Comparing the foraging behaviour and pollination efficiency of Apis mellifera with Xylocopa olivacea (Apidae: Hymenoptera) on Citrullus lanatus flowers

Abstract

Comparing the foraging behaviour and the pollination efficiency of honey bee (Apis mellifera) with a carpenter bee (Xylocopa olivacea) in the farmer garden of watermelon (Citrullus lanatus) was conducted in Maroua (Cameroun) in 2016 and 2017. Several foraging parameters were assessed for each bee species during the blooming period of watermelon and comparisons were made between fruit and seed yields from four pollination treatments on female flowers including the no bee visit treatment (T0), the one bee visit treatment for A. mellifera (T1) and X. olivacea (T2) and the unrestricted treatment (T3). Results showed an important difference in the rhythm of activity between the two bee species with a peak of floral activity of X. olivacea at 07:00-08:00 a.m. time interval and that of A. mellifera at 09:00-10:00 a.m. A. mellifera was prominent than X. olivacea regarding the frequency of floral visits in 2016 (77.74 and 22.26 %) and in 2017 (81.28 and 18.72 %) and the density of individuals per 1000 flowers in 2016 (442/1000 flowers and 97/1000 flowers) and in 2017 (476/1000 flowers and 88/1000 flowers). Despite the higher foraging intensity of A. mellifera compared with that of X. olivacea, the carpenter bee was a more efficient pollinator than the honey bee. Indeed, the mean treatments for fruiting rate, mean fruit weight, mean fruit diameter, and mean mature seeds per fruit of watermelon were higher on the one visit basis in T2 than T1. Moreover, the unrestricted treatment T3 produced fruit with the best marketable value than restricted treatments T2, T1, and T0. X. olivacea should be associated with A. mellifera in a watermelon field to optimize the pollination of this crop for obtaining improved yields. Considering very high pollinating efficiency of X. olivacea, the means of conservation must be developed for this solitary bee which appeared in this work as a synergistic or alternative pollinator of the honey bee within a watermelon farm.