In order to study the diurnal visitation of flowers of cowpea by insect pollinators, the number of open flowers of cowpea and the kind and number of insects visiting the flowers were recorded, for a period of five minutes, and at intervals of one hour, from sunrise to sunset, in a quadrat of one square metre, placed randomly, on a cowpea farm. Flowers of cowpea opened from 6:00 hr. to 13:00 hr., daily. A total of 388 open flowers and 256 insect visitors were recorded during the seven-day period of the study. 52.3% of the visitors belonged to the order Hymenoptera (honeybees, wasps and ants), 26.2% to Lepidoptera (butterflies and moths) and 21.5% to Diptera (flies). Among the hymenopterans, 42.3% were honeybees, 40.9% ants and 16.8% wasps. The results of this study suggest that, in every hour, approximately 47,000 insect pollinators (including 9,800 honeybees) were exposed to insecticide, in every hectare of flowering cowpea, if spraying was done between 6:00 hr. and 13:00 hr. Thus, to minimise the impact of insecticides on these beneficial insects, cowpea fields should be sprayed from 14: 00 hr. and beyond.
Key words: Cowpea, honeybee, insecticide, pollination, Hymenoptera
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