Règles de décision de départ des patchs employées par les femelles sexuées et asexuées chez le parasitoïde Venturia canescens: Effet des conditions environnementales.

AMAT, I.; CASTELO, M.K.; BERNSTEIN, C.

Bordeaux, Francia

Congreso; XXXIème Journée des Entomophagistes; 2003

ASAB

Theory predicts that asexual reproduction has a competitive advantage over sexual reproduction because of the two-fold cost of producing males. In the parasitoid Venturia canescens, both thelytokous (asexual) and arrhenotokous (sexual) wasps are known to co-occur in natural conditions. In this parasitoid, thelytoky is obligate and not induced by Wolbachia bacteria. What could be the ecological, short term, factors that favour the coexistence of arrhenotokous and thelytokous populations ? In parasitoids the strategies of hosts exploitation are directly linked to their reproductive success. Differences in efficiency of the adopted strategies, for instance under different conditions, could play a role in the competitive balance opposing both reproductive modes. Both arrhenotokous and thelytokous V. canescens populations are found in natural conditions. Conversely, in anthropic conditions (mills and granaries) populations are exclusively thelytokous. These locations provide a relatively constant environment and an ample supply of hosts. This makes temperature and host availability two pertinent factors in discriminating the two environments. In this work we compared patch time allocation of thelytokous and arrhenotokous females combining different temperatures, and host densities. Surprisingly, arrhenotokous and thelytokous females did not show any difference in the way they discriminate between patches of different richness. Arrhenotokous females are more sensitive to changes in temperature. When foraging at low temperature, they stay longer and exploit patches more thoroughly. These results will be discussed in the context of the dynamics of optimal resource exploitation (e.g. how the environment shapes behaviour by acting on the egg vs. time limitation continuum) and of the maintenance of sexual reproduction.