The Effect of Soil Disturbance and Cropping Pattern on a Specialist, Ground Nesting Bee.

Farmers depend on managed colonies of the European honey bee (Apis mellifera) for pollination, but bees native to North America also pollinate crops. Many of these native species, including the squash bee (Peponapis pruinosa), nest and overwinter in the ground. If nesting in a crop field, ground-nesting bees must contend with regular disturbance in the form of tilling and crop rotations. To test the impact of tilling on P. pruinosa offspring survival we established nesting aggregations in twenty 10 foot by 10 foot cages and then randomly assigned the tilling treatment to half of those cages. The following season we collected emerging offspring. Using an over-dispersed Bayesian Poisson model we found that tilling had a negative effect on offspring survival, but that some individuals survived the treatment. We then built a spatially explicit simulation model to determine whether tilling combined with squash (Cucurbita spp.) field cropping patterns impact regional P. pruinosa populations. Preliminary analysis of the model suggests that optimal conditions for regional P. pruinosa population growth include ensuring that squash is grown near where it was grown the previous year and avoiding deep tilling.