The Morphology and Functions of the Reproductive Systemsof Dendroctonus monticolae' Hopk. (Coleoptera : Scolytidae)-

By H. F. CERIZKEForest Entomology and Pathology Laboratory, Calgary, Alberta

Abstract Caned. Ent. 96: 477-500 (1964)The male and female reproductive organs of the mountain pine beetle,

Dendroctonus monticolae Hopk. arc described, and interpretations given for func-tions of the parts on the basis of activity during mating, sperm transfer, egg for-mation and ovulation. Some morphological changes of the reproductive organsduring the adult life cycle are also noted.

Three pairs of accessory glands associated with spermatophore production areevident in the male beetle. One of these was previously termed the seminalvesicles. A complex musculature operates the male genital organ during copu-lation. The female organs have four telotrophic ovarioles with a posterior calyxregion that has a possible secretory function. Evidence indicates that organs pre-viously termed "colleterial glands" have a digestive and reabsorbing function. Thebursa copulatrix may be more closely allied with the function of the accessoryglands than with the mating process. Parts of the spermatheca have been moreprecisely defined according to function.

IntroductionThe mountain pine beetle, Dendroctonus monticolae Hopk., has been the

object of much investigation during the past 60 years, but few studies relatingmorphology to functional anatomy have been attempted (e.g. Hopkins 1909;Richmond 1935; and Reid 1 958a, I962b). Reproductive organs of North Ameri-can bark beetles have generally been described to provide taxonomic information.European contributions provide more information in the field of comparativemorphology (e.g. Stein 1847; Escherich 1894; Niisslin 191 1-1 2; Heberdey 1931;and Chararas 1956).

The reproductive organs of D. monticolae were described briefly by Rich-mond (1935). Some of the important changes that take place in the organs ofthe adult female were shown by Rcid (1958a, 1962). Reid (1958b) also des-cribed the mating behaviour and other activities associated with fecundity. Thepresent study was carried out during 1960-62 and describes the male and femalereproductive systems from both a morphological and functional viewpoint. Theterminology has been augmented and clarified in sonic instances. Much of thisinformation may be applicable to other scolytids.

Materials and MethodsThe mountain pine beetles were obtained from naturally infested lodgepole

pine (Pious contort,: Dougl. var. latifolia Engelm.) near In yermere, British Colum-bia. Two rearing techniques were employed for obtaining reproductive struc-tures in the desired stages of development and for observing adult behaviour withinthe egg gallery. In the first method broods of the mountain pine beetle werereared on freshly cut logs of lodgepole pine. Unmated tenerals, unmated andmated females in the egg-laying condition and adults in the flight stage were thus

ISince this paper was submitted for publication D. monticolae and D. jeffreyi have been synonymized withD. ponderosae (Wood, S. L. 1983. A revision of the bark beetle genus Dendroctonus Erichson (Coleoptera:Scolytidae). Gr. Basin Nat. 23: 1-117).

2Contribution No. 993, Forest Entomology and Pathology Branch, Department of Forestry, Ottawa, Canada;from a thesis submitted to the Faculty of Graduate Studies, University of Alberta, Edmonton, in partial ful-filment of the requirements for the degree of Master of Science, 1962.

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478 THE CANADIAN ENTOMOLOGIST March 1964

obtained. Secondly, observation plates (Reid 1962b) were made by sealingsheets of inner bark of pine between plates of transparent Lucite. A male andfemale beetle were introduced into each plate and their mating, gallery elongationand egg-laying behaviour observed. This technique permitted the selection ofadults during specific periods of behaviour. Most rearings were carried out atroom temperature.

Reproductive organs were fixed in either formal saline or alcoholic Bouinfixatives and were embedded in Tissuemat (m.p. 60-62 C.). Sections were cut at6-8 p, stained with Delafield's hematoxvlin and counterstained with eosin (Daven-port 1960). Mating pairs were fixed b y brief immersion in boiling formal salineand whole mounts were prepared of genital structures.

Drawings were made to scale using a calibrated micrometer eyepiece and acamera lucida. The terminology of the reproductive parts was obtained fromseveral sources including Hopkins (1915), Richmond (1935), Snodgrass (1935),Francke-Grosmann (1948, 1950) and Lindroth and Palinen (1956).

Results and DiscussionGeneral Features of the Adetathorax and Abdomen

The combined abdomen (Abd) and metathorax (Metath) is roughl y cylindri-cal and tapered sharply posteriorly. There are only minor external morphologi-cal differences between the sexes in these two regions. According to Imms (1957)the abdomen is cr yptogastrous, consisting of terga (T) I to VIII and sterna (S)III to VW (Fig. 1). Sternites I and II are apparentl y fused to sternite III and•are concealed within the hind coxal cavities (Richmond 1935). No externalaccessory structures arc associated with the posterior segments. The segmentsthat are associated with sexual differences and with attachment of the reproductiveorgans are described below.

