Pollination and yield attributes of (cowpea) Vigna unguiculata L. Walp. (Fabaceae)as influenced by the foraging activity of Xylocopa olivacea Fabricius (Hymenoptera: Apidae) and inoculation with Rhizobium in Ngaoundere, Cameroon

To determine Xylocopa olivacea impact and Rhizobium on Vigna unguiculata , field trials were carried out in 2011 and 2012 during the same cropping season. Hence, 480 flowers were labeled each year and divided into five treatments, differentiated according to whether plots were inoculated with Rhizobium or not, or plants were protected from insects activities or not and the last treatment with flowers isolated then opened only to X. olivacea. The effects of inoculums on nodulation, plant biomass and seed yield, as well as the foraging behavior of X. olivacea on flowers, the number of seeds per pod and the normal seeds rate were evaluated. Results indicate that inoculation significantly increased the number of flowers (p<0.0001), root nodules (p<0.001), plant biomass (p<0.0001), pod and seeds yields in inoculated plots. X. olivacea foraged on V. unguiculata flowers from 06.00 am to 11.00 am and throughout the whole blooming period. X. olivacea intensely harvested nectar and pollen. By comparing the yields of unprotected flowers to those of flowers isolated then open to X. olivacea, 67.89 % increase fructification index, and 13.58 % increase in the number of seeds per pod due to this bee were recorded. The synergistic activity of insects and Rhizobium increased the number of seeds per pod by 62.28 % and the percentage of normal seeds by 87.15%. Our results reveal that inoculation of cowpea plant at sowing with Rhizobium and installation of X. olivacea nest close to the field could be recommended for a sustainable pods and seed yield improvement of this crop.