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Mem. Qd Mus. 21(2): 361-85. [1984]

AN INTERPRETATION OF THE STRUCTURE AND FUNCTION OF THE

ANTENNAL SENSE ORGANS OF MELITTOBIA AUSTRALICA (HYMENOPTERA:

EULOPHIDAE) WITH THE DISCOVERY OF A LARGE DERMAL GLAND IN THEMALE SCAPE.

EDWARD C. DAHMSQueensland Museum

ABSTRACT

The importance of the antennae during courtship behaviour of Melittobia species promptedan investigation into the histology of the enlarged male scape using the single Australianspecies Melittobia australica. The application of the male scape during courtship suggests apossible chemical communication between the antennae of the two sexes. Histological andSEM work reveal the presence of a large dermal gland in the male scape. SEM work andchemical applications reveal the presence of long thin unfluted setae, tapering fluted setae,multiporous plate sensilla and short basiconic capitate pegs on the antennae of both sexes (theshort basiconic capitate pegs are absent in most males). Together with behaviouralobservations these are used to suggest the possible structure and function of the antennal senseorgans and the most likely receptor for the male scape pheromone.

MALE SCAPEAmongst the parasitic Hymenoptera, male

antennation is a common component ofprecopulatory behaviour and it reaches a highexpression in Melittobia (Gordh and DeBach(1978)). The enlargement of the male scape and itsapplication discussed by Dahms (1983b) suggestthat it has a function in stimulating the female'santennae. In males of all species cleared in 10 07oNaOH the scapes show a clear delimited zone (Pl.la, M. australica). In M. australica the surfaceappears to have a cellular pattern at highermagnifications. Since all internal tissue isremoved in this process, the clear delimited zonesmust be cuticular which suggests mechanicalstimulation of the female's flagellum. However,freshly killed M. australica males used for AgNO,staining to test for touch chemoreceptors whenexamined after 30 minutes in Toluene were foundto be not completely cleared. In the scapes ofthese males could be seen a cellular-like zoneoccupying the same area as the clear delimitedzone in NaOH cleared specimens. (Pl. la) is alateral view of the side opposite pedicelattachment and (Pl. lb) is an end view of the sameside. This cellular-like zone was absent inspecimens fully cleared in Toluene indicating thatit was internal tissue. Serial sectioning of male M.australica scapes clearly shows large dermal

glands which follow the clear delimited zone inNaOH cleared specimens (Pl. 3b, c; 4a). Thesections also show that the inner cuticular liningon the scape groove is much thinner than theouter cuticle and that there are cuticularinfoldings along the length of the gland. Thesecuticular infoldings form the limits of the clearzone in NaOH cleared specimens.

To prepare them for SEM examination, maleswere treated with 10 07o NaOH until cleared toremove any glandular secretions which mightobscure the cuticular surface of the gland. Theywere then dehydrated in alcohol and finallytreated with Toluene to remove any wax whichmight obscure cuticular pores. Males were airdried and mounted upside down on stubs inpreparation for gold coating. It was noticed thatafter removal from Toluene and air drying theflexible intersegmental cuticular areas becamewhite while the thicker cuticular scleritesremained yellow-brown. The lining of the scapegroove became white indicating that it wasflexible thin cuticle, which would explain thecuticular infoldings around the gland for support.SEM photomicrographs (Pl. 2b, c; 3a) show thecuticular surface over the gland to be welldifferentiated and perforated by numerous pores.At higher magnifications the cuticular surfaceover the gland shows a somewhat reticulate

362^ MEMOIRS OF THE QUEENSLAND MUSEUM

appearance. Noirot and Queenedey (1974)mention cuticular specialisations in Heteroptera,Blattodea and butterflies associated with dermalglands and that these serve as evaporative areasensuring rapid evaporation of secretions. Thecuticular area over the scape gland in M.australica fits this pattern.

The shape, size and position of the scape glandvaries with species and provides a very usefultaxonomic tool. I refer the reader to mytaxonomic revision of the genus (Dahms 1983a)for a fuller discussion together with figures and adiscussion of species groups.

