The biology and taxonomy of Vanhornia eucnemidarum Crawford, a rare and specialized parasitoid of Eucnemidae, is reviewed. The position of the genus Vanhornia as a separate family is reaffirmed

Deyrup, Mark

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Mark Deyrup

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Notes on the Vanhorniidae (Hymenoptera)

Valparaiso University

The Great Lakes Entomologist Volume 18 Number 2 - Summer 1985 Number 2 - Summer 1985 Article 2 June 1985 Notes on the Vanhorniidae (Hymenoptera) Mark Deyrup Archbold Biological Station Follow this and additional works at: https://scholar.valpo.edu/tgle  Part of the Entomology Commons Recommended Citation Deyrup, Mark 1985. "Notes on the Vanhorniidae (Hymenoptera)," The Great Lakes Entomologist, vol 18 (2) Available at: https://scholar.valpo.edu/tgle/vol18/iss2/2 This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. NOTES ON THE VANHORNIIDAE (HYMENOPTERA) Mark Deyrupl ABSTRACT The biology and taxonomy of Vanhornia eucnemidarum Crawford, a rare and special­ized parasitoid of Eucnemidae, is reviewed. The position of the genus Vanhornia as a separate family is reaffirmed. The family Vanhorniidae is one of the most obscure families of North American insects. The single genus includes only two species: Vanhornia eucnemidarum Crawford (1909), found in eastern North America, and V. teileri Hedqvist (1976), known only from Sweden. J estimate that fewer than 50 specimens of Vanhorniidae have been collected, though both species live in areas blessed with relatively large numbers of resident entomologists. The scarcity of specimens is probably due partly to the genuine rarity of the species and partly to their elusive habits; living specimens that I have observed practiced a combination of short flights and rapid runs (like some pompilids) that was frustrating to both net and fingers. Since the host of V. eucnemidarum, the eucnemid beetle. is of no economic importance, there is no practical need to study its rare parasitoid. Nonetheless, V. ucnemidarum is of great interest because it is one of our most peculiar Hymenoptera. The purpose of this note is to summarize the scattered information on V. eucnemidarum and contribute a few original observations. \'anhomia eucnemidarum is known from Quebec west to Michigan and south to Georgia and Kentucky (Townes and Townes 1981), The type series was collected from "cells oflarvae of the family Eucnemidae" by Van Horn at Silver Springs, Maryland, and one specimen collected on Plummer's Island, Maryland (Crawford 1909). Specimens have been reared from I sorhipis ruficornis (Say) (Champlain 1922, Brues 1927). My specimens are from Tippecanoe County, Indiana. Ten specimens, eight females and two males, were collected in June and July from a Malaise trap set up in a small wooded ravine. Two specimens. one male and one female, emerged I May 1981 from pupal cells of I orhipis rujicornis in a dead sapling ofAcer saccharum Marsh, brought indoors 2 April 1981. The complete larval skin of the host was found in the cell from which the male parasitoid emerged. The pupal cell had undoubtedly been constructed by the eucnemid, and was identical to those from which specimens of I. ruficornis emerged. There was no cocoon or visible lining in the cell. The male and female when placed together in a plastic container showed no interest in each other, but spent their time running back and forth over the sticks provided, The female showed ovipositing behavior as described below. The female liyed for five days, the male four. In addition to these specimens, I have seen three specimens on dead beech and maple in dense forest in June 1981. From a ta.'{onornlc standpoint it is fortunate that the venation of V. eucnemidarum clearly links it to the superfamily Proctotrupoidea, as this insect is otherwise apparently a mass of specialized character states. The most distinctive of these are the swollen temples: the exodont mandibles; the low attachment of the antennae; the prothoracic "neck;" the concave mesopleuron; the deeply pitted thorax; the long, fine, flexible, exserted ovipositor; the fused gastral tergites 1--4; the keeled and abruptly deflexed 5th IArchbold Biological Station, P.O. Box 2057, Lake Placid, FL 33852. 1Deyrup: Notes on the Vanhorniidae (Hymenoptera)Published by ValpoScholar, 1985------------_ ..... _ .. _ .. 