Wild bees live in temporally and spatially heterogenous environments. Understanding this variation is necessary to predict how wild bees will respond to future landscape change, but extremely little is known about their life cycles other than foraging ecology. We studied the nesting phenology and dynamics of two spring-emerging solitary bees, the pollen-generalist Colletes inaequalis and the Ericaceae-specialist Colletes validus in Concord, New Hampshire. During spring 2018, we monitored the fates of all nests within ten nesting aggregations by conducting surveys every 1-5 days throughout the flight season. A nest was recorded as active if any visible signs of activity were observed. For both species, we explored variation in nesting phenology and dynamics within and among aggregations. To assess within-aggregation phenology, we used linear models to test whether the average duration of nesting changed throughout the season. To assess between-aggregation nesting dynamics, we tested whether the mean start date of nesting differed significantly among aggregations. We also compared rates of nesting in aggregations by fitting logit-normal curves to cumulative nesting data and comparing the slopes.
Results/Conclusions
On average, C. inaequalis nests were active for 11.7 days (n = 294), whereas C. validus nests were active for 8.0 days (n = 546). Nests of both species that were initiated late in the season were not active for as long as those initiated earlier. Concurrent field observations indicated abandonment of late-season nests by C. validus coinciding with host plant decline. Second, the mean date of nesting differed significantly among aggregations. For C. validus, nesting occurred in two distinct periods and the mean start dates of aggregations in these two periods were approximately two weeks apart. Two hypotheses could explain these results: late aggregations consist of 1) re-nesting females or 2) a distinct cohort of late-emerging bees. Last, C. inaequalis and C. validus aggregations grew at different rates, with small, late-season aggregations reaching their maximum number of nests faster than early-season aggregations. In sum, we found that solitary bee phenology and nesting dynamics vary significantly across space and time. Yet, our results raise more questions than they answer, and a logical next step would be to describe the mechanism generating this variation in solitary bee life history.