Van den Assem et alia (1982: 458) raise a ratherinteresting point. They found that males withtheir antennae removed do court females andinduce receptivity. From this they concluded thatstimuli which might arise from them are by nomeans necessary. The data they present are frommutilation experiments with M. acasta (Walker)and it is not clear from their account if theycarried out similar trials with all species at theirdisposal. If we look at the male scape gland in M.acasta it is not as extensive as in the hawaiiensisand assemi groups. The cuticle over the scapegland in M. acasta as shown by Van den Assem etalia (1982, Pl. 1) does not appear to have anevaporative function as it does in M. australica(Pl. 2c, 3a). Perhaps the scape gland does nothave the importance in the acasta group that ithas in the hawaiiensis and assemi groups. It isinteresting to note also that antennal contact ispermanent throughout courtship in thehawaiiensis and assemi groups but only throughpart of the cycle in M. acasta and M. evansiDahms (1983a) but not in M. digitata Dahms(1983a). There may be some variation in theimportance of permanent antennal contact insome members of the acasta group (not studied byVan den Assem et alia (1982)) which seem to haverelatively expanded scape glands eg. M. femorataDahms (1983a) and M. chabylii Ashmead. In thelatter the scape gland in genicualte as in thehawaiiensis and assemi groups although that ofM. chabylii is not as extensive.

Goodpasture (1975) observed pores in themodified scapes of the torymid chalcidoid waspsMonodontomerus montivagus Ashmead and M.clementi Grissell which were applied to the tip ofthe female flagellum during the climax phase ofcourtship. He concluded that the male scapesmight be the source of chemical communicationas a behavioural cue and further suggested thatthe pores indicated either a chemical sensoryfunction or pheromone elaboration sites. From

my studies on M. australica I suggest that they areprobably the latter. Antennation during courtshipis a common phenomenon in Chalcidoidea and isoften accompanied by antennal modifications.Pheromone glands in male antennae may also bea common occurrence. Houston (1975) has foundantennal modifications containing dermal glandsin several Australian species of the bee genusHylaeus. Antennal modifications containingglands may be more widespread in theHymenoptera than current knowledge indicates.

ANTENNAL SENSE ORGANSDuring the course of a biological study on M.

australica Dahms (1983b) it was decided toinvestigate the sense organs on the antennae sincethe latter play an important part in precopulatorybehaviour. The following discussion is based onSEM work, behavioural observations and a fewchemical applications. It does not have the benefitof histological or electro-physiological data,therefore the structures and functions of the senseorgans are suggested rather than conclusivelyproven.

Males of all species of Melittobia have theircompound eyes reduced to a single ocellus-likespot. Picard (1922) examined M. acasta maleshistologically and found that the reduced eyeslacked the normal structural elements of even anocellus. The optic ganglia were also reducedrelative to the female. He related this reduction,together with shortened wings and relativelyreduced pigmentation, to the male's restriction tothe host cell or puparium in which they emerge.This reduction in functional elements in the eyesof males is no doubt general in the genus.

The sole function of the male is related toreproduction. Van den Assem and Putters (1980)found that sound production is not involved inthe courtship of Melittobia. Presumably malesrely on chemical and tactile stimuli for locatingfemales and for precopulatory behaviour.Chemical information appears to play animportant role in the behaviour of both sexes.The size of the complex gland in the male scapeand the role of this segment during precopulatorybehaviour suggests that the female receives aconsiderable chemical input during antennation.Behavioural observations (mentioned under'Long thin unfluted setae' below) indicate that thesexes are chemically different and there are easilydiscernible behaviour patterns depending on thesex encountered by individuals of both sexes.Females have additional occasions in whicholfactory reception could be important e.g. host

DAHMS: ANTENNAL SENSE ORGANS OF MELITTOBIA^ 363

location and feeding. The antennae of both sexeshave setae whose structure suggests tactilereceptivity.

SEM examination of the antennae of males andfemales of M. australica revealed the presence ofthe following sensory structures:-

1) long thin unfluted setae2) tapering fluted setae3) multiporous plate sensilla4) short basiconic capitate pegs

1) Long thin unfluted setae (Pl. 5b,)These are readily distinguished by the absence

of both a basal socket and fluting. They are onlypresent on the club of both sexes especially at thetip of the terminal segment.

