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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.

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Social insects show a variety of temperature-guided behaviors. Depending on whether heat reaches the sensillum via air movements (convective heat) or as radiant heat, specific adaptations of thermo-sensitive sensilla are expected. In the present study the morphology and the physiology of thermo-sensitive peg-in-pit sensilla (S. coeloconica) of the leaf-cutting ant Atta vollenweideri were investigated. S. coeloconica are located predominantly in a single cluster on the apical antennomere, and connect to the outside through a small aperture. The sensory peg is double-walled, embedded in a chamber and innervated by three unbranched dendrites. Using tungsten electrodes, activity of the sensory neurons was measured. In most cases, the neuron with the largest spike amplitude responds to changes in air temperature (convective heat) as well as to radiant heat. In response to a drop in air temperature, the neuron shows a phasic-tonic response followed by a complete adaptation within 1 min (cold-sensitive neuron). Based on their morphology and physiology, it is suggested that the S. coeloconica are involved in the recently described thermal orientation behavior of A. vollenweideri leaf-cutting ants.