Effect of Temperature on <I>Osmia lignaria</I> (Hymenoptera: Megachilidae) Prepupa–Adult Development, Survival, and Emergence

Abstract

The solitary bee Osmia lignaria Say continues to be developed as an orchard pollinator in the United States and southern Canada. Female bees are active during the early spring and construct nests consisting of a linear series of unlined cells delimited by mud partitions. Cells are provisioned with a pollen/nectar mass on which an egg is deposited, and nests are sealed with a mud plug. In 1997, we initiated two experiments on the development, mortality, and emergence of O. lignaria at selected laboratory temperature regimes and outdoors. In the first experiment (published previously), we compared temperature treatments for their adequacy in maintaining healthy O. lignaria populations. In a second experiment (reported here), we determined the relationship between rearing temperatures and prepupa-adult development rates as well as emergence time and longevity after wintering and incubation the following spring. We observed important differences in O. lignaria prepupa versus pupa responses to selected temperature treatments. The relationship between temperature and days to pupa was U-shaped, with additional time to transit the prepupa-pupa interval at temperatures above and below 26 degrees C. The negative relationship between temperature and the length of the pupa to adult interval contrasts with the U-shaped thermal response observed for prepupae. Thus, with each increase in thermal heat units over the range of temperature treatments tested, we observed an additional reduction in the pupa-adult interval. Individuals reared at constant 18 degrees C required 2.4 times as many days to transit the pupa-adult interval compared with those at constant 32 degrees C. Our results suggest that there is a need for the development of regionally adapted, latitude-specific breeding populations of this outstanding orchard crop pollinator.