvifers,insteadofonthe ninthtergum,which

is a characteristic feature of the ovipositor of Gryllidae, though the

mechanism

isnot exactly the

same

inthe

two

cases.

The

salientpoints inthe structure of the hymenopterousovipositor

may

besummarized as follows

:

1.

The

subgenital plateof the femaleis the seventh sternum,and the base of the ovipositoriscontainedina vestibularcavity.

2.

The

eighthterguminlowerfamiliesisa dorsalplateof the usual form exposed externally; in the bees it is entirelyconcealed within the seventh segment, its median part is reduced to a

membranous

foldovertheback,

and

thelateralparts

form

a pair of smallsclerites bearing the eighth spiracles.

3.

The

eighthsternumiscompletelysuppressedinallHymenoptera, though the venter of the eighth segment

may

be represented by a fold of

membrane

beneaththe gonopore.

4.

The

firstvalvifersareentirelydissociated

from

theother parts of theeighthsegment and

form

anintimate part of the basal

mechanism

of the ovipositor or sting. Theirmuscles, however,take their origin on the eighthtergum.

Each

is a small triangularplate bearing the

ramus

of the first valvula on its anterior end, and articulating pos- teriorlybyits dorsal angle with the ninthtergum,and byits ventral anglewith thesecondvalvifer.

89

5.

The

ninth tergum is complete in lower families, its widened lateral partsbeing continuous dorsally at least ina narrow sclerotic bridge,withwhich the proctiger

may

be united^;inthebees the ninth tergumconsists of

two

largelateral sclerites,

known

as the^"quadrate plates^",but the medianpart of the ninth

dorsum

is

membranous

and notdistinct

from

theproctiger.

6.

The

second valvifers are oblong plates bearing anteriorly the ramiof thesecondvalvulae,andposteriorly the third valvulae.

Each

isarticulatedbyits dorsalmargin with the ventral posterior angle of the firstvalvifer (not with the ninthtergum), and is provided with the usual anteriorandposteriormusclesarisingon the ninthtergum.

7.

The

venter of the ninth segmentis always

membranous,

there beingnointervalvularsclerites.

8.

The

shaft of the ovipositor or sting is

composed

of the first

and second valvulae, the first beingventral, the second dorsal.

The

secondvalvulae are united with each other beyond their convergent rami, either solidly or by

membrane,

and

two

pairs of muscles are inserted ontheirbases,onepair arisingontheproximalparts of the rami, the other on the inner faces of the second valvifers. These muscles of the second valvulae are characteristic features in the

mechanism

of the ovipositor or sting of the Hymenoptera, but they appearto have no homologues in other insects.

9.

The

^third valvulae are free lobes ensheathing the distal part of the shaft of the ovipositor; theyvarygreatlyin lengthaccording tothelength of theovipositor.

10.

The

proctiger isalwayspresent. Inlower families it consists ofa dorsalanda ventralplate,andbears a pair of small appendicular processes^;inthe higher families^itbecomes reducedtoa simple

mem-

branous tube or cone.

Four

examples,selected

from

theTenthredinidae, Braconidae, Ich- neumonidae, and Apidae, will serve to illustrate the characteristic structureand

some

of the principal modifications of the ovipositor as theorgan is developed in the Hymenoptera.

PTERONIDEA

RIBESII (sCOPOLl)

The

relativelylarge

abdomen

of thefemalecurrant sawfly contains theusual loabdominal segments present in the Hymenoptera.

The

eight pairs of spiracles are located in the lower parts of thetergal plates.

The

first segmentisbroadly joinedtothethorax;itstergum

is divided dorsallyby a median

membranous

area,andthe precostal regionformsanarrowpostnotal plateof themetathorax;the venter of thefirstsegmentis reduced andcontainsno sternal sclerite.

NO. 8 INSECT

ABDOMEN

SNODGRASS I07

The

seventhsegment formsthelastcompletelyexposed annulus^of theabdomen. Its tergum (fig. 35A,

VIIT)

resembles the terga of the preceding segments, but the sternum

(VI

IS) is extended as a subgenital platebeneath thebase of the ovipositor, and ends in two small lobesembracingthe ventral valvulae.

Above

theseventhsternum

isa vestibularcavity, in the anterior wall of which isthe gonopore.