Tergite VII is a prominent sclerite in both sexes (Richmond 1935) and carriesan externally visible sex character. Two stridulators scrapers project fromthe posterior point of this sclerite in the male. The sound produced by thesescrapers provides a convenient method of separating the sexes of living beetles.

The tergite of the eighth segment is more conspicuous in the male; in thefemale it is covered to a greater extent by the seventh tergite than in the male. Inboth sexes the eighth sternite is much reduced and is entirely concealed b y theeighth tergite and seventh sternite except briefl y during mating and egg-laying.

Scicrotization of the eighth sternite in the male is greater laterally than medi-ally (Figs. 4, 10). In the female the median portion is entirely membranous (Fig.18). The lateral thickened portions of this sternite serve as points of attachmentfor musculature that extends ventrally to the seventh sternite (Fig. 19). Thesemuscles allow telescopic movement of the posterior abdominal segments.

The male reproductive system lies dorsally and entirely within the abdomen(Fig. 1). No suspensory tissue was found except for tracheal (Trc ) branches.Newly developed females have the organs in a position similar to those of the malebut they extend slightly into the metathorax. A single suspensory ligament(SusLig) extends anteriorly from each ovary (0v) to the prephragma (Preph)of the metathorax (Reid 1958a; and Fig. 1). According to Reid the two sus-pensory ligaments unite at the prephragma. In the present study the exact attach-ment was variable, and in some specimens the two ligaments were fastened inde-pendently on each inside margin of the median notch of the prephragma.

As eggs develop the ovaries move towards the prephragma. Three pairs ofdorsal longitudinal flight muscles and the tergosternal flight muscles undergoautolysis at the time of early vitcllogenesis (Reid 1958a; Atkins and Farris 1962 ).

Volume 96 THE CANADIAN GNT011OLOGIST 479

This atrophy provides more room for the expanding ovaries and may contributenutritional material for growing oocytes (Ooc).

The posterior portion of the reproductive systems is supported by muscleand membranous tissues (Figs. 4, 19). These are attached to tergum VIII andsterna VII and VIII which form the posterior enclosure of the genital opening(GenOp) and anus (An) (Figs. 4, 18, 19).

In young females a tracheal network is more conspicuous over the posteriorhalf of the ovario'es than the a::tcrior half. During egg-laying this region expandsmost and the tracheal branches become more dispersed. Trachcation to the maleorgans was less noticeable. An important secondary role of the tracheae is tosupport the ovaries and testes (Tes) within the body cavity, especially during thecontractions of the muscular ducts.

Male Reproductive SystemThe major components of the male reproductive system are two testes (Tes),

each with a short vas deferens (Vd), three pairs of gland-like structures, two shortseminal ducts (Sm1D), a median ejaculatory duct (EjD) and a genital organ(Fig. 4).

Testis and vas deferens. The testes are dorso-ventrally flattened, bean-shaped,whitish structures measuring about 0.8 mm. at their maximum width. Eachtestis is divided into six equal follicles (Fol) (Fig. 8). At a median point on thetestis a vas deferens projects posteriorly as a broad tube which tapers to almostthe size cf the ejaculatory duct. Each vas deferens divides into two short vasaefferentia (Ve) within a testis and three testicular follicles appear to be continu-ous with each vas effcrens (Fig. 8).

An epithelial sheath (EpSh) covers the outer testis and vas deferens. It isgenerally thicker at the base of the vas deferens and is continuous with the septae(Sep) which separate one follicle from another (Fig. 8). The epithelial sheathresembles a loose reticulate membrane. It has many oval-shaped nuclei and restson a basement membrane.

The four zones of sex-cell development that are generally recognized for theinsect testis (Wigglesworth 1953) were not readily distinguishable but at leastthree of the more mature zones were seen (Fig. 14). The rate of development ofthe sex cells was similar in all follicles, with the earliest stage beginning at the outerextremity of each follicle and maturing toward the entrance of the vas efferentia.

During earl y sex-cell development membranous sheaths form around the sexcells and these later produce the sperm cysts (SpCsr) (Figs. 8, 14). The sperma-tozoa (Spz) develop within the cysts and at maturity the cyst membranes rup-ture near the entrance of the vasa efferentia. Dark irregularly shaped structuresbelieved to be remnants of ruptured cyst-cells were recognized near the base ofthe follicles (Fig. 8) but were not observed posterior to the vasa efferentia. Disinte-gration of the cyst-cells probably takes place after rupturing as reported elsewherefor insects generally (Imms 1957).

