MIMICRY OF HYMENOPTERAN ANTENNAE BY SYRPHIDAE P.downloads.hindawi.com/journals/psyche/1970/028967.pdf1970] lJ/aldbauer--Mimicry 47 to be geniculate as are the antennae of the models

MIMICRY OF HYMENOPTERAN ANTENNAEBY SYRPHIDAE*

BY G. P. WALDBAUERDepartment o17 Entomology

University of Illinois

Many flies o17 the Family Syrphidae mimic aculeate Hymenoptera.The hymenopterans, particularly vespid wasps, which serve as modelsor these syrphids have relatively long, many segmented, fili17orm an-tennae which are o17ten in motion and are usually a conspicuous17eature. Most syrphids, like all o17 the ot’her cyclorrhaphous Diptera,have three-segmented antennae which are usually short and decidedlyinconspicuous as, 17or example, are those o17 the. non-mimetic Tropidiaquadrat.a (Say) (fig. ). To. human eyes the absence o17 conspicuo.usantennae decreases the resemblance o17 mimic to model, and the effectis presumably the same to at least so.me o17 the species o.17 predatorswhich are to varying degrees deceived by the mimetic resemblance.I have observed in nature several species o17 wasp-mimicking syrphidswhich either have or give the appearance o17 having long, fili17o.rmantennae. In each case the. living mimic is remarkably deceptive andonly close observation reveals that wasp-like antennae are not actuallypresent.The antennae ot7 Sphecomyia vittata (Wiedemann) (fig. 2) and

Ceriana signifera’ (Loew) (fig. 3) have been lengthened. The firstand second segments o17 the antennae of S. vittata are very long whilethe third is .short and bea.rs an arista. The apparent length o17 theantennae is 17urther increased by the 17orward-extending process ofthe head capsule which bears them. In C. signifera the first andthird segments are quite long while the second is o17 only moderatelength. The third segment bears a terminal style rather than anarista, tTurther extending its length. In life both species hold theantennae in positions which suggest the geniculate antennae o17 vespids.The antennae o17 Tenthredomyia abbreviata (Loew) (fig. 4) ap-

pear to. be long because they are borne by a long, 17orvard-extendingprocess of the head capsule. The antennae themselves have been butslightly lengthened. The first segment is moderately long, but thesecond and third are short although the third bears a terminal stylerather than an arista. As in the preceding two species living specimenso17 T. abbreviata hold the antennae in such a. way that they appear

*Manuscript received by the editor January 19, 1970.

45

46 Psyche [March

1970] lJ/aldbauer-- Mimicry 47

to be geniculate as are the antennae of the models. This orientationis retained even in some dried specimens.

Spilomyia hamifera Loew (fig. 5) has antennae which are shortand qlite inconspicuous, similar in length and form to. the. antennaeof non-mimetic Syrphidae (fig. ). They are borne by a tuberclewhich is only slightly produced. In this case the long, dark, filiformantennae of the models are mimicked by the dark front legs whichare held up and waved about in front of the head. The effect isvery realistic and can easily deceive an inexperienced collector. Thetarsi and the distal portion of the tibiae of the front legs are dark.The proximal portion of the front legs as well as the other twopairs of legs are yellow as are those of the models. I have observedthis behavior in S. kamifera both while they were feeding on flowersor resting on foliage. Occasionally, all six legs are on the substrate,the usual position for most syrphids. I do not know in what positionthe legs are held in flight.

I have oh.served a similar use of the front legs in three othervespid-mimicking Spilomyia, S. fusca Loew, S. longicornis Loew andS. quadrifasciata (Say). In each of these species the front tarsi anda part of the front tibiae are dark. The remaining legs are yellowexcept for dark areas on the femora of S. fusca and S. quadrifasciata.The legs of S. crandalli Curran and .S. foxleei Vockeroth are similarto those of the last two .species mentioned although the meso- andmetatarsi of S. foxleei are somewhat darkened distally. S. ka’hli Snowdoes not have the front legs darkened. I have seen only pinned speci-mens of the last three species.. It may be that S. kahli does not usethe t?ront legs to mimic antennae, but it .seems more likely that modelswith yellow antennae will be found to occur within its range in thesouthwestern United States. Curran I951 stated that all speciesof Spilomyia rest on the ]?our posterior legs and use the front legsto mimic antennae.At least some of the North American species of Temnostoma use

the front legs in the same. manner. In nature I have seen this doneby T. balyras Walker, T. pictulum Williston and T. trifasciatumRobertson. In each of these species the front legs are dark while theother two pairs are largely yellow. Although I have. not seen them

Figs. 1-5. Dorsal and lateral views of the heads of five species ofSyrphidae.