Lack of a socketed base suggests they are nottactile in function. A possible contactchemoreceptive function is suggested by theirconcentration at the tips of the antennae,particularly noticeable in males, and bybehavioural observations.

A male can instantly distinguish between thesexes by tapping another individual with the tipsof his antennae. His behaviour variesdramatically according to the sex encountered;another male induces aggression, a female ismounted.

Females can also distinguish between the sexes.Virgin female M. australica when confinedwithout males stand around with their mandiblesopen. When provided with a dead male pupa theyimmediately become active and begin searchingbehaviour. When another female is encounteredthey stop, palpate the encountered female withthe tips of the antennae then resume searchingbehaviour. When the dead male pupa wasencountered and palpated, searching behaviourceased. The females stood around the pupacontinually palpating it with the tips of theirantennae. Some of the females opened theirmandibles. In cultures, similar reactions occurredand it was not uncommon to see groups offemales standing around a male engaged incourtship, palpating him with the tips of theirantennae. Mandibular opening was also observedin these groups of virgin females and it suggeststhat mandibular glands could be the source of afemale odour. Gordh and DeBach (1978)mentioned that mandibular involvement incourtship appears to be an adaptation in someChalcidoidea; also studies showed that olfactioncould be used for mate attraction. They suggestedthat the gland-like ducts in the mandibles ofchalcidoids may indicate exocrine glands. Themandibles of both sexes in Melittobia have two

such gland-like ducts. During courtship in M.australica, mandibular opening by females occurstowards the end of the sequence which bringsthem into close proximity with the flagellum ofthe male.

Female behaviour on a host also suggests acontact chemoreceptive function for thse sensilla.A fertilised female uses her ovipositor to puncturethe host then feeds on the droplet of host bodyfluid that wells forth. After withdrawal of theovipositor the female moves backwards palpatingthe surface of the host with the tips of herantennae until the droplet is encountered. At thispoint feeding begins. Female M. australica revisitold puncture sites to feed upon congealed hostbody fluids which they relocate by palpation withthe tips of their antennae.

SEM examination of the tip of these setae doesnot reveal the typical pores of contactchemoreceptor sensillae. Following theprocedures of Slifer, Prestage and Beams (1957)very good results were obtained using AgNo,.After 60 minutes, the AgNo, had penetrated thetips of these setae (Pl. 5a). The penetration wasmore rapid in males than in females which isprobably related to the setae being of largerdiameter in the males. These tests, behaviouralobservations and location of these setae suggesttherefore that they are touch chemoreceptors.

In the female, touch chemoreceptors on theterminal antennal segments would also be of usein host identification. Female M. australica walkover a host nest palpating it with their antennae.Once it has been identified and entered thesesensillae may be of use in detecting the presenceof enveloping membranes, e.g. cocoons. Theymay also help differentiate hosts e.g. ovipositionbehaviour differs between hymenopteran andsome dipteran hosts. Should a Melittobia femaleenter a host cell when the host is immature thesesensillae would allow her to distinguish betweenthe host and its provisioned food. The relativeamount of food provision and its state ofpreservation may be of use in distinguishing if thehost had failed or its stage of development. Onthe other hand these sensillae may be used directlyto ascertain the age of the host. No information isavailable on whether there are chemicaldifferences between the different stages of a host,but since the hymenopteran hosts I have observedaccumulate waste internally and pass it out justbefore pupation as meconium, the relativeamount of internally accumulated waste or thepresence of meconium may be an importantsensory signal for oviposition in Melittobia.


Finally these sensilla may be useful in detectingthe suitability of a host i.e. whether the host isdiseased.

2) Tapering fluted setae (Pl. 5b, ii)These arise from a socketed base and show a

slightly whorled fluting on the surface (Pl. 6d).They do not take up AgNO, stain. The flutingprovides rigidity allowing the setae to resistbending thus transferring maximum movement tothe socketed bases. In the male they are presenton all antennal segments with markeddifferentiation. On the proximal segments of theflagellum they are long and numerous, but arereduced in length and number towards theterminal club segment (Pl. 6a). On the othersegments of the antenna they are also relativelyshorter and are fairly evenly distributed except fortheir absence on the lining of the scape grooveand for a relatively denser arrangement ofshortish setae on the upper surface of the lateralexpansion of the pedicel. In the female they arepresent on all segments of the antenna and have afairly even distribution (slightly fewer on the club)without any size differentiation. In general, theyare shorter and finer than in the male and they areshorter and finer than the long thick non-flutedsetae on the clubs of both sexes.