The vas deferens and vas effcrens are thick-walled tubes with an inner liningof large epithelial cells (Figs. 8, 17). No muscular tissue (Mel) was found on thewall of either of these tubes except near the posterior region of the vas deferens(Fig. 17). The anterior portion of the vas deferens becomes distended in allmature males and contains large masses of full y developed sperm (Fig. 17). Thistube and the vasa efferentia perform the function of sperm storage and thereforeconstitute the seminal vesicle (Smlv). Previous workers have referred to the mostposterior accessory gland (Figs. 2, 4, 15) in male beetles as the seminal vesicle(Hopkins 1915; Richmond 1935; Atkins and Chapman 1957; Ryan 1959), but

480 THE CANADIAN ENTOMOLOGIST March 1964

there was no evidence for this in I). monticolae. In tenerals the quantity of maturespermatozoa increased within the vasa deferentia and vasa efferentia for the firstfew days after emergence and after mating. Chapman (personal communication)separated sexuall y mature males of Try podendron lineatum (Olio.) from youngmales on the basis of sperm accumulation in the vasa deferentia and found nosperm \% ithin the "seminal resides". Francke-Grosmann (1950) reported thatthe vasa deferentia in D. n,itvus Kug. also perform the function of seminal vesicles("Sanlenhlase").

Tencral males are apparently sexuall y 'nature \\ hen they emerge from thehost tree since their testes always contain mature spermatozoa, but mating seldomoccurs before emergence (Reid I 958b). The time of sexual maturity in I).micans and in I). pseudotsngae Flopk. (Francke-Grosmann 1950; Vit6 and Rudin-sk y 1957) is similar to that in the mountain pine beetle.

LIST OF ABBREVIATIONS

Abd. abdomenAcGI, accessory glandAcGIA, accessory gland AAcG'AD, accessory gland A DuctAcGIAFI, accessory gland A fluidAcGIB, accessory gland BAcGIC1, accessory gland cellAn, anusAnch, anchorApod, apodemeArm, arm of anchorBcopx, bursa copulatrixBOr, basal orificeCho, chorionClt, corpus luteumClx, calyxCAlcl, circular muscleCmpAlcl, compressor muscleCon II Alm, connecting membraneCut, cuticleCyr. cytoplasm11D, ejaculatory ductEpPlg, epithelial pluglipSh, epithelial sheathFol, follicleFoIrpth, follicular epitheliumFun. funnelGen0p, genital openingGerm, germariumGpr, wonoporeIntSa, internal sac1111, 1.10.1%11 lobe of internal sacI aiMcl, longitudinal muscle1.0 y d, lateral oviductI.Pen, lateral lobe of penisI mu, lumen

- AL, muscles of male genitaliaAlcl, muscle\letath, metathorax

median lobe of internal sacAlOvd, median oviductMyct, mycetocyteNuc, nucleusNucl, nucleolus

Ooc, oocyteOst, ostitimOv, ovaryOvl, ovariolePcn, penisPrefolEpth, prefollicular epitheliumPreph, prephragmaRec, rectum

sternumScl, scleriteSensPen, sensilla of penisSep, septumSinn, seminal ductSmIrl, seminal fluidSmIRd, seminal rodStnl y , seminal vesicleSpcl, spiculeSpCst, sperm cystSpn, spineSpph. spermatophoreSpth, spermathecaSpthD, spermathecal ductSptliPm, spermathecal pumpSpthSa, spermathecal sacSpthVl, spermathecal valveSpz, spermatozoaSusLig, suspensory ligament

tcrgumTes. testisTgm, tegmen

1 -1Fil, terminal filament.Fnpr, tunica propriaTrc, tracheaTrct, trophocyteTrZn, transition zoneVag, vaginaVd, vas dcfcrensVe. vas efferensVit, vitellariumVitl, vitelline membraneX, possible gland structureXFI, fluid of X-structureV, possible sensory structureYlk, yolk

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TEE

T YEE

T

T Y

TIYAcGI

TesT ID

T II

TI

Figs. 1-4. I, Lateral view of male and female reproductive organs during copulation.2, Diagram of male accessory glands and ducts. 3, Transverse view of duct of accessory glandA, vas deferens and X-structure. 4, Ventral view of male reproductive system with genitalorgan in internal position.

482 TILE CANADIAN ENTOMOLOGIST March 1964

Mature spermatozoa are long and thread-like (a y. length 0.116 mm.) with in-conspicuous heads. They move through the vas deferens b y their own motilityand also by muscular contractions of the posterior vas deferens and ejaculatoryduct. The vas deferens leads directly to the funnel (Fun) mechanism (Fig. 2).

