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

Bruchidius atrolineatus (Pic) (Coleoptera: Bruchidae) is a beetle deve loping in the seeds of cowpea (Vigna unguiculata Walp) in the Niamey r egion 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 vitell ogenesis began. B. atrolineatus is a short-day species and photoperiod s of 13:13 h or 12:12 h LD are required to terminate diapause. Relativ e humidity has an important role in diapause termination. The beetles remained in reproductive diapause regardless of the photoperiod when t he relative humidity was lower than 40% (8-9 g of water per kg air). F or males, changes in photoperiod and relative humidity were enough to terminate the diapause. For females, the presence of pods or infloresc ences of cowpea was required. Certain specific allelochemical compound s of the host-plant organs are enough to terminate female diapause by a neurosensory pathway or by a trophic action. The regulation of diapa use in B. atrolineatus by various climatic and host-plant factors is i mportant in this species, which has a large distribution area in tropi cal Africa.