Because of the fluting and socketed base Iassume they are touch receptors. Their generaluniformity in size and shape in the femaleindicates they have no specific function, justproviding generalised tactile information, e.g.they would be of assistance in estimating the sizeof the hole the female excavates in the host cell. Inthis way the female would be able to estimate ifthe excavation is wide enough and whenpenetration has been effected. Female M.australica when excavating in a Sceliphronform osum nest were noted to insert theirantennae periodically and touch the walls of theexcavation with the sides of the flagellum.Differentiation of these sensilla on the maleflagellum suggests a specific function. When amale encounters a female he mounts her first thensearches for her head with his antennae. When hemounts a female he orientates longitudinally onher and taps his flagella either side of the female'sextremity like a pair of cupped hands thusengaging the long setae on the proximal flagellarsegments. When the female's posterior metasomais touched the male turns 180 0 and repeats theprocedure at the head then scoops her antennaeinto his scape groove. Where the female's head istouched no turning occurs. This may not be the

only sensory input e.g. if the female produces afemale scent from mandibular glands thenorientation on the female could also involveolfactory information via his multiporous platesensilla.

Before passing on to the other sensilla, mentionshould be made of two clusters of differentiated,socketed, fluted setae occuring on leg segments inthe male. In M. austratica and M. hawaiiensismales the ventral surfaces of the fore-trochantersbear a dense tuft of thick, short, socketed setaewith whorled fluting (Pl. 4b). In males of all otherknown species except M. chalybii where they arenot as well developed the fore-trochanters have afew fine, undifferentiated, scattered setaeventrally. During courtship of M. australica andM. hawaiiensis these setae press firmly down onthe pronotum of the female. In all other speciesfor which courtship is known, the position of themale is such that the fore trochanters are not incontact with the female. It is difficult to suggestthe use that these serve, but since modifications inmale Melittobia morphology are closely linked tosome aspect of courtship there must be someimportant sensory input via these setae. Perhapsthey are useful in positioning the male forcourtship.

Another group of differentiated, fluted setaewith socketed bases occur on the posterior ventralsurfaces of the mid femora of males of all speciesand ventrally on the mid trochanters of all speciesexcept M. australica and M. hawaiiensis. Thoseof M. australica are definitely socketed withshallow, unwhorled fluting (Pl. 4c). These setae inall species are much longer than the general bodysetation and there is some differentiation amongstthem. The mid legs are used by the males of allspecies during courtship and in M. australicathese setae were noted to brush the 'shoulder'junction of the pro- and mesonotum of thefemale. The pattern of distribution and the degreeof differentiation amongst these setae varies withthe species Dahms (1983a). It would be interestingto see if these variations are related to specificdifferences in male mid leg movements and/or theparts of the females brushed. Their function inthe male may be to signal contact with that part ofthe female to be stroked and their input to thefemale would most likely be tactile also via herundifferentiated general body setation. Femalesdo show differentiated long setae on the posteriorpronotum, the mid-lobe of the mesoscutum andthe scutellum, but these are not in a position to bestimulated by the differentiated mid leg setae ofthe male.


3) Multiporous plate sensilla (plate organs) (Pl.5b, iii).

These are raised sensilla which appear as paleareas on dry and slide-mounted antennae of mostHymenoptera. In Melittobia they are elongate(0.009 x 0.003 mm) on female club segments ofM. australica) and are present on all flagellarsegments in both sexes except for males of the M.hawaiiensis and M. assemi groups where they arerestricted to the club segments only. On thefunicle segments they tend to be orientatedtransversely and in general they are fewer innumber than on the middle club segment. On theclub segments they tend to be longitudinal inarrangement and the transverse arrangement onthe funicle segments may be related to the smallernumber per segment. Distribution on eachsegment is uniform, i.e. there is no accumulationon any one side. The pattern of distribution alongthe antenna seems to vary with species and there isa small amount of intraspecific variation.