There is some variabilit y in the general morphology of the testes and vasaefferentia between Dendroctonus species as well as between individual mountainpine beetles. The vasa efferentia in D. valens Lee. are visible externally and eachtestis is subdivided into two equal lobes (Hopkins 1915). In D. mica-its the vasaefferentia are also visible external to the testes but each testis is a single unit(Francke-Grosmann 1950). The arrangement in D. psendotsugae (Ryan 1959)appears to be the same as that of the mountain pine beetle. Occasionall y 1).monticolete has each testis subdivided with short vasa efferentia visible external tothe testes. This variation was illustrated by Richmond (1935).

Male accessory glands. Three pairs of gland-like structures (AcGIA, AcGIB,X) were distinguished in male mountain pine beetles (Figs. 2, 15). Two of thesewere also located in six other Dendroctonus species and are similar in shape andposition on the seminal duct to those found in D. month- Ate. Two pairs of thestructures in the mountain pine beetle produced glandular secretions and aretherefore regarded as accessor y glands A and B, but the function of the thirdpaired structure (X) remains unknown (Figs. 2, 15). The more posterior of theseglands has been termed the seminal vesicle and the more anterior as a mucous oraccessory gland (I lopkins 1915; Richmond 1935; Ryan 1959).

Accessor y gland A. This is a conspicuous tubular structure about 0.13min. X 3.30 mm. (Fig. 4). Near the mid-length of this gland a short musculatedduct (AcGIAD) extends posteriorly to open into the funnel mechanism (Figs. 2,3, 4). The two end portions, usuall y partl y coiled, curve backward from theduct in the abdominal cavity. The tubular wall and the fluid (AcGIAFI) it con-tains appear uniform over the entire length. The outer wall has a thin membran-ous sheath of two layers that is underlain bs cuboid to columnar secretive cellswith large nuclei (Fig. 15).

The gland contents of most freshl y dissected mature males were milk y col-ored but in teneral males they were often semi-transparent. There was little dif-ference in the size of the glands between mature and teneral males. The glands ofmature males also became partl y transparent following mating and the transparentliquid turned milky upon contact with Ringer's solution. This fluid graduallyhardened to an elastic consistency. It was also heavier than water and slightlygranular and refractive. Stained secretion showed acidophilic characteristics.Similar properties have been recorded for the secretions of male accessory glandsof other beetles (Anderson 1950; Francke-Grosmann 1950).

When living beetles were dissected in Ringer's solution minute peristaltic-like movements were observed in the gland wall. This movement is probabl y afunction of the external sheath to eject the glandular fluid. During mating thisgland appears to contribute the largest component of the seminal fluid (SnilF1).

X-structure. This lies adjacent to the duct of accessor y gland A and is smalland bulbous. It enters the funnel mechanism via a short muscular duct in thesame manner as accessory gland A and the vas deferens (Figs. 2, 3, 15). Theanterior wall is thin, rigid, nucleated and yellow in fresh preparations. Anacidophilic substance (XFI) was usually present within the bulb portion. TheX-structure is unknown in other scolytids although three pairs of accessoryglands are not unc minion in the Polvphaga (limns 1957).

Accessory gland B. This is circular, flattened anteriorly and posteriorly,and has four to six well defined lobes (Figs. 2, 4). The lobes are protrusions of

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the outer wall which encloses a single cavity. The size of the glands varies de-pending upon the age and sexual activity of the insect; glands from newlydeveloped males or from those immediately after mating, tend to be smallest.Maximum widths in transverse section were 0.3 -0.7 mm.

Accessory gland B is semi-transparent and the fluid content is colorless andappeared to be miscible with water. The wall consists of thick epithelial cellsand often droplets of gland secretion arc visible as shown in Fig. 15. Otherinvestigators have suggested a glandular function for the corresponding structurein anicans and in T. lineatum, partl y on the basis of an absence of spermatozoawithin them (Francke-Grosmann 1950; Chapman personal communication).The term "middle gland" was suggested by Francke-Grossmann (1950) since thestructure lies intermediate between the external ejaculatory duct and the meso-dermal vas deferens. No spermatozoa were observed in this gland in the moun-tain pine beetle.

A second function of accessory gland B is to hold the posterior end of theducts from accessory gland A, the X-structure and the vas deferens in directalignment with the funnel of the seminal duct (Figs. 2, 15). The circular openingfrom accessory gland 11 is at the top of the funnel where it surrounds the region ofentr y of the three ducts (Fig. 2). During ejaculation it is probable that anintermixing of four materials takes place simultaneously.

Ejaculatory duct. The median ejaculatory duct (EjD) divides anteriorlyinto two short branches (Sm1D) and all portions appear to be identical in struc-ture and function. The two branches terminate at a median position on theposterior end of accessory gland B and are usually termed seminal ducts (Fig. 4).The ejaculatory duct is a thick-walled muscular tube which conducts the seminalfluid released from the testes and accessory glands (Fig. 10). Its wall consists ofseveral layers of circular muscles (CMcl) with an inner nucleated epithelium(Fig. 10B). No distinct intima was observed. The posterior end of the ejacu-latory duct is fixed to the genital organ.

