Bombus huntii, Bombus impatiens, and Bombus vosnesenskii (Hymenoptera: Apidae) Pollinate Greenhouse-Grown Tomatoes in Western North America.

Abstract

Bumble bees (Bombus) are the primary pollinators of tomatoes grown in greenhouses and can significantly increase fruit weight compared with tomatoes that receive no supplemental pollination. More than a million colonies are sold worldwide annually to meet pollination needs. Due to mounting concerns over the transportation of bumble bees outside of their native ranges, several species native to western North American are currently being investigated as potential commercial pollinators. Here, two western, Bombus huntii Greene and Bombus vosnesenskii Radoszkowski, and one eastern species, Bombus impatiens Cresson, are compared for their efficacy as pollinators of greenhouse-grown tomatoes. In two experiments, colonies were placed in greenhouses and compared with control plants that received no supplemental pollination. In the first experiment, seed set was significantly increased with B. huntii pollination in one variety of cherry tomatoes. In the second experiment comparing all three bumble bee species, fruit weight was an average of 25.2 g heavier per fruit pollinated by bees versus the control, and the number of days to harvest was 2.9 d shorter for bee-pollinated fruit. In some rounds of pollination, differences were found among bumble bee species, but these were inconsistent across replicates and not statistically significant overall. Additionally, fruit weight was shown to be highly correlated to fruit diameter and seed set in all tests and, thus, is shown to be a reliable metric for assessing pollination in future studies. These results suggest that commercialization of western bumble bees is a viable alternative to the current practices of moving of nonnative bees into western North America to pollinate tomatoes.