Fig. 1. Trotida quadra,ta (Say). Fig. 2. Slhecomyia ittata (Wiede-mann). Fig. 3. Ceriana signifera (Loew). Fig. 4. Tenthredomya abbre-iata (Loew). Fig. 5. Stilomyia hamifera Loew.

Psyche [March

in life I have examined dried specimens of T. alternans Loew and T.vesliforme (L.) and found the legs to be similarly marked.

These observations show that in the Family Syrphidae there areat least four ways of achieving the appearance of aculeate antennae.These tour ways represent at least three and perhaps four independentevolutionary innovations. Silomyia and Sphecomyia certainly presentevolutionarily independent solutions to the problem of mimickinghymenopteran antennae. Ceriana and Tentkredomyia represent atleast a third line and may have evolved solutions independently ofeach other. The antennae of both are stylate and otherwise similar.The antennae of Tentkredomyia are borne by a long process, butCeriana exhibits a similar though very short process. Thus it ispossible that these two. genera present primitive and advanced ver-sions of the same evolutionary line rather than two. separate lines.The. question cannot be decided on the basis of the present evidence.

Nicholson (9a7) noted that among the Syrphidae long antennaeare generally associated with those species in which the over-allmimetic resemblance to. Hymenoptera is the most highly developed.My observa.tions of living Syrphidae in the eastern United Statesconfirm this view. I have seen very ew non-mimetic syrphids whichhave or appear to have long antennae. In life the species mentionedabove are remarkably vespid-like both in general appearance and be-havior. However, they are not necessarily preci,se mimics of a par-ticular species of vespid. I would, nevertheless, consider tem to bespecialized mimics which exhibit a number of different adaptationswhich imitate salient features of vespids. For example, of the fourmimetic species illustrated, all have a more or less distinct dark areaalong the leading edge of the wing, suggesting the dark band pro-duced by the longitudinal folding of the vespid wing at rest. Thefour species illustrated also. have either a constriction at the baseof the abdomen or markings which suggest such a constriction.

It is notevorthy that stylate antennae occur in only three of the88 genera (Ceriana, Tenthredomyia and Callicera) and 7 of the939 species of North American Syrphidae listed by Wirth et al.(x965). The genera Ceriana and Tenthredomyia include thirteenspecies which occur in America north of Mexico. All are waspmimics. There are four species of Callicera in the same area. Theone species which I have seen is not a wasp mimic and is probablynot mimetic at all.

In nay experience syrphids which mimic bees neither have nor givethe appearance of having long antennae. From observations of living

1970] H/’aldbauer Mimicry 49

insects in the field I have found this to be true of Mallota bautius(Walker), M. posticata (Fab.), Eristalis bard,us (Say) and E.bastardii Macquart, all of which mimic bumblebees. It is also trueof Eristalis’ tenax (L.) which is requently cited as a mimic of thehoneybee. Another bumblebee mimic, Kolucella bombylans (L.),has a. rather long and feathery arista which is somewhat conspicuousin the field, but does not suggest to me the antenna of a bumblebee.It would be interesting to. know if it is a valid generalization thatbee-mimicking syrphids do not appear to have long antennae and, ifso, to attempt to discover why this is the case.

zlcknowle’dgment: Thanks are due to. Mrs. Alice Prickett whomade the drawings.

REFERENCES CITEDCURIA, C. H.

1951. Synopsis of the North American species of Spilomyia (Syrphidae,Diptera). Amer. Mus. Nat. Hist., Amer. Mus. Novitates 1492:1-11.

NICHOLSON, A. J.1927. A new theory of mimicry in insects. Austr. Zool. Sydney "10’-10 + 1 pls.

WlRTI-I..W.W. Y. S. SEDMAN’ AND. n. V. WEEMS JR.1965. Family Syrphidae. p. 557-625. In A. Stone, C. W. Sabrosky,

W. W. Wirth, R. H. Foote and J. R. Coulson led.I, A Catalogof the Diptera of America North of Mexico. U.S.D.A., Agrie.Handbook no. 276.

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MIMICRY OF HYMENOPTERAN ANTENNAE BY SYRPHIDAE P.downloads.hindawi.com/journals/psyche/1970/028967.pdf1970] lJ/aldbauer--Mimicry 47 to be geniculate as are the antennae of the models