Genital organ. The genital organ consists of four sclerotized structureswith associated muscle and membrane tissues (Figs. 4, 5), and conveys the seminalfluid to the female during coition. Its sclerotized parts include the penis (Pen),an accessory apparatus consisting of seminal rod (Sm1Rd) and anchor (Anch),the tegmen (Tgm) and the spicule (Spcl). The accessory apparatus lies withinthe penis and the tcgmen and spicule lie adjacent to the penis but are attached toit by muscle and membrane.

The penis is tubular with a basal orifice (BOO at the anterior rim and anostium (Ost) at the posterior end (Fig. 5). Two heavily sclerotized apodemes(Apod) extend anteriorly from the lateral walls of the main body of the penis.These serve as points of attachment for muscles connecting to all of the accessoryscleritcs associated with the penis except the spicule. Two prominent lobes(LPen) lie on the dorsal aspect of the penis and these were referred to as lateralfolds by Hopkins (1915). A median portion of the dorsum is also membranous(Fig. 11) and this may be homologous with the first connecting membrane(ConnMm), as it was termed by Metcalfe (1932). It is attached from the basalorifice rim to the posterior of the abdomen. A second membrane, or possibly acontinuation of the first, connects the penis to the tegmen. When the penis isinternal the first connecting membrane forms an outer sheath, but when forcedoutside the abdomen the anterior part of the penis slips through this membranepulling it inside out.

484 TILE CANADIAN ENTOMOLOGIST March 1964

The penis has three sensory areas (SensPen), one at the ventral posterior endand one on each of the dorsal lobes (Fig. 5). These areas have many short conicalsensilla (Fig. 7) which probably function as tactile receptors.

The internal accessory apparatus is fixed to the inner dorsal wall of the penisnear its posterior end and moves in a hinge-like manner. At this point the pos-terior margins of the anchor articulate with the terminal infolded portions of thepenis body — termed end plates by Hopkins (1915) and Francke-Grosmann(1948).

The internal accessory apparatus appears to serve three functions. It pro-vides posterior support for the ejaculatory duct, orientates the gonopore (Gpr)with the exterior of the penis and is a guide for the seminal fluid (SnilFI) duringcoition. Hopkins (1915) suggested a valvular function for the internal apparatusin D. valens but this was doubted b y Sharp and Muir (1912). No evidence wasfound to suggest a valvular function for either the seminal rod or the anchor inthe mountain pine beetle. The ejaculatory duct does not join the anterior endof the internal apparatus as suggested by Richmond (1935), but rather at a moremedian point on its dorsal side, and is attached to the anchor as well as to theseminal rod (Figs. 6, 13). This arrangement corresponds closely to the con-dition reported for D. micans (Francke-Grosmann 1948). The gonopore of theejaculatory duct lies between the arms of the anchor and the seminal rod(Fig. 6).

The internal sac (IntSa) is an important membranous component of thepenis. It connects to the arms of the anchor and encloses the internal accessoryapparatus. The ejaculatory duct is external to the sac except for the terminalend which is fixed to the accessory apparatus. The internal sac is also continuouswith the end of the penis (Figs. 11, 12). When fully everted for mating theinternal sac is seen as a thin, semi-transparent membrane with a large median lobe(MLb) that is partly bisected from the dorsal side and with two prominentlateral lobes (LLb). Two patterns of spin y sclerites are present on the outersurface of the lobes (Figs. 11, 12). The lateral lobes have an even distribution ofconical spines arranged individually and the median lobe has smaller spines inevenly spaced groups. The latter spines become smaller towards the posteriortip of the lobe and no sclerotizations were observed on its ventral side.

A small, circular, yellow structure (Y) lies at the posterior tip of the medianlobe and appears to serve a sensory function (Figs. 12, 16). The outer wall isfirm and may be partl y sclerotized. It is nucleated and cytoplasmic differentia-tion is suggested (Fig. 16). A similar structure was observed in D. micans byFrancke-Grosmann (1948) which she named the "epithelial body". She sug-gested that it serves a role in sensing and regulating blood pressure within theeverted sac.

The tegmen is a narrow, U-shaped sclerite located on the ventral side of thepenis with the ends curved dorsally. It is situated near the posterior end of theapodenmes (Figs. 4, 5, 9). Near its mid-length are two small anterior projec-tions. The tegmen provides muscle attachment and during copulation it ispulled to the posterior end of the abdomen.

