Bumble bee (Hymenoptera : Apidae) activity and pollination levels in commercial tomato greenhouses

Commercial greenhouse studies were conducted to assess levels of pollinatio n of tomato (Lycopersicon esculentum Mill.) flowers in relation to bumble b ee (Bombus impatiens Cresson) colony activity and colony densities. For the assessment of pollination levels of tomato flowers, five categories were d efined based on bruising levels caused by bumble Lee pollination. Colony ac tivity was measured as bee trips per ha/d using electric powered photodiode monitors inserted into the hive entrance. Levels of pollination were posit ively correlated with bee activity levels, up to a mean of approximate to 4 00 pollen grains per stigma per day, after. which greater activity did not result in further increases in daily pollination levels. Densities of colon ies in the commercial greenhouses studied ranged from 7.6 to 19.8 colonies per hectare with a mean of 11.6 +/- 0.9. We found that an average activity of 2,000 bee trips per hectare per day was more than adequate to ensure suf ficient pollination, and that this level of activity could be achieved with 7-15 colonies per hectare, depending on greenhouse conditions. Greenhouses requiring >15 colonies per hectare to achieve this level of pollination ma y be able to increase bee activity, through alteration of greenhouse condit ions. Across 50-m rows of tomato plants, levels of pollination decreased wi th increasing distance from bee colonies, suggesting that colonies should b e evenly distributed throughout the greenhouses.