The

eighth

tergum (VIIIT)

has the

same

shape asthe seventh,but its lower ends are overlapped by ^the posterior lateral angles of the seventh sternum.

The

venter of the eighth segment is represented onlybythe

membranous

integument formingthe anterior wall of the vestibulumcontaining thegenitalaperture.

The

ninthtergum

(IXT)

is narroweddorsally, butis expanded on thesidesof the ninth seg- ment, where its lower marginsoverlap the secondvalvifers {2Vlf).

Between

the valvifers the

membranous

venter of the ninth segment formsadeepconcavityinwhichislodgedtheshaftof theovipositor.

The abdomen

terminateswitha conical proctiger (Ptgr) bearing ven- trolaterally apairof slender processes (Soc). Beneaththe proctiger the third valvulae (3VI) project as a pair of short, broad, dark- coloredlobes,normally embracingthetipof the ovipositor{Ovp).

The

ovipositorof Pteronidearibesiiisrather weak,since the eggs of the currant sawfly are deposited on the surface of the leaves of the food plant, but ithas the characteristic

form

of the

sav^y

ovi- positor.

The

shaft of the organ is

composed

of the broad, laterally compressedfirstand secondvalvulae (fig.35^{B, iVl,} 2VI), whichare respectively ventral

and

dorsal to eachother.

The

dorsalblades are united for theirentire lengthby a

narrow

median

membrane

(E).

The

outer surface of the distal part of each valvulaiscrossed

by

a series of strong, oblique ridges (C,

D)

; the

membranous

proximal partistraversedbyanarrowflexible

ramus

{C,rivl,E,r2vl) which curves

upward

tothe basalattachment of eachvalvulawith the cor- responding valvifer.

The

firstvalviferis a small triangularscleritelying anteriorto the lower end of the ninthtergum (fig. 35B, iVlf),

where

it ismostly concealed beneath the lower part of the eighth

tergum

(A). It is definitely articulated by its dorsal posterior angle (B, C, a) to the ventralanteriorangle of the ninthtergum,and byitsventralangle (&) tothe dorsaledgeof thesecondvalvifer.

The ramus

of thefirstval- vula is continuous with the first valvifer at the anterior angle of thelatter (c).

The

secondvalvifer is a large elongateplate (fig. 35^{B, E,}2Vlf) lyingbeneaththeeighth

and

ninth terga

(A)

. It isconnectedby

mem-

brane with the ninth tergum,but has noarticulation withthelatter,

its fulcrum of

movement

being thearticulation withthelowerangle of thefirstvalvifer (B,b).

The

wide

membranous

proximalpart of the second valvula is broadly unitedwiththe ventral margin of the anterior part of thesecond valvifer (E),butits

ramus

{rsvl) isat- tached to the anterior angle of the valvifer. Posteriorly the second valvifer bears the short, broad thirdvalvula (A.B, E,3VI).

Fig.35.

—

Abdomen and ovipositorof Ptcronidca rihcsii (Tenthredinidae).

A, endofabdomenwith ovipositor innaturalposition.

B, ninth segment,with proctiger andovipositor.

C, leftfirstvalviferand^{firstvalvula.}

D, distalpartofsecondvalvula.

E, left second valvifer and second and third valvulae, with united ends of second zmlvnlac turnedoutward showinglongramus (rJvl) unitedwith second valvifer.

a,articulation of first valvifer with ninth tergum; b, articulation of first valvifer with second valvifer; c, attachment of ramus of firstvalvula to first valvifer;e,attachmentofmusclefromeighthtergum onfirstvalvifer.

The

basal

mechanism

of the tenthredinid ovipositor brings about anopposite

movement

of the dorsalandventralvalvulaebytheinter- actionof the

two

valvifersoneachother, andof thefirstvalviferon theninthtergum.

A

dorsal rotation of the anteriorendofthesecond valviferonthe lowerpoint of thefirstvalvifer causes a rotation of thefirstvalvifer onthe ninthtergum,and vice versa, withtheresult thatthefirstand secondvalvulae aresimultaneously

moved

inopposite directions.

