Honey bee (Apis mellifera L.) and bumble bee (Bombus impatiens cresson) pollination efficacy on field-grown cucumber and watermelon

Parasites and other problems plague the American beekeeping industry, resulting in a nationwide reduction in the number of honey be (Apis mellifera L.) colonies available for crop pollination. Bumble bee (Bombus spp.) colonies are now commercially-available in the United States and may provide an alternative pollination source for many insect-pollinated crops. Previous work by the author demonstrated the value of Bombus pollination on field-grown cucumber and watermelon at the individual bee-level (i.e., the number of bee visits to pistillate flowers required to set fruit comparable to flowers that received unlimited, or open, insect pollination).; Additional field studies were conducted to evaluate bumble bee versus honey bee pollination of field-grown cucumber and watermelon on other level which contribute to a species' overall potential utility as a commercial pollinator. The studies compared honey bee and bumble bee: (1) foraging activity periods (the onset, peak, and termination of foraging activity in relation to floral anthesis and duration); (2) floral visitation rates (the number of flowers visited per unit time by individual foragers; and (3) stigmatic pollen deposition (the number of pollen grains deposited on stigmas after single bee visits to pistillate flowers).; Bumble bees outperformed honey bees in all three comparative experiments on both cucumber and watermelon. Bumble bees initiated foraging activity 30 min before honey bees. This additional foraging time for Bombus may prove advantageous when high temperatures reduce floral receptivity to just a few morning hours.; Bumble bees also consistently visited more flowers per min and deposited equal or greater amounts of pollen than honey bees on both crops ( P < 0.0001 for all tests). On cucumber, bumble bees visited an average of 2.12 times as many flowers per min and deposited 1.34 times as many pollen grains per visit than honey bees. On watermelon, bumble bees visited on average 2.35 times as many flowers per min and deposited 2.74 times as many pollen grains per visit than honey bees. Differences in floral visitation and pollen deposition rates between bee species were even greater during earlier morning sampling periods, which is when most cucurbits are optimally receptive under typical field conditions.