Biological control of bruchids infesting cowpea by the introduction of Dinarmus basalis (Rondani) (Hymenoptera: Pteromalidae) adults into farmers' stores in West Africa

Biological control of bruchids infesting cowpea stores was achieved by introducing adults of an endemic parasitoid Dinarmus basalis (Rondani) (Hymenoptera: Pteromalidae) into farmers' storage systems in the guinean zone in Togo and the sudano-sahelian zone in Burkina Faso. In the guinean zone, introduction of 20 or 40 pairs of D. basalis adults at the beginning of storage and again 15 days later reduced the development of the bruchid populations after 5 months of storage. Consequently, weight losses from 25 kg batches of treated cowpea seeds were lower than 10% as compared with around 30% in controls. In the sudano-sahelian zone, an introduction of 40 pairs of D. basalis adults at the beginning of storage and again 15 days later was effective, also maintaining seed weight losses from 25 kg batches at less than 10%. These results illustrate that biological control of bruchids by the introduction of D. basalis adults into farmers' cowpea storage systems is possible in the two climatic zones of Western Africa, and produces better cowpea seed quality. However, the introduction must take place right at the beginning of storage, and the number to be introduced must take into account the initial rate of seed infestation by the bruchids.