INTERACTIONS BETWEEN PHOTOPERIOD, RELATIVE-HUMIDITY AND HOST-PLANT CUES ON THE REPRODUCTIVE DIAPAUSE TERMINATION IN BRUCHIDIUS-ATROLINEATUS PIC (COLEOPTERA BRUCHIDAE)

Bruchidius atrolineatus (Pic) (Coleoptera: Bruchidae) is a beetle developing in the seeds of cowpea (Vigna unguiculata Walp) in the Niamey region of Niger (13-degrees-N). Adults of this tropical bruchid undergo a reproductive diapause during the dry season when the pods of their host-plant are unavailable. The reproductive organs of the diapausing beetles were non-functional and two specific diapause proteins appear in the haemolymph at the beginning of the imaginal life of both sexes. These diapause proteins disappear when diapause terminated and vitellogenesis began. B. atrolineatus is a short-day species and photoperiods of 13:13 h or 12:12 h LD are required to terminate diapause. Relative humidity has an important role in diapause termination. The beetles remained in reproductive diapause regardless of the photoperiod when the relative humidity was lower than 40% (8-9 g of water per kg air). For males, changes in photoperiod and relative humidity were enough to terminate the diapause. For females, the presence of pods or inflorescences of cowpea was required. Certain specific allelochemical compounds of the host-plant organs are enough to terminate female diapause by a neurosensory pathway or by a trophic action. The regulation of diapause in B. atrolineatus by various climatic and host-plant factors is important in this species, which has a large distribution area in tropical Africa.