A field study comparing development of Bombus impatiens (Hymenoptera: Apidae) colonies exposed to conventional neonicotinoid seed treated and organic corn fields during pollen shed in Southern Ontario

Abstract

A field study was conducted to determine the effects of neonicotinoid seed treated corn on Bombus impatiens colony health, when commercial hives were present during pollen shed. Fields contained corn that had been seed treated with clothianidin, thiamethoxam, both, or neither. Collected pollen was analysed for species content and corn pollen was analysed to determine pesticide loads. Multiple endpoints were measured to determine colony health, including worker numbers and weights, drone numbers and weights and queen numbers and weights. Number of brood cells, honey pots and pollen pots were also compared. Pollen analysis showed that bumble bees foraged very little on corn, and that the amount of clothianidin expressed in the corn pollen was well below limits used in most laboratory studies where no adverse effects are seen. In addition to this, hives placed in seed treated fields were found to be of comparable colony health to hives placed in untreated fields, although worker numbers were found to be higher in hives that had been placed in untreated fields. This difference is most likely due to a batch effect, based on the minimal of corn pollen collected combined with the low expression of clothianidin in the pollen.