NO. 8 INSECT

ABDOMEN

SNODGRASS IO9

The

proctiger of the lower

Hymenoptera

is of particular interest because of the pair of appendicular processes arising

from

it. In Pteronideatheproctigerconsistsofabonnetlike dorsalplate(fig.35 B, Ptgr) and of abroad, flat,

membranous

ventral flap, which enclose theanus

(An)

betweentheir distalends.

The

appendicular processes (Soc) are attachedtothemarginofthelower endsof the dorsalplate of the proctiger.

The

writer has been unable to find any trace of muscles connected withtheseappendages, though a large muscleex- tendsintothe proctiger

from

the ninthsegmentdorsaltothe base of each process.

The

proctiger of the

Hymenoptera

isprobablya

compound

segment containing the tenthandeleventh abdominalsomites,thoughthere is littleevidenceeveninthe larvae of the presence of the eleventh somite.

Ithasbeen

shown

by Nelson (1918), however,^thatinthe

embryo and young

larvaof thehoneybee thereisevidence of1 1abdominalganglia.

The

newly hatched larvahas nine distinctganglionic masses in the nerve cordof theabdomen,thelastofwhichliesinthe caudal region behindthe eighthsegment, and contains three pairs ofnerve centers,

making

thus atotalof 11 pairsof gangHoniccentersintheabdomen, which is indicative of the presence of the

same number

of somites.

In the maturelarva the composite endganglion has unitedwith the ganglion of the eighth somiteto

form

thedefinitiveterminal ganglion of the adult.

The

appendagesof the proctigerhaveusuallybeen regardedas the cerci. If,however,

we

accept the embryological evidencethat cerciare theappendagesof the eleventhabdominal segment,itisdifficulttosee

how

these appendicular processes of the proctiger in adult

Hymen-

optera can be cerci, since in larval stages of the

same

insects the eleventhsegmentisabsent,or represented onlybythecircumanallobes of the terminalsegment.

The

postpedes, or terminal appendages, of sawfly larvaeclearly belongto the tenth abdominal segment, as do those of lepidopterouslarvae,

and

itisclaimedby Middleton (1921) that these larval appendages of Pteronidea ribesii give rise to pro- tuberances of the tenth segment in the

pupa

within which the pro- cessesofthe proctiger of the adult are developed.

Though

Middleton callstheadult processes "cerci"_his

own

evidence suggests thatthey are identical in originwiththe appendages of the tenth segmentof thelarvaandare, therefore,not truecerci.

The same

argumentap- plies to the appendicular processes of the proctiger present in adult males of

some

Lepidoptera, termedthe sociiby lepidopterists.

The

sociievidently are notcerci, sincethe eleventhabdominalsegmentis

suppressed in the caterpillars and the last appendages in both the

no SMITHSONIAN MISCELLANEOUS

COLLECTIONS VOL. ©9

larvaandthe

embryo

arethose of the tenth segment. Hence,^itseems probable that the proctiger of adult Lepidopteraand

Hymenoptera

is

mostly the tenth segment of the abdomen, and thatits appendicular processes, if they represent segmental appendages at all, are the appendages of the tenth segment. Likewise the processes of the proctiger in adult male Trichoptera appearto behomologuesof the socii of Lepidoptera,andhere again the terminal appendages of the larvabelongtothe tenth abdominal segment.

The

^{writer, therefore,}

tentativelydesignates theappendagesofthe proctigerinTrichoptera, Lepidoptera, and

Hymenoptera

the socii, since clearly it is

more

probable that they represent thepygopods,orappendagesof the tenth segment,presentinthelarvae,thanthatthey are thecerci,orappend- ages of the eleventh segment, which segment is suppressed in the larvae ofallthese insects.

On

the other hand, the terminal appendicular processes of the ab-

domen

of adultMecoptera and Diptera

may

be truecerci. In

Panorpa

theyarise

from

a small butdistinct endpieceof the

abdomen

beyond the tenthsegment, whichbears theanusonitsventral surface,andis therefore the eleventh segment.

The

morphology of the terminal appendagesofMecopteraand Dipteraisdiscussedina recentpaperby Gerry (1932),

who

regards the structures as cerci.

ATANYCOLUS

RUGOSIVENTRIS

(aSHMEAd)

The

ovipositor of this

member

of the Braconidae will illustrate the structure of theslender,elongatetype of ovipositorcharacteristic of

many

of the parasiticHymenoptera.

