1a. Objectives (from AD-416):
The objective of this cooperative research is to raise and manipulate M. rotundata females nesting in field cages so as to capture the bees while performing specific behaviors related to different behavioral and physiological states. Genetic analysis of bees collected in the different states will be performed to determine any differential gene expression between states. This study is part of a larger sociogenomic study for exploring the molecular evolution of sociality in Hymenoptera.
1b. Approach (from AD-416):
Megachile rotundata adults will be reared in the ARS laboratory. The adult bees will then be released into field cages where their nesting activities will be monitored and manipulated for obtaining bees of different behavioral and physiological states. Freezer-killed adults will be shipped/transported to University of Illinois where bees will be dissected and genetic analyses will be performed.
3. Progress Report:
A manuscript was completed for submission to BMC Evolutionary Biology that incorporated the work done on nesting behavior and impact on larval development as a part of this agreement. Some solitary bees produced in the same season enter a diapause state while others complete development, and this flexibility in diapause may be related evolutionarily to social bee caste determination (castes are queens, workers, and drones). We used the alfalfa leafcutting bee as a model because it has developmental plasticity in larval diapause and it is an important commercial pollinator that can be reared in large numbers. We investigated how the main regulator of social bee caste determination, larval nutrition, affects whether a solitary bee enters or bypasses diapause. Field surveys of natural larval provisions (nectar plus pollen food masses) and experimental manipulations of larval diet quantity and quality in the laboratory revealed that there is nutritional regulation of diapause plasticity in leafcutting bees. Higher diet quantity increased the probability of entering diapause, suggestive of what is known about how diet quantity influences development into the reproductive queen or sterile worker caste in many social bees. Surprisingly, when the quality of larval nutrition was altered by the addition of royal jelly (the caste-determining substance produced by honey bees), individual leafcutting bees exhibited a decrease in adult body weight, but were more likely to enter diapause. These results suggest that royal jelly can affect the internal nutritional regulation of diapause in solitary bees and support the hypothesis that pathways regulating diapause plasticity in solitary bees may also regulate caste determination in social bees. We also found that, as in social bees, larval nutrition can affect female leafcutting bee reproductive behavior. These effects were mediated through the influence of body weight and diapause status on nesting success in the context of limited or unlimited nesting sites. This study provides evidence that there is nutritional regulation of diapause in a solitary bee and suggests that some of the mechanisms involved in solitary bee diapause plasticity may have been involved in the evolution of social bee castes.