Methods for increasing squash bee longevity in the laboratory

Performing pesticide bioassays is an important step in determining the risk to pollinators from agrochemicals. These bioassays are commonly done on social bees like Apis mellifera and Bombus spp., as well as on solitary cavity-nesters like Osmia and Megachile spp. Solitary ground-nesting bees, which make up the majority of bee species, are rarely used in bioassays due to the difficulty of acquiring them in sufficient quantities. The squash bee Xenoglossa pruinosa is a solitary ground-nesting bee that can be found in large numbers in commercial pumpkin and squash fields and are easy to collect. Unfortunately, they exhibit high mortality when kept in the laboratory and tend to not live long enough to perform a chronic bioassay. 

We attempted to develop methods to improve the longevity of X. pruinosa in the laboratory. Squash bees were collected from pumpkin flowers, refrigerated overnight, then distributed to cages. We experimented with several types of feeders and cage designs to minimize mortality. We also tested cinnamaldehyde as a feeding stimulant, with non-significant but promising results. Lastly, we performed an acute topical bioassay with a combination of the insecticide active ingredient acetamiprid and the fungicide active ingredient triflumizole, and compared the results with a similar bioassay with A. mellifera. Control mortality was unfortunately still higher than is desirable in a bioassay. While we were able to increase longevity, more work needs to be done to determine optimal methods before X. pruinosa can be used as reliably in pesticide bioassays as can A. mellifera.