Emergence and survival of leafcutter bees, Megachile rotundata, held at constant incubation temperatures (Hymenoptera: Megachilidae)

Survival and development of prepupae of the alfalfa leafcutter bee, Megachile rotundata (F.), for 4 locations in Alberta, Canada, were investigated during incubation of cocoons at eight constant temperatures in the laboratory. Good survival was observed for incubation temperatures of 20-32°C and there was no significant interaction in postoverwintering mortality between males and females. In some cases, prepupae held at 35 or 37°C went through a state of arrested development for 2-3 weeks, which may be a form of aestivation. Development times at seven constant temperatures by location and sex are provided. There were no significant differences among locations in mean development time and a common linear regression equation for development versus temperature was determined. Threshold temperature for prepupal development was estimated to be 15.7°C and 295 accumulated 'degree-days' were required for 50% completion of adult emergence. This information was used for successful prediction of adult emergence when leafcutter bee cocoons were placed in a commercial incubator. The duration and temperature of cold storage for cocoons prior to incubation must be standardized to allow homologous comparisons of research results.