Multiporous plate sensillae have been assignedvarious functions, e.g. mechanoreceptors (Merlin1941), auditory receptors (Ruland, 1888), airpressure receptors (McIndoo 1914, 1922),photoreceptors (Booth, 1963) and so on. Morerecent work indicates an olfactory function. Thereaction of M. australica multiporous platesensilla to ethyl acetate (discussed later) certainlyindicates a reaction to chemicals.

Studies by Slifer, Prestage and Beams (1959)showed that some of the peg sensilla on theflagellum of grasshoppers had numerous finepores in their cuticular walls and these could bedemonstrated by soaking the antenna in 0.5%methylene blue. Sections revealed fine nervefibres running to each pore. Further work hasshown these to be olfactory receptors. Electro-physiological work by Lacher and Schneider(1963) and Lacher (1964) has shown that themultiporous plate sensilla on honey bee (Apismellifera) antennae are olfactory. Slifer andSekhon (1961) demonstrated fine pores in thecuticle of these, but not the fine fibrils. Slifer(1969) felt that further examination will probablyreveal fine fibrils passing to these pores.Multiporous plate sensilla in aphids examined bySlifer, Sekhon and Lees (1964) differ in structurefrom those of the honey bee partly in thepossession of an inner and outer cuticular layer.Dedrites pass singly or in groups through pores inthe inner cuticular layer and enter a fluid filledchamber between the two cuticular layers inwhich they branch repeatedly. The fluid filledchamber has some importance in interpretingresults obtained when I treated M. australica

females with ethyl acetate (discussed later). Theouter cuticular layer of aphid multiporous platesensilla are penetrated by numerous fine poreseach supplied with fine fibrils. It could not bedetermined if these fine fibrils were connected tothe dendrites, but Slifer, Sekhon and Lees (1964)felt this was probably the case. Freshly moultedspecimens admitted crystal violet dye throughthese pores. The presence of fine filamentsterminating in the pores plus the staining via thesepores were taken to indicate an olfactory functionfor aphid multiporous plate sensilla.

Slifer (1969) examined the sense organs on theantennae of the pteromalid wasp Nasoniavitripennis (Walker). When treated with 0.5%crystal violet dye the stain rapidly entered themultiporous plate sensillum and examinationshowed the presence of numerous fine pores inthe surface. In cross section these multiporousplate sensilla were seen to have an innermembrane similar to the multiporous platesensilla of aphids. The inner cuticle lies just abovetwo shelf-like invaginations of the cuticle. Shenoticed a large group of dendrites just below theproximal end of the inner membrane andpresumed that these passed through the innermembrane, as in the aphid, and sent filamentsinto the pores in the outer surface.

The multiporous plate sensilla of M. austraticaresemble those of Nasonia vitripennis in overallshape and appearance. In cleared specimens, twolongitudinal cuticular invaginations can be seenon either side of the multiporous plate sensilla asin N. vitripennis. I have not carried outhistological investigation of the M. australicamultiporous plate sensilla to confirm the presenceof an inner membrane but am fairly certain thereis one. Attempts to demonstrate pores in the outerwall using 0.5% crystal violet solution as used bySlifer (1960, 1969) were not successful even infreshly moulted specimens and SEMinvestigations did not reveal pores either. Slifer,Sekhon and Lees (1964) found that the plateorgans of aphids showed crystal violetpenetration when fixed four hours after the finalmoult but no penetration at 24 hours and 48hours after final moult. They suggested that theminute pores in the older specimens might berimmed with a waxy or hydrophobic materialwhich prevents entry of the dye. Locke (1964)when discussing the formation of the insectcuticle states that the secretion of the endocuticleand the secretion of wax can occur concurrentlyand extend through the intermoult period.Therefore, it is possible that wax secretionsconstrict the pores after moulting. Pl. 8a-c show


the thin walled basiconic pegs of the grasshoppersAtractomorpha similis (Bolivar) freshly moultedand Valanga irregularis (Walker) several hoursafter moulting. The difference between the two isthought to be a result of wax encroachment. Goldcoating would further fill the fine pores andobscure them in older specimens.