The spicule is a prominent crescent-shaped, heavily sclerotized rod that iscircular in cross-section and has a central canal extending through most of itslength. It is slightl y enlarged at the anterior end where it rests in a median dorsalposition with the apodemes (Figs. 5, 9). From the anterior tip it curves laterallyand posteriorly and divides into two posterior prongs. The larger of these isbent transversel y near the posterior end of the penis on the ventral aspect, andthe smaller bends dorsally on the opposite side. The two prongs thus form a

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Lateral Ventral

9Figs. 5-9. 5, Lateral and ventral views of male genital organ in internal position. 6, Lat-

eral and ventral views of internal accessory structure of penis. 7, Typical sensillum of penis.8, Longitudinal section through a mature testis. 9, Dorsal and ventral views of male genitalorgan in internal position with musculature.

semi-loop around the penis. Muscles are attached to all three terminal points ofthe spicule as well as to the transverse portion of the larger prong. The spiculeprovides the major support for the genital organ (Figs. 4, 9, 10).

Musculature of the genital organ. Muscles M,, At and A1, arc paired and oneof each pair originates from near the tips of the two posterior spicule prongs(Figs. 9, 10). These hold the spicule relatively stationary. M, is attached to the

486 THE CANADIAN ENTOMOLOGIST March 1964

inside lateral margins of tergum M, connects to the inside lateral marginsof sternum VIII and M., extends ventrally and posteriorl y to sternum VIII.

A single muscle, M, is attached to both spicule prongs and completes a looparound the posterior end of the penis (Fig. 9). The connecting membrane passesbetween this loop and the penis. Relaxation and contraction of M, probablycontrols the rigidity of the genital organ while it is extended during matingactivit y . It also serves as a guide through which the penis can slide.

Muscles AL- and Ma also attach onto the spicule but oppose one another infunction. Ai., originates on the anterior end of the spicule and divides with onebranch passing around each side of the apodemes extending to the lateral arms ofthe tegmen (Figs. 9, 10). Muscle Me forms a single band extending from thetegmen to the transverse portion of the spicule. When the genital organ isinternal, Mo is relaxed while n is contracted (Fig. 9).

Muscle M, is paired, one muscle extending on the ventral side of the penisfrom each of the anterior apodeme tips to the anterior projections of the tegmen(Fig. 9). The ejaculatory duct passes between the two muscles to enter the penistube. Part of the function of these muscles is to retract the penis after copulation.They may also lessen lateral movement of the anterior end of the genital organduring copulation.

Muscles M. and M0 withdraw the internal sac after copulation. M. consistsof two large muscles that originate from the anterior tips of an apodeme (Fig. 9).They extend posteriorly within the penis tube where each divides into at leastthree branches. One branch from each muscle attaches to the anterior end ofthe internal accessory apparatus while the other two branches spread out over thelining of the internal sac (Figs. 11, 12). Muscle Mo is also paired and extendsfrom the inside lateral wall of the lateral lobes to the wall of the median lobe(Figs. 11, 12).

Eversion of the genital organ. Observations were made on the musculatureof the genital organ when fixed in the internal (Fig. 9) and everted (Figs. 10, I I,12) positions. Eversion begins with the contraction of Mo and At with a simul-taneous relaxation of M. Contraction of Mo probably causes a slight counterclockwise rotation of the penis to orientate the gonopore dorsally. The activitiesof these muscles project the penis posteriorly through the genital opening. Theanterior tips of the apodemes and the tegmen are pulled posteriorly to the trans-verse portion of the spicule (Fig. 10). A relaxation of M., and the lateral musclesof the eighth sternum probably facilitates the projection of the penis. .MusclesM,, M, and M., ma y also shift the spicule nearer to the posterior abdominal wall.At this stage the penis is at maximum extension for copulation (Figs. 10,

The internal sac is unfolded after the penis is extended. Eversion of the sacis probably caused by blood pressure with a simultaneous relaxation of musclesAl. and M. As the sac is forced backward the infolded posterior sclerotizationsof the penis fold out laterally, carrying the sac and the internal accessory appar-atus posteriorly . This movement swings the seminal rod and anchor backwardat a right angle to the penis. Francke-Grosmann (1948) suggested that thestiffening and pumping action of the muscular ejaculator y duct also helps to forcethe accessor y apparatus posteriorly. The internal sac finally unfolds in balloon-like fashion. bringing the gonoporc adjacent to a mid-dorsal point at the base ofthe median lobe (Fig. 1 ). The internal sac is completel y everted onl y when inthe vagina. Retraction of the male genital organ progresses in a reverse mannerto eversion,

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Figs. 10-13. 10A, Longitudinal ventral view of male genital organ in everted positionwith caudal abdominal segments. 10B, Transverse section of ejaculator y duct. 11, Dorsalview of male genital organ fu l ly everted. 12, Lateral view of male genital organ with Y-structure. 13, Transverse section through penis.

