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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 (13oN) was reared in different thermoperiodic and photoperiodic conditions. In the thermoperiodic regime 40:25oC, 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, 40:25oC, for seven generations, the proportion of diapausing adults decreased and their sensitivity to photoperiod increased. In LD 14:10 h, 40:25CC, 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.

Bruchidius atrolineatus (Pic) (Bruchidae: Coleoptera) is a bruchid beetle infesting Vigna unguiculata (Walp). During the dry season, adults are in reproductive diapause. Studies of adult populations in a traditional store containing contaminated pods of V. unguiculata show that the reproductive diapause is induced during the first larval instars. The temperature decrease from November to January probably is the main climatic factor inducing this diapause. The percentage of diapausing adults depends on the duration of the larval development at low temperatures. Experiments in climatic boxes confirm these results. At 12 h 25 °T–12 h 20° C 11–13 LD, a high proportion of the adults emerging from the V. unguiculata seeds are in reproductive diapause and the duration of their growth is variable. L1 L2 L3 larvae probably are sensitive stages to the thermal variations and the processes allowing emergence of diapausing adults probably are induced during these larval instars. Resume Induction de la diapause reproductrice chez Bruchidius atrolineatus coleoptere bruchidae durant la saison seche en zone Sahelienne Bruchidius atrolineatus (Pic) est un Coleoptere Bruchidae se developpant en zone sahelienne aux depens d'une legumineuse Vigna unguiculata. Pendant la saison seche, les adultes sont en diapause reproductrice. Un suivi des populations d'adultes a ete realise dans un grenier traditionnel en ‘terre sechee’ contenant des gousses recoltees dans la nature et portant des œufs de B. atrolineatus. Il a permis de constater que la diapause reproductrice etait induite durant les premieres phases du developpement larvaire. La decroissance des temperatures de Novembre a Janvier avec des minima de 15 °C et des maxima de 25 °C est probablement le principal facteur permettant l'induction de cette diapause. L'introduction dans le grenier de gousses portant des œufs venant d'etre emis a differentes periodes de la saison seche montre que le pourcentage d'adultes diapausants depend de la duree du developpement larvaire aux temperatures ‘basses’. Des experiences realisees dans des etuves programmees confirment ces resultats. A 12 h 25 °T/12 h 20 °C 11–13 LD, un taux eleve d'adultes emergeant des graines est en diapause reproductrice et la duree de leur developpement post-embryonnaire est tres variable. En conditions plus chaudes 12 h 40 °C/12 h 25 °C 11–13 LD, le taux d'adultes diapausants est plus reduit et la duree du developpement plus courte. L'analyse de la croissance larvaire montre que les premiers stades larvaires sont probablement des stades sensibles aux variations thermiques. Les modifications physiologiques permettant l'emergence d'adultes diapausants ou sexuellement actifs seraient induites durant ces stades.