The normal method used for preparing M.australica for SEM examination involved killingby immersion in 75% ethyl alcohol before goldcoating. When freshly moulted specimens werekilled using ethyl acetate vapour before goldcoating the result showed multiporous platesensilla with a crumb-like surface which at highermagnifications look like exudations from pores inthe surface (Pl. 6b-d). It can be seen that thesurface of the antenna lacks the usual crazedappearance of older antennae and this is thoughtto be because the wax layer was absent or verythin. Older specimens when killed with ethylacetate showed multiporous plate sensilla with ablistered appearance and distribution of theblisters matched distribution of the exudations infreshly moulted specimens (PI. 6d). It is thoughtthat the exudations arise from the fluid filledspace between the outer and inner membranes ofthe multiporous plate sensilla and that this is inresponse to fairly high ethyl acetate concentrationbeing an attempt to protect the sensitive nerveending from a pungent vapour. The analogy is tothe mammalian nasal mucosa which producescopious mucus in response to pungent vapours.

Barlin and Vinson (1981) investigated themultiporous plate sensilla on the antennae ofseveral species of Chalcidoidea. In some casesthey also found that the presence of pores in theouter plate was shown by exudations. Theirinvestigations revealed two types of multiporousplate sensilla; Type 1 - present in both sexes andpossessing a thin outer cuticle with numerouspores; Type 2 - present in females only andpossessing a thick outer cuticle with fewer pores.Both types were found in all species studiedexcept three i.e. not all species were found to haveType 2 multiporous plate sensilla. In M.australica, the females appear to have only Type1. However, my work on M. australica antennalsense organs was carried out some time before theappearance of the paper by Barlin and Vinsonand time does not permit a more thoroughinvestigation of this aspect. I have notinvestigated the multiporous plate sensilla on themale antennae.

The similarity of the multiporous plate sensillaeof M. australica to those of Nasonia vitripennis,the presence of pores on the outer surface in

conjunction with the results of Slifer et alia onother receptors having porous surfaces and theresults of Barlin and Vinson with variouschalcidoids suggest strongly that the multiporousplate sensilla of M. australica are olfactory infunction. From their reaction to ethyl acetate theyare probably very sensitive.

Before discussing their function we should lookat the short basiconic capitate pegs as theseappear also to be olfactory in function.4) Short basiconic capitate pegs (Pl. 5b, iv).

These organs are absent from the antennae ofmales of most species but are present on thefunicle and club of females where theypredominate on the dorsal or outer surface. Theyarise from a circular, shallow, relatively broaddepression in the cuticle. Thereafter the pegtapers into stalk which terminates in a sphericalknob, the whole resembling a champagne cork.They occur sub-marginally on the distal portionsof the segments and are directed towards thedistal tip of the antenna.

These were not recorded on the antennae ofNasonia vitripennis by Slifer (1969) but werefound subsequently in this species and anotherpteromalid wasp Peridesmia discus (Walker) byMiller (1972). Weseloh (1972) found them on theantennae of the encyrtid wasp Cheiloneurusnoxius Compere. Neither gave any details of theirultrastructure but Miller (1972) assumed theywere not touch receptors because of theirsheltered location. Slifer, Prestage and Beams(1957,1959) suggest that basiconic capitate pegsmay function in olfaction if they are thin walledor in the perception of irritant substances if theyare thick walled.

When females of M. australica were killed byimmersion in 75% ethyl alcohol, SEMexamination showed no details other than acrazed surface thought to be wax (Pl. 7a). Freshlymoulted females killed with ethyl acetate vapoursshowed weeping from slits or rows of poresarranged along the longitudinal axis of its capitatetip or caput. In Pl. 7b-d these slits or rows ofpores can be seen quite clearly. The distal tip ofthe caput was devoid of exudations and resembleda tonsure. Around the base of the peg wereexudations resembling those of the multiporousplate sensilla.

If one is to accept the reasoning put forwardearlier to explain the exudations frommultiporous plate sensillae then the internalstructure and the function of the short basiconiccapitate pegs may be the same as the multiporousplate sensilla. They are undoubtedly olfactory infunction. Therefore there are two


morphologically different olfactory sensilla onthe antennae of all females and some males.

Schneider and Steinbrecht (1968) whendiscussing insect olfactory sensilla indicated thereare two physiological types of olfactory cells —odour specialists and odour generalists. Theformer respond to biologically important odours,e.g. sex attractants, warning or specific foododours. Both types may be found in the onesensillum and this has been demonstrated in themultiporous sensilla of the honey bee Apismellifera.