Female Reproductive SystemThe female reproductive system consists mainl y of two ovaries (0v), each

with a pair of ovarioles (0v1), a suspensory ligament (SusLig) for each ovary,two short lateral oviducts (LOvd), a median oviduct (MOvd), a bursa copulatrix(Bcopx), a spermatheca (Spth) and a pair of accessory glands (AcGI) (Figs.18, 22).

488 I I IE CANADIAN ENTOMOLOGIST March 1964

Oviducts. The median oviduct extends from the posterior genital opening(GenOp) to the base of the ovaries where it divides into two lateral ducts (Figs.18, 22). They consist of an inner layer of longitudinal muscle fibers (LnMcl)surrounded by several layers of circular muscles (CMcl) (Fig. 25). The innerwall is convoluted when relaxed and is lined with a heavily nucleated epithelium..Minute spines line the epithelium with a posterior orientation and are mostnumerous near the caudal end of the median oviduct. The musculature sur-rounding the posterior opening of the oviduct is greatly thickened (Fig. 19)forming a sphincter t ype of mechanism which closes the oviduct off from thegenital opening and from the vagina.

Copulatory pouch. This is dorsal to the posterior end of the median oviductand includes the vagina (Vag) and bursa copulatrix (Bcopx) (Fig. 19). Thereis a single external opening common to both the vagina and the median oviductand a portion of the walls of these two tubes is united with muscle tissue (Fig.19). The muscular wall of the vaginal region is thinner than the wall of theoviduct and may consist onl y of circular muscles on its dorsal side. Thickenedmusculature surrounds the posterior end of the vaginal tube (Fig. 19).

The bursa copulatrix forms a dorsal diverticulum that is continuous with thevagina. It is blind at the anterior end, slightl y longer than one millimeter and indorsal view curves to the left (Figs. 18, 22). It resembles the oviduct in cross-section but onl y one layer of outer circular muscles could be found (Fig. 26).The inner convolutions appear to consist mostl y of thick membranous tissue withlarge nuclei. Some longitudinal muscle fibers are also likely to be present. Themembrane surrounds the inner wall of the vagina as well as the bursa copulatrixand carries numerous spines that are larger than those of the median oviduct.These spines occur only on the dorsal wall of the vagina and the y project an-teriorly. The muscular wall is slightly constricted near the basal end of thebursa copulatrix and immediately posterior to this are two spiny sclerites (Sd)attached to the inner wall (Figs. 22, 27). When the bursa copulatrix is emptythe sclerites occup y a lateral position (Fig. 27) with their spines almost touching.When it is filled they may move to a dorsal position (Fig. 22). The scleritesare convex and carry about ten well defined spines on the outer curvature (Fig.21). These curve posteriorly within the lumen of the bursa copulatrix.

Examination of five other North American species, including D. brevicomisLee., I). pseudotsugae Hopk., D. simplex Lee., D. engeinzanni Hopk. and D. mur-rayanac Hopk., showed that only the first three possessed sclerites in the bursacopulatrix. Hopkins (1915) had earlier found them in D. valens. Sclerites ofthe bursa copulatrix are also 'widel y known throughout the Elateridae (Stein1 847 ; Williams 1945; Becker 1956; Karg 1962).

Accessory Glands. Only one pair of accessory glands (AcGl) was foundin the female. These are located near the posterior end of the reproductivesystem and open laterall y from the lower region of the vagina (Fig. 24A). Whenempty they are small and wrinkled (Fig. 18) and when filled they are greatlydistended and elongated on the antero-ventral side (Fig. 22). The glands ofteneral females are empty, but glands during and after egg-la y ing and in over-x% interim); females are at least partly filled. There is no distinct duct connectionbetween the glands and the vagina, rather the gland openings are loose and theirperipheral wa lls are lined with long spines (Spn) that project toward the glandinterior (Fig. 24A).

The accessory glands are lined with densel y packed, dome-shaped cells(AcGICI), each with a short spine at the tip (Figs. 24B, 24C). 1 1 Iw cells adjacentto the gland opening become smaller and their spines correspondingl y larger.

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pf,

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Figs. 14-17. 14, Section through a mature H, \ Ieihm longitudinalsection of male accessory glands; X120. 16, Section through V-structure of internal sac;X440. 17, Longitudinal section of vas deferens (seminal vesicle) from a mature male; X120.

I.arge nuclei were evident at the base of the cells and a cytoplasmic substance waspresent in the dome portion. Surrounding the outer gland ^vall is a basementmembrane which imparts a smooth appearance.

It was not determined whether there was any secretion from the gland cells,but substances including chorion membranes (Cho), yolk-like material 1 Ylk),remnants oF spermatophores (Spph) and spermatozoa (Spz) were recognizedwithin the glands. These materials accounted for much of the increased volume(Fig. 29). As many as seven chorion membranes were found in the glands. Inanother instance six spermatophores were found in a female, one in the vagina,four in one accessory gland and one in the other. This occurred when femaleswere stored with a larger proportion of males. The elongated spines surroundingthe accessory gland opening probabl y prevent outward movement of the contentsand may help in its maceration.

