INFLUENCE OF THERMOPERIOD AND PHOTOPERIOD ON REPRODUCTIVE DIAPAUSE IN BRUCHIDIUS-ATROLINEATUS (PIC) (COLEOPTERA, BRUCHIDAE)

Bruchidius atrolineatus (Pic) is a common pest infesting cowpea seeds (Vigna unguiculata Walp) in Africa. In the Sahelian zone, the adults are in reproductive diapause during the dry season. Diapause induction depends on the climatic conditions during embryonic and post-embryonic development. A strain of B. atrolineatus originating from the Niamey (13-degrees-N) was reared in different thermoperiodic and photoperiodic conditions. In the thermoperiodic regime 40:25-degrees-C, in continuous darkness, induction of diapause was dependent on the duration of the thermophase. Photoperiod could also influence diapause induction but the response depended on the temperature. When the beetles were reared in conditions of LD 12:12 h, 40:25-degrees-C, for seven generations, the proportion of diapausing adults decreased and their sensitivity to photoperiod increased. In LD 14:10 h, 40:25-degrees-C, the proportion of diapausing adults remained high regardless of the photoperiod. In these conditions, the first emerging adults were sexually active and were used for selection of a strain with a low incidence of diapause. After twelve generations, the proportion of diapausing beetles was lower than 5%. The responses of this selected strain to photo- and thermoperiods were reduced. The sensitivity of B. atrolineatus to photoperiod and thermoperiod could be controlled by genetic systems as observed in other insect species.