Plant-species identity of pollen collected by bumblebees placed in greenhouses for tomato pollination

The seasonal variation of pollen collected from different plant species by greenhouse bumblebees was investigated to determine how frequently bumblebees forage outside of commercial tomato greenhouses. Pollen was collected from bumblebees at three greenhouses between February and September 2001 and the plant species identity of pollen collected was determined with light microscopy. A significant amount of non-tomato pollen was collected by bumblebees during. one or more months from outside each of the three greenhouses studied. The bees brought black as little as an average of 5% non-tomato pollen between February and September at one greenhouse and as much as 73% during July at another. Therefore, greenhouse, tomato growers are probably not obtaining maximum pollination benefit from bumblebee colonies and should address methods to reduce their foraging outside the greenhouse.