Male Courtship Patterns and Female Receptivity Signal of Pteromalinae (Hym., Pteromalidae), With a Consideration of Some Evolutionary Trends and a Comment On the Taxonomic Position of Pachycrepoideus Vindemiae
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Courtship behaviour of a number of species of Pteromalinae (Hym., Pteromalidae) was observed (species are listed in Table I). This paper is a preliminary report about the general properties of courtship in this group of chalcids. Pteromaline males court from a frontal position on the female, the male's front feet being placed on the female's head capsule. The male's courtship repertoire is species-characteristic and presents a number of features that can be used for species recognition (in some cases, e.g. Muscidifurax species, behaviour characters are more easily used than morphological ones in species recognition). Movements with abdomen, wings, mid legs, front legs, antennae, head and mouth parts may be involved in the male's repertoire. Some of these motor coordinations are very ritualised, others do not differ from the presumed originals. Some suggestions are made on the origin of the ritualised components of the displays. The relative importance of the components that are involved in courtship sequences seems to differ between species; a comparison of repertoires leads to the conclusion that there has been a shift of emphasis from more caudally towards more frontally located attributes. This trend is not restricted to within the Pteromalinae but probably affects the Pteromalidae (if not the Chalcidoidea) as a whole. In more primitive groups the courtship position is rather caudal, in other groups the position is more to the front. The extremely frontal position of the Pteromalinae may be the result of a development in evolution towards a more effective communication between partners. Presumably, communication that takes place closer to the sites of greatest sensitivity (head and front tarsi, where many sense organs are located) is more effective (less ambiguous) than communication over greater distances. Courting at the front, however, involves some risk for the male because in crowded situations it was observed that rivals sometimes copulated before the male that performed the courtship sequence was able to do so. Females that have been inseminated are unsusceptible to male courtship stimuli, irrespective the duration of the courtship period. Virgin females are potentially receptive and may be induced into overt receptivity by a sequence of conspecific courtship. A receptive female raises her abdomen to expose her genital aperture, a necessary introduction to a successful copulation. In such groups where the male courts in a caudal position, the raising movement itself seems to be a sufficient signal to the courting male to stop his performance and switch over to copulation. Where the male courts in a frontal position, however, as is the case in the Pteromalinae, his abdomen may not extend far enough to detect the raising movement of the female's abdomen. This is especially so in many species with a distinct sexual dimorphism in body size (in many Pteromalinae the male is considerably smaller than the female). In these groups a secondary signal is produced by the female with her antennae at the moment she comes to accept the courting male for a mate: the flagella are tightly drawn to the head capsule at the moment of raising abdomen. Upon this signal the male backs up and starts copulating. The possible origin of the female signal is discussed. In other chalcid families parallel developments in courtship may be found; especially the Eulophidae seem to offer extremely interesting material for comparative research. The ready-to-copulate signal of female eulophids is the complete reverse of the signal of pteromalines. Some examples are given to illustrate this point. A few taxonomic points are raised. There have been some difficulty to delimitate the Pteromalinae from related groups on morphological evidence alone. Some ethological characters are presented which may profitably be used to delimitate the major part of the Pteromalinae from other groups. Courtship of the species Pachycrepoideus vindemiae (and probably allied species) was found to differ to such extent from the common pattern that it is suggested to place them with some other pteromalid group.