Host location and oviposition in a basal group of parasitic wasps: the subgenual organ, ovipositor apparatus and associated structures in the Orussidae (Hymenoptera, Insecta)

Abstract

Anatomical studies and behavioural observations indicate that representatives of the Orussidae use vibrational sounding to detect suitable oviposition sites. During host location, vibrations generated by tapping the tips of the antennae against the wood are picked up by the fore legs through the basitarsal spurs, transmitted along the basitarsi to thin-walled areas on the tibiae and through haemolymph to the subgenual organs, where they are transduced into nerve impulses. The apical antennomeres are distinctly shaped and have the cuticle thickened distally. The fore basitarsi have weakly sclerotised basitarsal lines proximally and membranous basitarsal spurs distally. The external wall of the fore tibiae have thin-walled areas distally on their posterior parts. Internally, large subgenual organs are situated opposite the thin-walled areas and each organ consists of 300-400 scolopidial units suspended between a lateral cuticular spine, a ventral sheet and a median ridge. The ovipositor is several times the length of the body of the wasp. When at rest, it extends all the way into the prothorax, where it is coiled before extending posteriorly to lie between the third valvulae distally. The ovipositor lies in a membranous ovipositor sac attached posteriorly to the proximal parts of the ovipositor apparatus and the posterior margin of sternum 7. In the ovipositor apparatus, the anterior parts of the second valvifers are displaced and expanded anterodorsally, inverting the first valvifers and the base of the ovipositor. When in use, the ovipositor is extended and retracted by median apodemes situated on the anterior margins of abdominal sterna 3-7. Longitudinal muscles between the apodemes allow the latter to grip the ovipositor in troughs between them. The ovipositor extends from the abdomen at the tip of sternum 7, and an internal trough on sternum 7 serves to guide the ovipositor into the wood. Despite the alterations observed in the ovipositor apparatus in the Orussidae, the musculature is almost complete and the mode of operation presumably not much different from that of other representatives of the Hymenoptera. The different ways parasitic wasps with very long ovipositors handle and accommodate these and the implications for the evolutionary history of Hymenoptera are discussed.

Sting microsculpture in the digger wasp Bembix rostrata (Hymenoptera, Crabronidae)

“…Th e terms used are preferably from Vilhelmsen et al 2001, but also from Quicke et al 1999, Gnatzy and Volknandt 2000and Packer 2003. Th e following abbreviations were used: ap, apical process of inner membranous wall of 3 rd valvula; au, aulax; …”

“…Th ere are numerous classic works on morphology and functions of the hymenopterous ovipositor (e.g., Snodgrass 1956, Oeser 1961, Scudder 1961, Smith 1970, Quicke et al 1999, Vilhelmsen 2000, Vilhelmsen et al 2001, Packer 2003. Several publications dealt especially with microsculptural characters which have been used for phylogenetic reconstructions in some groups, mainly parasitic wasps (e.g., Quicke et al 1992, 1999, Le Ralec et al 1996, Nénon et al 1995, Rahman et al 1998.…”

Morphology and function of the ovipositor mechanism in Ceraphronoidea (Hymenoptera, Apocrita)

“…Despite the extensive descriptive work done on comparative morphology of the Hymenoptera female terminalia (Oeser 1961, Smith 1970, Le Ralec et al 1996, Quicke et al 1992, Quicke et al 1994, Quicke et al 1999, Vilhelmsen 2000, Vilhelmsen et al 2001, the available morphological data on the ceraphronoid female terminalia are restricted to the distal region of the terebra (Quicke et al 1994, Le Ralec et al 1996 and the accessory glands (Höller et al 1993). The skeletomuscular system of ceraphronoid ovipositor remained, until now, relatively unexplored.…”

Do acoustic cues mediate host finding by Syngaster lepidus (Hymenoptera: Braconidae)?

“…Female S. lepidus may detect substrate-borne acoustic signals produced by feeding of their larval hosts by means of a subgenal organ in the tibia as is suspected with vibrational sounding (Vilhelmsen et al 2001). They might also detect near-field airborne sound via the Johnston's organ in the antennae, but it is difficult to distinguish between the substrate vibration and near-field sounds in this experiment.…”