Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 19, 2000
Publication Date: March 1, 2001
Citation: Kemp, W.P., Bosch Gras, J. 2001. Post-cocooning temperatures and diapause in the alfalfa pollinator megachile rotundata (hymenoptera: megachilidae). Annals of the Entomological Society of America. Interpretive Summary: Alfalfa seed producers frequently complain about losses that they suffer in populations of the alfalfa leafcutting bee, the most commonly used bee pollinator of alfalfa grown for seed in the western United States. One such "loss" is "second generation", the premature emergence of current year brood which reduces the population of alfalfa leafcutting bees for next year's pollination season. Alfalfa seed producers would like to see research conducted on the biological reasons for differences that they see in the frequency of "second generation" losses from year to year. The results that we obtained from a series of controlled experiments show that high late summer temperatures will increase the frequency of "second generation", and we provide some simple suggestions that alfalfa seed producers can adopt to reduce such losses.
Technical Abstract: Megachile rotundata (Fabricius), an adventive, gregarious, cavity-nesting, leafcutting bee, is used throughout North America for the pollination of alfalfa, Medicago sativa L., seed crops. We examined the influence of various post-cocooning (pre-wintering) temperature regimes on development, survival, emergence time, and longevity in both non-diapausing and diapausing forms of this species. Diapausing male and female M. rotundata required 27-30 d and 29-32 days, respectively, to develop from prepupae to emergence following incubation at constant 29C, regardless of post- cocooning treatments to which they were exposed. Likewise, longevity following emergence were not related to post-cocooning temperatures and ranged from 5-6 d and 4-6 d for males and females, respectively. Elevated post-cocooning temperatures were associated with a higher prevalence of non-diapausing individuals, those completing development from eggs through emergence as adults in the same summer season. Relevance of our results t the commercial production of alfalfa leafcutting bees is discussed.