1a. Objectives (from AD-416)
The alfalfa leafcutting bee is a critical pollinator for alfalfa seed production. Improved methods for managing alfalfa leafcutting bee health is needed so that growers can more effectively produce their own bees and not have to rely so extensively on importing bees from Canada. The objective of this project is to construct a model that combines information regarding rearing temperatures and post-overwinter development time, survival, and adult bee condition and provide recommendations on rearing temperatures that minimize development time and variability in development rates, while simultaneously maximizing bee survival and adult bee condition.
1b. Approach (from AD-416)
The approach is relatively straightforward, involving 1) collection of bees cells at different times of year from multiple sources, 2) dissection of large samples of bees cells to diagnose mortality factors, and 3) conducting life-table analyses. The latter is being done at Montana State University which has expertise on life table analyses, including accounting for irreplaceable mortality. The analyses will be done using a computer program developed specifically for these analyses. Overall, the study should provide new insights into benefits to be obtained from potential strategies for reducing developmental mortality of alfalfa leafcutting bees.
3. Progress Report
The effect of post-wintering rearing temperatures on the survival of alfalfa leafcutting bees was evaluated in precisely controlled conditions over a wide range of temperatures. Alfalfa leafcutting bees were evaluated in the laboratory on a thermal gradient, and the body size, fat content of adult bees, and survival rates were measured. This three year study of post-wintering rearing temperatures has led to the following conclusions: 1) the fastest development occurs from 29-33oC (84-91 degrees F), 2) temperatures in excess of 33 degrees C actually prolonged development of some bees, resulting in late emergence that could also place many females out of sequence with peak bloom, 3) the synchrony of emergence among bees was also highest from 29-33 degrees C, 4) at the lowest temperatures (20-21oC; 68-70 degrees F), development stalled in the pre-pupal stage, but even at temperatures up to 23 degrees C (73 degrees C), many adult bees remained in cells without emerging for long as 3 months after rearing began, 5) results varied somewhat between the 3 years, but the highest proportion of successfully-emerged adult bees came from cells reared at 26-32 degrees C (79-90 degrees C), 6) body size of emerging adults, measured as head width, did not vary with rearing temperature, and 7) rearing temperature had a significant influence on the proportion of a bee’s body weight that consisted of fat. The overall conclusion at this time is a reaffirmation of the notion that bees reared at 29-30 degrees C have the most rapid and synchronous development. The results also provide evidence that such bees become adults with higher fat stores and perhaps better overall health. Parallel studies were also conducted to determine how the emergence success and health of adult bees is affected by 1) variable pre-wintering temperatures during the period just subsequent to removal of bees from the field; 2) the effect of varying both temperature and the duration of the pre-wintering period; and 3) the effect of varying wintering temperatures. ADODR monitoring is done via e-mail and phone calls, discussions at professional meetings.