When egg production was halted in females by rapidly dr ying the barktissue the accessory glands invariably contained chorion membranes and y olk-like material. These materials accumulated at variable rates and were often in onegland more than in the other. If the females were left for several da ys much ofthe accessory-gland content consisted of a yellow oil yliquid which usuallyseparated from the rest of the gland content. This condition often appeared inegg-laying females collected from infested logs during the summer as well as in

499 I I I I . , CANADIAN ENTOMOLOGIST A I areh 1964

females in the over \\ intering period. Nine females collected in November 1960all showed either partl y or full y expanded glands (Fig. 22) with yellow content,.This fluid was immiscible and floated in Ringer's solution and had characteristicsFimilar to the corpus luteum. The presence of the yellow fluid may suggest thatautolysis had taken place. The foregoing evidence suggests that the function ofthese glands is to Cl/MCI-VC nutrient material by operating in a digestive and re-absorbing capacity.

Previous workers termed the female accessory gland in the mountain pinebeet'e "colleterial" (Richmond 1935; Reid 1958a) but such terminolog y was notsupported by the present study. There was no adhesive substance found on thesurface of eggs. No reports of a nutrient conserving function for the femaleaccessory glands of other bark beetles could be found in the literature. Chap-man (personal communication) observed spermatozoa in the "colleterial" glandsof T. lineatum and Francke-Grosmann (1950) reported that a yellowish fattysubstance occurred in the colleterial glands of D. micans. She suggested that thesubstance acted as a lubricant during oviposition and copulation.

Sy mbiotic organisms occur in association with the reproductive organs ofman y insects (Buchner 1953; Schlottman and Bonhag 1956; Richards and Brooks1958; Bonhag 1959; Aslam 1961) and according to Aslam symbiont-containingstructures arc present adjacent to the vagina in two scolytid subfamilies. Noprotozoan-like structures were observed in the female accessory glands of themountain pine beetle, but a structure resembling a mycetocyte (Myer) isillustrated in Fig. 37. This structure lies between the follicular epithelium(FolEpth) and the ovariole sheath (EpSh) in a mature adult and is similar to themycetocy tes illustrated in the cockroach ovary (Bonhag 1959).

Spermatheca. The spermatheca is usually seen curved to the right of themedian oviduct when viewed dorsally (Figs. 18, 22). It consists of a pump organ(SpthPm) with compressor muscles (CmpNicl) and a sac (SpthSa) (Fig. 20).The spermatheca stores sperm and releases it for fertilization. The pump organis a U-shaped, sclerotized capsule with a small projection at its distal end and aduct (SptliD) extending from its proximal end (Fig. 20). The compressormuscle extends from the sclerotizcd projection to the basal portion of the cap-sule. On the inner surface of the posterior half of the capsule, scierotization isirregularly thick (Fig. 20), a condition which appears necessary to ensure bend-ing in the proper plane during pumping action. The pump organ is containedin a thin nucleated epithelial sheath ( EpSh) (Fig. 20). The spermathecal sacextends from the outer curvature of the pump organ where it surrounds a smallvalve-like opening (SpthVl) (Fig. 20). It is thick-walled, nucleated and vacuo-lated (Fig. 20), which suggests a glandular function. Hopkins (1915) termedthe pump organ in D. ,z'alcus the "spermatheca" and the sac portion the "sper-mathecal gland". Richmond (1935) showed that the structure of the sper-matheca of D. wonticolae was identical with that of D ..T. ,alens, but referred to thepump organ as the "spermathecal sac". In the present study the pump organand the sac were designated as the spermatheca proper on the grounds that livingspermatozoa are stored in both structures simultaneously (Fig. 20). The sacmay provide nutritive material for sustaining the spermatozoa while the pumporgan appears to perform the function of sperm ejection. Franckc-Grosmann(1950) suggested that the sclerotized pump in I). micans ma y act both ways, i.e.the spermatheca is tilled and emptied by pumping.

The spermathecal duct passes posteriorl y from the pump organ and mediallybetween the vaginal chamber and the median oviduct. It opens into the medianoviduct below the posterior end of the vagina (Fig. 19). The duct is cylindrical

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0.02 mm.

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EpSh

SpthD

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Figs. 18-22. 18, Ventral view of reproductive system oflongitudinal view of median oviduct and copulatory chamberview of muscles and sclerites superimposed. 20, Longitudinal21, Lateral view of a spiny sclerite of bursa copulatrix. 22,system from a fully develoned female during early winter.

a teneral female. 19, Medianwith a longitudinal tangentialsection through spermat . eca.Dorsal view of reproductive