PS 48-243 - Does aerial mosquito control spraying have any effects on wild bees in Plymouth County, Massachusetts?

Abstract: The risk to pollinators from aerial mosquito control spraying has been a concern for some time. Spraying via airplane or helicopter is done when a large area is at high risk for human disease. To minimize risk to the bee community, low concentrations of the insecticide AnvilⓇ 10+10 ULV are used and treatment is done overnight when bees are less active. However, there is little research assessing the effectiveness of these preventative measures. Furthermore, studies have focused primarily on Apis mellifera in risk assessments while overlooking other important pollinators. We investigated the possibility of acute effects of aerial mosquito control spraying on wild bees in Plymouth County, Massachusetts. Pollinator collection was conducted during a long-term monitoring study from 2016-2021 at six sampling sites ranging from peri-urban to urban landscape. The length of this study presented the opportunity to use data during years aerial spraying occurred (n=2) and years where it did not (n=4). Abundances of bees, excluding domesticated Apis, were compared before (early August) and after spray events (late August) to evaluate potential changes to the bee community. Abundances were also compared over the same portion of the season in non-sprayed years.

Unexpectedly, increased bee abundance was observed post-insecticide application compared to the same time point in non-spray years. Average total bee abundance increased by 54% from 43 to 65 bees per sample before and after the spray event. At the same sites, bee abundance in non-spray years over the same portion of the season averaged 38 and 40 bees per sample before and after, respectively, remaining stable. These observations could be due to natural random variation or attributed to other factors affecting pollinator presence. Although there was an upward trend in abundance, it was not statistically significant. However, our results provide no evidence of an acute negative effect of aerial spraying. Additional spray events and sampling events should be investigated to further assess the possible effects of mosquito control spraying on the bee community.