The

functional

abdomen

of a braconid, as that ofall the higher families of the order, contains only nine segments, since thefirstabdominalsegment formsthe pro-

podeum

of the thorax,andthereisbutonepostgenital segment,which

istheproctiger.

The abdomen

of Atanycolusrugosiventris (fig. 36

A)

iselongate oval, rather broad, and of a pale orangecolor contrasting with the blackish thorax, head,andlegs,andtheduskywings.

The

tergaand sterna of thevisceralregion are separatedby widelateral

membranous

areas, andthe tergal platesof segments

HI and IV

are fused.

The

slender shaft of the ovipositor

(Ovp)

isnearly as longasthe

abdomen

and

thorax,andthe third valvulae {3 VI) are correspondingly length- ened

and

narrow. In life the third valvulae probably ensheath the ovipositorbetween^theirhollowedinner surfaces.

The

seventh,eighth, andninthtergal plates of the

abdomen

are narrowed above (B) and separatedby wide intersegmental membranes.

The

seventh sternum

(VIIS)

projects posteriorly beneath thebase of the ovipositor as a

NO. 8 INSECT

ABDOMEN

SNODGRASS ^III large subgenital^plate.

There

isnoeighthsternum, andthe venter of the eighthsegment^isrepresented onlybythe

membrane

of the anterior wall of thevestibulum beneath^thegonopore.

The

proctiger {Ptgr) contains a dorsal and a ventral plate,and bears laterally a pair of small appendicular processes ^(socii).

The

shaft of the ovipositor and the third valvulae project

from

above the seventh sternum (fig. 36 B).

The

dorsal second valvulae

Fig. 36.—Abdomen^andovipositorofAtanycolnsrngosivcnlris (Braconidae).

A, abdomen,with ovipositor separatedfromthe ensheathing third^valvulae.

b',endofabdomenandbaseof ovipositor.

C, distalpartof shaft of ovipositor. . • 1 -j

D, ventral viewofbase ofunited second valvulae, with ramus ofright side showingunion with secondvalvifer.

E, base ofovipositorandninth tergum,showingarticulation of firstvalvifer ata'with ninth tergum,andatbwith secondvalvula.

are solidly united with each other in the free part of the ovipositor (D, 2VI), and the tip of the resulting median dorsal piece of the shaft is

somewhat

enlarged and slightly decurved (C).

The

^first

valvulae slide freely on the ventral margins of the secondvalvulae, andtheir distalends (C) are strongly serrate on their loweredges.

The

^basal

ramus

of eachfirstvalvula (E, rivl) curves

upward

andpos- teriorly to its attachment (c) withthe dorsal margin of the corres-

SMITHSONIAN MISCELLANEOUS

COLLECTIONS VOL. 89 pondingfirstvalvifer (iVlf).

The

proximal endsof theunitedsecond valvulae (D,E,2VI)present

two

lateralswellingswhichabut against the anterior ends of the second valvifers, but

from

each a

narrow ramus

(D,r2vl) curves

upward

andposteriorly against the inner face of the

ramus

of the firstvalvula of the

same

side,

and

is broadly attachedtoaproximaldorsal lobe of thesecondvalvifer {2Vlf).

The

firstvalviferisasmallplate (fig.36E,iVlf) articulating be- tween the anterior ventral angle of the ninth tergum (a) and the dorsalmargin of thesecondvalvifer (&)^;itgives attachmenttothe

ramus

of thefirstvalvula (rivl)byitsuppermargin (c).

The

lateral partof the ninth

tergum (IXT)

has the

form

ofa sclerotic fold,the outer wall of which is deeply emarginate where the wide interseg- mental

membrane

behind the eighth tergum is attached to it.

The

second valvifer is a large, elongate plate (fig. 36E, 2Vlf), overlappedbythelowerangle of the ninthtergum,but,asinPteron- ideaandotherHymenoptera, having noarticulation or specificpoint of

movement

onthelatter;itrocksonthe ventral pivot (&) of the^first valvifer.

The

anterior end of the second valvifer is expanded in a dorsal lobe

(D)

to whichthe

ramus

of the secondvalvula (r2vl) is attached. Posteriorly thesecondvalviferbears thelong,slenderthird valvula (E,3VI).

The mechanism

of the braconidovipositor is the

same

as that of Pferonidea.