[Gonotrophic dissociation in Culex pipiens pipiens L. (author's transl)].

Under certain conditions gonotrophic dissociation has been observed in Culex pipiens pipiens. To contribute to a better understanding of the factors which govern the appearance of this phenomenon and of its ecological importance a population in Northern Germany has been investigated. Follicular development, feeding activity and occurrence of gonotrophic dissociation were examined in females obtained from wild-caught larval stages and kept under outdoor conditions after emergence in July and August. In addition overwintering females collected in cellars in September and October were investigated after reactivation by exposure to 16 hours illumination periods and 28 degrees C. In females emerging in August the follicles were generally small, the feeding activity was very low but the rate of gonotrophic dissociation appeared to be higher than that in mosquitoes which had emerged in July. Overwintering females had small follicles and did not take a blood meal during the first days under reactivation conditions. Only after five days a development of follicles and an increase in feeding activity became apparent. Through the effect of long illumination and high temperature the state of diapause was gradually overcome and the females were fully reactivated. At the same time the rate of gonotrophic dissociation in fed females which was high in the early time of exposure to reactivation conditions became low. This suggests that gonotrophic dissociation occurs commonly in females with low feeding activity, i.e. those which are not reactivated completely. In Northern Germany the overwintering females are unfed and nulliparous and gonotrophic dissociation does not seem to play an important role for the overwintering of the mosquito in this area.