The Interaction of External and Internal Factors in the Courtship of Parasitic Wasps (Hym., Pteromalidae)

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Abstract
Our topic of interest is the causal organization of courtship and mating behaviour of parasitic wasps (Hymenoptera, Pteromalidae), more especially that of Nasonia vitripennis. Males pursue newly emerged females over a short distance, mount on top, and take up a position at the front, the fore tarsi placed on the female's head. Courtship displays consist of characteristic combinations of motor patterns, which are repeated a variable number of times in so-called courtship cycles. Movements with the wings, head, mouthparts, and antennae are conspicuous components. This applies in particular to head-nodding movements, which occur in series. A female may become sexually receptive while being courted; she signals the onset of this condition with a movement of her antennae. The male will react promptly: he stops courting and backs up into the copulatory position. The signal coincides almost invariably with the first nod of a series; signalling at other times led to a postponement of the backing-up reaction. Because Nasonia males readily court on dummy females, we used a dummy with moveable antennae to investigate the temporal relationship of signal and reaction. We observed two types of postponed backing-up reactions: simple backing up, and backing up after performance of one or more display movements. At the same time, we found a quantitative relationship between durations of the latencies, and the timing of the signal relative to the display. Our investigations produced evidence for endogenous, periodic changes, which take place during the succession of courtship cyles. The postponed backing-up reactions of different types could be explained in terms of interactions between the effects of signalling and the endogenous dynamics of courting males.

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