In Melittobia, evidence suggests specific andsexually different chemical signals. The sourcesare the male scape gland and circumstantialevidence indicates mandibular glands in bothsexes. These would suggest the presence of odourspecialist, olfactory cells. Electro-physiologicalwork would be required to identify the presenceand location of these cells but some speculation ispossible.

In the males of most species the antennae lackshort basiconic capitate pegs. In females these arelocated mostly on the upper surface of theantennae which is the surface applied to the innerlining of the male scape groove or cup containingthe dermal gland. The short basiconic capitatepegs therefore might contain odour specialistolfactory cells for perception of a malepheromone. Females are able to detect malesfrom a distance, e.g. when a male is placed in witha group of inactive virgin females the latterimmediately become active and move fairlydirectly towards the male. Hermann (1971)mentions male calling in M. chalybii (= M.australica). It was noticed in my colonies of M.australica that males walk about with their scapesraised laterally and flagellar segments extended sothat the tip of the scape groove was open. Theyalso stand around in this pose. It could be thatthey are exposing their scape gland to attractfemales. The rearing jars are much larger than thehost cell or puparium and it is difficult to imaginethe need for such a system in the confines of ahost cocoon or puparium.

The distribution of multiporous plate sensillavaries in males. In the hawaiiensis and assemigroups they occur on the club segments only, butin the acasta group they occur on all flagellarsegments. During courtship M. australica femaleswere noticed to open their mandibles. Initially Ithought this to be the signal for the female'sreadiness to copulate thus inducing the male'sfinale. However, van den Assem does not agree(Pers. comm. 1980). Mention has been made

previously of virgin females without malesstanding with open mandibles. When providedwith a dead male pupa females located it andagain stood with open mandibles. It was arguedthat mandibular glands may be the source offemale scent and if this is so then openingmandibles during courtship probably means somechemical input by the female. If. virgin femalescall by mandibular glands then the only olfactoryreceptors in most males are the plate organs andthese would contain the odour specialist olfactorycells. During courtship of species in thehawaiiensis and assemi groups the male positionis such that his clubs are in close proximity to thefemale's mandibles when open. In these groupsonly male club segments bear plate organs.During courtship of the acasta group the maledoes not stand so far forward and his funicularsegments would be in contact with her openmandibles. This is thought to have some bearingon retention of plate organs on the funicle as wellas the club segments in the acasta group males.

ACKNOWLEDGMENTSThis paper is taken from my M.Sc. thesis

submitted to the University of Queensland in1982. My superviser, Dr Elizabeth Exley,University of Queensland, was extremely helpfulin providing constructive comments and editorialremarks. Dr T. Woodward, University ofQueensland and Dr G. Gordh, University ofCalifornia, Riverside, as examiners providedcorrections and advice towards publication of thethesis.

Plates 5b-d, 6a-d, 8a-c were provided by Mr J.Hardy, Electron Microscope Department,University of Queensland and Plates 2a-b, 3a,4b-c were provided by Dr R. Raven, QueenslandMuseum. Sections of the male scape of Melittobiaaustralica (Plates 3b-c) were cut by Mr N. Hall,Queensland Museum and photographed by Dr L.Cannon, Queensland Museum. My technician,Miss Gudrun Sarnes, was of great help checkingmanuscripts and numbering plates. The typistswhose patience I have tried severely were Miss P.Tinniswood and Miss E. Proberts of theQueensland Museum. My wife Judith providedassistance with manuscript checking and plateassembly.

Special thanks are due to Dr J. van den Assem,University of Leiden, Holland. We havecorresponded freely since 1974 and he has been ofthe greatest assistance with notes from hisethological studies on Melittobia.


LITERATURE CITEDASSEM, J. VAN DEN and F.A. PUTTERS, 1980.

Patterns of sound produced by courtingchalcidoid males and its biologicalsignificance. Entomologia exp. app!. 27:293-302.

H.A.J. IN DEN BoscH and E. PROOY, 1982.Melittobia courtship behaviour: acomparative study of the evolution of adisplay. Neth. J. Zoo!. 32: 427-71.

