POSTDIAPAUSE SENSORY RESPONSIVENESS IN CULEX-PIPIENS

Adult Culex pipiens females do not host-seek and hence do not feed on blood during diapause. Such diapausing females do not possess the highly sensitive olfactory receptors for the host attractant lactic acid that are characteristic of nondiapausing host-seeking females. In this study single unit electrophysiological recordings coupled with quantitative odour-delivery techniques were employed to study sensory responsiveness in females that had terminated diapause (as evidenced by resumption of ovarian follicle growth). Such females display changes in peripheral receptor responsiveness that can be summarized as follows: (1) Highly sensitive lactic acid-excited cells associated with the sensilla basiconica type A3 are present in females that have terminated diapause. (2) The proportion of responsive (albeit nonspecific) cells associated with the sensilla trichodea type A2 increases whereas the proportion of nonresponsive cells decrease in post-diapause females; this change in sensory responsiveness is not accompanied by an increase in the number of cells specifically sensitive to ethyl propionate or by a change in receptor sensitivity. Resumption of post-diapause anautogenous reproductive activity in this mosquito thus involves resumption of ovarian follicle development, resumption of host-seeking behaviour, and changes in peripheral receptor responsiveness.