L'activité de butinage des Apoides sauvages (Hymenoptera Apoidea) sur les fleurs de maïs à Yaounde (Cameroon) et réflexions sur la pollinisation des graminées tropicales

The gatering activity of wild bees (Hymenoptera Apoidea) on flowers of maize at Yaound (Cameroon) and further considerations on pollination of the tropical Gramineae. At Nkolbisson (Yaounde, Cameroon), in May 1991, flowers of maize (Zea mays L; Poaceae) were observed for the study of pollen gathering by five different species of wild bees: one Apidae Meliponinae (Dactylurina staudingeri) and four Halictidae Nomiinae (Lipotriches andrei, Lipotriches langi, Lipotriches notabilis and Leuconomia granulata). Each of these Apoidea is well attracted by pollen of maize. The larger number of bees foraging at the same time on a panicle varies from one with Dactylurina staudingeri to four with Lipotriches andrei and Lipotriches notabilis. Generally, bees forage maize during the whole day and during the full flowering period but visits are more numerous in the morning and during the period of intense flowering. Median duration of a visit on a male spikelet varies from 1 sec with Dactylurina staudingeri to 7 sec with Lipotriches andrei. These Apoidea have an elaborated behaviour when gathering pollen of maize. Dactylurina staudingeri however seems less adapted to the floral morphology of Poaceae comparing with Lipotriches. When foraging maize, all these bees are regular visitors to flowers of this plant, even in the presence of other flower species in the vicinity of the crop. Bees studied have a positive impact on the yield of grains due to a complementary action with the well known one of the wind. The influence is indirect as the bees are seldom visiting the stigmates. The explanation is that when the bees are very common on the panicles they shake the anthers, inducing the release of pollen grains in the atmosphere even in the days without wind. The part of wild bees in the increase of yields is estimated to 3/ while the one of the domestic bees (Apis mellifera) is estimated to 21/ in that locality. The authors are reviewing existing literature on grass crop pollination and on Poaceae in general by various species of bees. For a better integrated crop management of maize in Cameroon, it is suggested to conserve the nesting sites of Lipotriches in surrounding areas of crops and to avoid unjustified use of pesticides during the flowering period.