BARLIN, M.R. and S.B. VINSON, 1981.Multiporous plate sensilla in the antennae ofthe Chalcidoidea (Hymenoptera). J. InsectPhysiol. and Embryo!. 10: 29-42.

BOOTH, C.O., 1963. Photokinetic function ofaphid antennae. Nature, Lond. 197: 265-6.

DAHMS, E.C., 1983a. Revision of the genusMelittobia (Hymenoptera : Eulophidae) withthe description of seven new species. Mem.Qd Mus. 21: 241-306.

1983b. A review of the biology of species in thegenus Melittobia (HymenopteraEulophidae) with interpretations andadditions using observations on Melittobiaaustralica. Mem. Qd Mus. 21: 307-30.

GooDPAsTuRE, C., 1975. Comparative courtshipbehaviour and karyology inMonodontomerus (Hymenoptera : Tory-midae). Ann. ent. Soc. Am. 68: 391-7.

GORDH, G. and P. DE BACH, 1978. Courtshipbehaviour in the Aphytis lignanensis group,its potential usefulness in taxonomy, and areview of sexual ibehaviour in the parasiticHymenoptera (Chalcidoidea : Aphelinidae).Hilgardia 46: 37-75.

HERMANN, L.D., 1971. The mating behaviour ofMelittobia chalybii (HymenopteraEulophidae). Unpublished Thesis, Univ.Georgia, U.S.A., 1971, 52 pp.

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and D. SCHNEIDER, 1963. Elektrophysio-logischer Nachweis der Riechfunktion von

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1922. The auditory sense of the honey bee. J.Comp. Neurol. Psych. 34: 173-99.

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PLATE 1Melittobia australica male scape, AgNO, stain, Euparal slide

mount, x 900a) Lateral view.b) Ventral view.


Plate 1

a

b


PLATE 2Melittobia australica male scape.

a) Dorsal view, NaOH cleared, Euparal slide mount,x 340.

b) Ventral view, showing transverse arm of gland,SEM, x 340.

c) Cuticular surface over gland, SEM, x 2,000.

Plate 2

a

b

C



PLATE 3Melittobia australica male scape.

a) Cuticular surface over gland showing pores, SEM,x 5,200.

b) TS male scape just proximal of scape attachment —section through transverse arm of gland, Euparalslide mount, x 650.

c) TS more proximal region of scape-section throughlongitudinal area of gland, Euparal slide mount, x700.


Plate 3

a

b


PLATE 4

Melittobia australica male scape and setae on legs.a) TS longitudinal area of scape showing cuticular

invaginations to support gland, Euparal slidemount, x 2,000.

b) Dense setal tuft on ventral fore-trochanters, SEM,x 1,000.

c) Seta in mid-femoral fringe, SEM, x 4,000.


Plate 4

a

C


PLATE 5Melittobia austratica male, female antennae.

a) Male club, AgNO, stain, Euparal slide mount.b) Female club, SEM, x 900.

i) long thin unfluted setae.ii) tapering fluted seta.iii) multiporous plate sensillum.iv) short basiconic capitate peg.

c) Male club, segments 2 and 3, SEM, x 2,000.d) Male tapering fluted setae, SEM, x 2,800.


Plate 5


PLATE 6Melittobia australica male flagellum and female sensillae.

a) Male flagellum, SEM, x 600.b) Distal female club after exposure to ethyl acetate,

SEM, x 1,300.c) Multiporous plate sensillum of freshly moulted

female after exposure to ethyl acetate, SEM, x10,000.

d) Multiporous plate sensillum of older female afterexposure to ethyl acetate, SEM, x 5,500.

Plate 6‘


a^b

C


PLATE 7

Melittobia australica female short basiconic capitate pegs.a) Older female killed by immersion in ethyl alchol,

SEM, x 13,000.b-d)Freshly moulted female after exposure to ethyl

acetate, SEM, (b x 10,000; c x 18,000; d x13,000).

a


Plate 7


PLATE 8

Grasshoper basiconic pegs.a) Freshly moulted Atractamorpha similis, SEM, x

6,000.b) Freshly moulted Atractamorpha similis, SEM, x

21,000.c) Several hours after moulting Valanga irregularis,

SEM, x 7,500.


Plate 8

a^b

C

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