66 THE GREAT LAKES ENTOMOLOGIST Vol. 18, No.2 gastral tergite; and the grooved gastral sternites (Figs. 1--4). Mason (1983) has shown that gastral tergites 6-8 are much reduced and telescoped into the abdomen. Behaviorally V. eucnemidarum differs from representative proctotrupoids I have observed (Proctotrupidae, Scelionidae, Heloridae) in its running-and-flying locomotion and in the rapid up and down movements of the gaster. The ovipositor of Vanhornia is one of its most interesting features. When not in use it is bent forward at the base so as to lie in a groove along the ventral side ofthe gaster (Fig. 4). This groove is not nearly long enough to accommodate the ovipositor, which is about the same length as the entire insect, and the tip of the ovipositor curves up at the base of the gaster to lie between the wings (Fig. 1). This can be seen in some dead specimens and was also observed in the live female that emerged in the laboratory. The ovipositor is probably held in place by projections on the propodeum and the first gastral segment (Fig. 4), but this mechanism was not clearly seen in the living specimen as the gaster was in constant movement. The ovipositor is 5.8 mm long and extraordinarily thin, about 0.05 mm. In spite of its slenderness, the ovipositor consists f the usual four valvulae, the outer two blunt and equipped with hairs, the inner two ending in stylets. Two apparent oviposition attempts were observed, during which the ovipositor was at a right angle to the body (Fig. 4) while its tip probed the cracks of the broken end of a stick containing eucnemids. The tip of the ovipositor is highly flexible, and its delicate probing resembled that of t e tip of a moth's proboscis seeking nectar. Townes and Townes (1981) reported an observation f the ovipositor being passed along a crack in a hardwood log. The functional morphology of the ovipositor is unknown, but it is probably not used in the same way as the long, wood-drilling ovipositor of certain Ichneumonidae and Braconidae. In these ichneumonoids the ovipositor is stiff and springy, and the pressure of the limber ovipositor against the wood appears (in my observations) to help drive the ovipositor into the wood. During drilling the ichneumonoid sheath splits to free the \\\\ I'\\ Ii I:I ,; !2 4 Figs. 1-4.(1)Female Vanhornia eucnemidarum, actual length 5.8 mm; (2) frontal view of head of female; (3) Base of ovipositor during oviposition attempt; (4) ventral view of gaster of female. 2The Great Lakes Entomologist, Vol. 18, No. 2 [1985], Art. 2https://scholar.valpo.edu/tgle/vol18/iss2/21985 THE GREAT LAKES ENTOMOLOGIST 67 ovifK)sitor partially or entirely. In V. eucnemidarum the ovipositor is highly flexible. By use of a rninuten pin the sheath can be split and the ovipositor extracted, but it is not known that the sheath separates during oviposition. A female immobilized (with a bit of modelling clay) on a microscope slide was able to repeatedly thrust the ovipositor a short way out of the tip of the sheath without separating the sheath. Mason's drawing (1983) of the ovifK)sitor gives some idea of how this might be controlled by sliding the first valvifer inside the second. The structure of the ovipositor and the observed behavior of females suggest that the host is attacked when it is an egg or a young larva that has not tunneled far into the wood. I. rujicomis itself has a long tubular ovipositor with which it inserts eggs deep into crevices of dead wood. If the egg is the stage attacked and the parasitoid has a long period before it begins to develop in the host, this would constitute a biological difference between the Vanhomiidae and the Proctotrupidae. If the host s attacked only a  an egg or newly hatched larva, the brevity of opportunity provided for the parasitoid, combined 'With the concealment of the host, might help explain the rarity of V. eucnemidarum. The other most notable feature of Vanhornia is the exodont mandibles (Fig. 2). Exodont mandibles are not common in insects, occurring in Vanhornia, in braconids of the subfamily Alysiinae, and in some larval Eucnemidae, including I. ruficornis. Van Hom (1909) described the action of the mandibles of M lasis pectinicornis Melscheimer as saw-like, appropriate for the slit-like galleries that the larvae construct. Adult eucnemids which, like Vanhornia, n ed only escape from the pupal chamber, have normal mandi­bles. The adaptive significance of the exodont mandibles of Vanhornia therefore remains unknown, and it is difficult to connect these unusual mouthparts with those of the host unless one assumes that Vanhornia is descended from much flatter ancestors that completed their development in the larval galleries rather than the pupal cell of their host. The Vanhomiidae appear to be a highly specialized offshoot of the primitive