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We focus on the causal organization of courtship behaviour of an insect, i.c. that of the pteromalid wasp Nasonia vitripennis, a parasite of the pupae of various flies. We observe uninterrupted displays of male Nasonia, and analyse temporal structures in order to infer causal relations between display elements. These relations are put to a test by manipulations: displays are interrupted at pre-defined points, or re-started after pauses of various durations, or specific motor patterns are prevented from being executed. The results are summarized in Fig. 13, in which we outline the structure of the underlying organization. The main conclusion is that the performance of courtship is a self-inhibiting process in which head-nodding behaviour (a component of the display) appears to play a key role. Inhibitive effects deteriorate during pauses in between displays (in a non-linear way), but also - albeit less extensively - in periods of non-nodding, during the display itself. We discuss the issue of similar or different principles of organization in courtship behaviour of insects and vertebrates. Although a common basis cannot be excluded, we have to leave open a more definite conclusion for the time being.

In the Chalcidoidea (small hymenopterous parasites of the developmental stages of many kinds of insects) two evolutionary trends can be traced: reduction of male size, and switch of the courtship position of the male relative to the female from rear to front. The positional shift is related to the development of antennal movements produced by the female at the onset of sexual receptivity. The signal function of these movements was shown with experiments including the use of dummies. The experimental results are discussed in relation to selective pressures shaping courtship and mating behaviour in the Chalcidoidea.

Courting males of the parasitic wasp Nasonia vitripennis appear to release a pheromone with the extrusion of mouth parts during so-called head-nodding behaviour. This pheromone provokes sexual receptivity in conspecific virgin Q $. Abdomectomized c~ c~ court readily but have lost the ability to induce receptivity. Head nodding, mouth-part extrusion, and presumably also pheromone discharge, are absent from their courtship behaviour. However, plugging the injury results in reappearance of these motor patterns, and restores courtship success to the level of intact controls. We present some evidence for a hydraulic system involved in pheromone discharge (with head nodding and mouth-part extrusion). At the same time we present evidence, based on comparative data, that this system is unlikely to be a simple "on-and-off" type behaviour.