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
Studies on the effect of temperature on leafcutting bees were continued and expanded. Different summer rearing temperatures were evaluated to determine the effect on overwintering survival of the bees, the fat content of the bees (as a measure of bee health), and second generation production (i.e., the probability that bees will not go into winter dormancy, generally considered a negative result). Forty nests kept at 32C (90F) produced 2.6 second generation adults per nest, whereas nests kept at 22C (72F) and 28C (82F) produced an average of just 0.1 and 1.2 bees per nest, respectively. We conducted a parallel study where bees were removed from nesting shelters at different times during the summer and placed directly on a thermal gradient. This study needs to be repeated, and full data analysis conducted, before conclusions can be made. A study examining how temperatures in the fall affect this bee’s ability to survive over winter was completed with a third year of data. In the data analyzed thus far, bee survival was unaffected by fall temperatures. Another study was initiated to examine how variable temperatures and variable duration of fall storage conditions, combined, affect survival of the bees over winter. This first year’s attempt was affected by unusually high second generation emergence. Lastly, we completed analysis of data from our 3-year study of post-winter development, examining the data with a set of biologically-realistic statistical models not previously applied to leafcutting bees. These models, along with the wide range of temperature treatments we used, allowed us to estimate not only the minimum temperature for development (as in previous studies), but the optimum temperature (where the rate is fastest) and maximum temperature (above which development ceases and bees die relatively quickly). Our calculations for minimum and optimum temperatures are similar to previous studies, but our results predict lower values for maximum rearing temperatures and are more in agreement with our previous observations that long-term temperature-related mortality increases rapidly above 35C. One difficulty that could arise in light of our results is that it may be difficult to maximize the rate of development [which is highest at 33-34C (91-93F)], while simultaneously maximizing emergence success [which declines above 32C (90F)] and fat content [which is highest at about 27C (81F)]. By carefully timing when bees are removed from winter storage, and avoiding high temperatures, growers should be able to produce healthy bees without high temperature-related mortality. ADODR monitoring is done through phone calls, emails, and discussions at professional meetings.