PATTERNS IN MALE MATING STRATEGIES OF THE RHYSSINI - A HOLOPHYLETIC GROUP OF PARASITOID WASPS (HYMENOPTERA, ICHNEUMONIDAE)

Three different male mating systems were identified in the ichneumonid tribe, the Rhyssini: an 'after-emergence scramble competition' system; a 'before-emergence scramble competition' system; and a 'before-emergence female defence' system. A morphometric analysis of intraspecific differences in male gaster shape showed that species with before-emergence scramble competition systems apparently show an allometric change in gaster shape with size (smaller males having stouter gasters), while species with either of the other two systems show no such change. This finding and other morphological data enabled mating systems to be predicted in species where it is unknown. In addition, a pooled plot of all specimens (combining intra- and interspecific effects) showed that rhyssine males seem to be built on one of two general plans, showing either an isometric or an allometric change in gaster shape (towards thinner gasters) with increased body size. These differences were correlated with mating systems. The three mating systems appear to be localized in three separate holophyletic groups within the Rhyssini. Some of the variation in mating systems may be explained by consideration of differences between tropical and temperate ecosystems. In temperate regions high host tree densities and seasonal peaks in adult numbers may result in a large number of intruder males and to scramble competition for females. In tropical regions the opposite factors might be expected to lead to a female defence system. The distribution of allometric and isometric species in the tropical and temperate regions only partly supports this hypothesis. It is argued that historical factors may have been as important in the evolution of these systems as ecological ones. © 1991 The Association for the Study of Animal Behaviour.