Bruchidius atrolineatus (Pic) is present in crops of Vigna unguiculata towards the end of the dry season at the beginning of September when pods start to form. Females lay many eggs on most available green pods. However, this oviposition behaviour results in an important egg mortality. During September, pods gradually reach maturity whilst new pods are formed. Females therefore have at their disposal a growing number of differently mature pods. Confronted with such a situation, B. atrolineatus females show an opportunist behaviour and lay most of their eggs on the most abundant stage, i.e. the most easily discovered stage (ripening green pods in mid-September or dry pods towards the end of September). However, they also lay eggs on other phenological stages no matter how abundant they are. B. atrolineatus females therefore show a certain behavioural plasticity enabling them to reproduce on all stages of pods whose maturity, chemistry and texture may differ. Larvae can develop either in maturing or dry seeds. The number of eggs laid from mid September is lower and lower whatever the phenological stage attacked. This decrease would be due to a reduction of the first generation adult bruchids and of the reproductive potential of females.Callosobruchus maculatus appears in crops at the same time as B. atrolineatus, but oviposits preferentially on dry pods. Eggs are observed during the whole period of study, but the numbers laid are always low. With the increase in pod number, eggs are dispersed among the different substrates available. However, the average number of eggs laid on the pods remains constant. Despite the high mortality due to the oviposition behaviour of B. atrolineatus and to other factors (impact of hymenopterous parasitoids), these two bruchids cause important losses to seeds of V. unguiculata. Control methods against these pests should be envisaged .in the field before harvesting.

No abstract

La présence des gousses et graines de six espèces de Phaseolus déclenche une ponte importante chez A. obtectus et stimule significativement la production ovarienne. Cependant, les meilleures performances ne sont pas observées avec P. vulgaris, hôte habituel, mais avec P. coccineus. Pour toutes ces espèces le tégument de la graine représente une barrière importante pour la pénétration des larves. Chez certaines espèces sauvages, et dans les conditions expérimentales, il permet une protection totale de la graine. Cette protection semble diminuer avec la domestication chez P. vulgaris. Lorsque les graines sont perforées artificiellement, les larves (une par graine) pénètrent sans difficulté, quelle que soit l'espèce. Les graines de P. coccineus et de P. vulgaris permettent le développement complet de la majorité des larves, tandis que dans celles de P. metcalfei et de P. acutifolius ne peut se développer qu'une faible partie de la population larvaire. Certains Phaseolinae peuvent donc stimuler la ponte sans permettre le développement des larves. Les femelles de la F1 ***provenant de P. coccineus ont des performances reproductrices supérieures à celles des femelles provenant de P. vulgaris (variétés sauvage ou cultivée). P. coccineus pourrait être considéré comme une des plantes‐hôtes d'origine.