Background/Question/Methods Many taxa produce offspring with variable dormancy times. Such life histories could be beneficial when future environmental conditions are unpredictable; in those cases, producing some offspring that remain dormant for many years, instead of just one, could increase long-term fitness. However, the environmental cues affecting the decision to enter dormancy are rarely known. Here, I present results from an experiment testing how two environmental factors—temperature and nutrition—shape dormancy in a parsivoltine solitary bee, Colletes validus. Some offspring develop in one year (one-year bee), whereas the remaining enter dormancy and develop over two years (two-year bee). I predicted that the probability of entering dormancy would increase at low temperatures by reducing developmental rate and under supplemental nutrition by delaying metamorphosis. In summer 2020, I collected C. validus brood cells (n = 181) containing early-instar larvae from wild nests in Massachusetts, USA. Brood cells were randomly assigned to one of four rearing treatments in a crossed design: temperature (low 18C vs. high 24C) and nutrition (no supplement vs. +20% pollen supplement by mass). Developmental stage was monitored weekly until each offspring had either eclosed as an adult (one-year bee), arrested development as a post-feeding larva (two-year bee), or died. Results/Conclusions C. validus bee voltinism was sensitive to temperature, but not nutrition. In cool conditions (18C), 26-28% of larvae committed to a two-year life cycle regardless of nutrition. In contrast, less than 3% of larvae reared in warm conditions (24C) committed to a two-year life cycle. There were no differences in survival rate among treatments (mean = 0.53), and these results will be complemented with data on the sex ratio and fates of two-year bees during their second year. While cool temperatures were sufficient to induce dormancy, some offspring still committed to a two-year life cycle in the warm treatment, suggesting that other cues are also important determinants of life cycle length. These results are consistent with dormancy rates in wild C. validus populations—5-17%—where summer air temperatures (19-21C) fall in the middle of temperatures tested in the lab. To the extent that we can extend lab results to performance in the wild, my results indicate that C. validus voltinism will be more sensitive to climate change than land use change. Understanding the environmental drivers of bee voltinism is important for predicting the fate of pollinator populations in human-altered landscapes.
