Tillage effects on the ground nesting bee Peponapis pruinosa

Roughly 70% of bee species nest in the ground. Within agricultural landscapes crop fields provide nesting habitat for some ground-nesting bees. However, crop fields experience regular disturbance in the form of tillage. Tillage is thought to negatively impact ground-nesting bees, but detailed observational studies in agricultural fields provided conflicting results. We tested the effect of tillage on offspring survival using the squash bee,  Peponapis pruinosa. We established P. pruinosa nesting aggregations in twenty 10 foot by 10 foot cages and then randomly assigned the tillage treatment to half of those cages. The following summer we trapped emerging offspring and used an over-dispersed Bayesian Poisson model to analyze the data. We found that tillage had a negative effect on offspring survival. However, the results were highly variable and some individuals survived the tillage treatment.