Distal leg morphology, subgenual organs and host detection in Stephanidae (Insecta, Hymenoptera)

Abstract

The morphology of the tibia and tarsus of all legs is examined in species of two genera of Stephanidae. The subgenual organ (SGO) is examined in more detail for Megischus spp. The fore leg is the most modified in Schlettererius. In Megischus, the SGO of the hind leg is displaced to the middle of the tibia, which is swollen distad of it; in the female the hind tarsi are three-segmented, the basitarsomere being a composite of tarsomeres 1-3. Internally, the SGO of Megischus is suspended between a spine and a ridge. In the mid and hind legs, part of the tibial wall is thinner in the region of the SGO. Our observations provide circumstantial evidence that female Stephanidae detect substrate-borne vibrations when searching for hosts. The absence of antennal modification, as well as information on host stage targeted and general behaviour on the oviposition site indicates that they rely on noise made by the host rather than generate vibrations themselves, in contrast to Orussidae, a parasitoid wasp taxon that has been inferred to employ vibrational sounding. The external receptor elements -membranous pads versus tufts of setae -are not homologous in Orussidae and Stephanidae. A spine and ridge suspensorium of the SGO found in members of both families may represent a derived groundplan feature of the orussid-apocritan clade, with secondary modification or reduction in the latter group. Characters of the distal leg elements and the SGO suggest a basal position of Schlettererius and Stephanus within Stephanidae. Modifications of the hind tibia and tarsus in more derived members of the family indicate a shift in relative importance in vibration detection from the fore leg to the hind leg within the family.

Acoustic communication in the Mountain Pine Beetle, Dendroctonus ponderosae Hopk. (Coleoptera: Scolytidae) : characterization of signals and anatomy

“…Dendroctonus antennae are club type, elbowed, and covered in short setae, which have been implicated in chemoreception (Hopkins, 1909;Lyal and King, 1995). examinations of the legs of D. ponderosae, showed no distinct enlargement of the tibia as would be expected in animals possessing a subgenual organ (Vilhelmsen et al, 2008).…”

Functional Morphology and Evolutionary Diversity of Vibration Receptors in Insects

“…For adult tobacco hornworm moths, M. sexta, about 30 neurons are found in the SGO (Kent and Griffin 1990). A large variance occurs within Hymenoptera: The SGO of ants contains 10-40 scolopidia (Howse 1964;Menzel and Tautz 1994), that of the honeybee Apis mellifera around 40 scolopidia (Kilpinen and Storm 1997), and in parasitoid wasps, females of certain species can have 300-400 SGO scolopidia (Vilhelmsen et al 2008). The functional relevance of the SGO structure and cell numbers has only been discussed for the parasitoid wasps (see Sect.…”

“…Scale 100 lm organization of the subgenual organ is of notable diversity (Fig. 14.5): it is club shaped in some Hymenoptera species and in termites (Howse 1964), whereas in other Hymenoptera, the organ hangs in the hemolymph cavity (Vilhelmsen et al 2001(Vilhelmsen et al , 2008. In orthopteroid insects, the SGO is often sail shaped and suspended in the hemolymph (Lin et al 1995;Schnorbus 1971).…”

The Ecology, Behavior, and Biological Control Potential of Hymenopteran Parasitoids of Woodwasps (Hymenoptera: Siricidae) in North America

“…Adults mated frequently in cages, with females mating more than once. Adult females oviposited roughly 2Ð3 wk after emergence, and are believed to detect host vibrations in wood via sensory organs on their tibia and tarsi (Vilhelmsen et al 2008). Adults can reach at least 3.4 cm into the wood with their ovipositor to locate siricid larvae, which are stung and paralyzed before oviposition.…”