Gitta Siekmann

The Sweet Tooth of Adult Parasitoid Cotesia rubecula: Ignoring Hosts for Nectar?

Investing time and energy into survival and reproduction often presents a trade-off to many species of animals. In parasitic wasps, both hosts and sugar sources contribute to the foragers fitness but are often found in different locations. The decision to search for hosts or for food can have a strong impact on fitness when the foragers lifetime is short and resources are not abundant. We investigated the tendency of flowers and hosts to attract 1-day-old female Cotesia rubecula Marshall (Hymenoptera: Braconidae) with different feeding histories in a wind tunnel. Only well-fed wasps exhibited a preference for hosts. In comparison, unfed wasps visited hosts and flowers in equal proportions. Feeding experience had a strong impact on the searching behavior and the number of landings on both resources. Host and food stimuli seem to be equally attractive to hungry parasitic wasps such as C. rubecula. We expect that under field conditions the time available for active food searching in female C. rubecula is short and influenced by the presence of hosts.

A maternal gene mutation correlates with an ovary phenotype in a parthenogenetic wasp population

Endoparasitoid wasps rely on maternal protein secretions, including viruses and virus-like particles (VLPs), to overcome host defense reactions. In the ichneumonid Venturia canescens, VLPs are assembled in the nuclei of ovarian calyx gland cells, secreted into the lumen of the gland, and eventually transmitted into the host caterpillar together with the parasitoid egg. One of the genes coding for VLP proteins, termed VLP1, exists in two alleles producing two structurally different proteins. Here we describe the establishment and initial phenotypic characterisation of two parthenogenetic laboratory strains, which differ in VLP1 as well as in other genetic markers. A comparison of calyx tissues from the two strains revealed morphological differences that seem to affect egg movement from the ovarioles into the oviduct. The observed histological changes are correlated with differences in egg maturation and embryonic development causing a delay in larval hatching in one of the strains. Under conditions that favour superparasitism, the two strains differ in the number of offspring produced.