Procto­trufK)idea. The most impressive proctotrupoid character of Vanhornia is the overall wing yenation, which is strikingly similar to that of Helorus paradoxus (Provancher), though Helorus differs in having a distinctive detached CuA2 vein in the forewing. The venation of Vanhornia also resembles that of Ropronia, though the medial (first discoidal) cell of Ropronia is not triangular as it is in Vanhornia. These similarities in the venation of the Vanhorniidae, Roproniidae, and Heloridae apparently led Riek (1955) to combine all three families, along the with Monomachidae, in the family Heloridae. Vanhornia fails to fit into Riek's expanded definition of the Heloridae because Vanhornia has one-segmented trochanters and the antennae are situated low on the face, almost adjacent to the clypeus. More recently, Townes and Townes (1981) included Vanhornia in the family Procto­trupidae. The many distinctive features of Vanhornia are apparently interpreted as specialized, derived character states superimposed on a proctotrupid base. When these features are discounted, however, there are no morphological character states left that are shared only with the Proctotrupidae. The use of beetle larvae as hosts is a biological characteristic of Vanhornia shared only with the Proctotrupidae (if the Pelecinidae are excluded from the Proctotrupoidea), but this does not seem to be a strong link, especially if the method of parasitization is different. It is easy to feel an intuitive reluctance toward placing an extraordinarily specialized organism in its own family, an action that usually implies the organism is not only specialized but also ancient. There is a tendency to feel that specialization is ultimately unadaptiye in a changeable world, but in some instances specialization may be a refuge. It is difficult to avoid the impression that a number of small, highly specialized families of Hymenoptera. such as the Vanhomiidae, Heloridae, Roprioniidae, Austroniidae, Pelecinidae. Eyaniidae, and Aulacidae, are remnants that have held out against the evolutionarily aggressive ichneumonoids by a kind of entrenched specialization. Thanks to he work of Crawford (1909), Townes and Townes (1981), and Mason (1983). the morphology f V. eucnemidarum is known in some detail, but a number of questions remain about the biology of this species. These questions deal with the function of the oyifK)sitor and the mandibles, the general life history, and the position of the parasitoid pupa v.ith respect to that f the dead host larva. 3Deyrup: Notes on the Vanhorniidae (Hymenoptera)Published by ValpoScholar, 198568 THE GREAT LAKES ENTOMOLOGIST Vol. 18, No.2 As a final enigma, a poignant historical oddity is associated with the Vanhomiidae. The type series was reared from eucnemids by R. W. Van Horn, a preparator working for A. D. Hopkins in the Bureau of Entomology. Van Horn developed an independent interest in larvae of Eucnemidae, and made a number of original observations which were published late in 1909. Among the comments of A. D. Hopkins appended to Van Horn's paper is the stat ment that on 9 February 1909, Van Horn set off for the local laundry with a bundle of washing under his arm and was never seen again. Were it not for this unfortunate disappearance we would undoubtedly know a great deal more about the biology of the eucnemids and their parasitoids; we have not progressed very impressively since 1909. LITERATURE CITED Brues, C. T. 1927. Observations on wood-boring insects, their parasites and other associated insects. Psyche 34:73-90. Champlain, A. B. 1922. Records of hymenopterous parasites in Pennsylvania. Psyche 29:95-100. Crawford, J. C. 1909. A new family of parasitic Hymenoptera. Proc. EntomoL Soc. Washington 11:63-64. Hedqvist, K. -j. 1976. Vanhornia leileri n. sp. from central Sweden (Hymenoptera: Proctotrupidae, Vanhornlinae). Entomol. Scand. 7:315-316. Mason, W. R. M. 1983. The abdomen f Vanhornia eucnemidarum (Hymenoptera: Proctotrupoidea) Canadian Entomo!. 115:1483-1488. Riek, E. F. 1955. Australian Heloridae, including Monomachidae (Hymenoptera). Aus­tralian J. Zoo!. 3:258-265. Townes, H. K. and M. Townes. 1981. A revision f the Serphidae (Hymenoptera). Mem. Amer. EntomoL Inst. 32:1-207. Van Horn, R. W. 1909. Notes on some of the Eucnemidae of the eastern states. Proc. Entomol. Soc. Washington 11:54-61. 4The Great Lakes Entomologist, Vol. 18, No. 2 [1985], Art. 2https://scholar.valpo.edu/tgle/vol18/iss2/2

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Notes on the Vanhorniidae (Hymenoptera)

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