regulation of size related division of labor in a key pollinator and its impact on crop pollination efficacy

Despite the rapid increase in reliance on bumble bees for food production and security, there are many critical knowledge gaps in our understanding of bumble bee biology that limit their colony production, commercial management, and pollination services. Our project focuses on the social, endocrine, and molecular processes regulating body size in the two bumble bee species most important to agriculture: Bombus terrestris in Israel, and B. impatiens in the USA. Variation in body size underline both caste (queen/worker) differentiation and division of labor among workers (foragers are typically larger than nest bees), two hallmarks of insect sociality which are also crucial for the commercial rearing and crop pollination services of bumble bees. Our project has generated several fundamental new insights into the biology of bumble bees, which can be integrated into science-based management strategies for commercial pollination. Using transcriptomic and behavioral approaches we show that in spite of high flexibility, task performance (brood care or foraging) in bumble bee colonies is associated with physiological variation and differential brain gene expression and RNA editing patterns. We further showed that interactions between the brood, the queen, and the workers determine the developmental program of the larva. We identified two important periods. The first is a critical period during the first few days after hatching. Larvae fed by queens during this period develop over less days, are not likely to develop into gynes, and commonly reach a smaller ultimate body size compared to workers reared mostly or solely by workers. The facial exocrine (mandibular and hypopharangeal) glands are involved in this queen effect on larva development. The second period is important for determining the ultimate body size which is positively regulated by the number of tending workers. The presence of the queen during this stage has little, if at all, influence. We further show that stressors such as agrochemicals that interfere with foraging or brood care specific processes can compromise bumble bee colony development and their pollination performance. We also developed new technology (an RFID system) for automated collection of foraging trip data, for future deployment in agroecosystems. In spite of many similarities, our findings suggest important differences between the Eurasian model species (B. terrestris) and the North American model species (B. impatiens) that impact how management strategies translate across the two species. For example, there is a similar influence of the queen on offspring body size in both species, but this effect does not appear to be mediated by development time in B. impatiens as it is in B. terrestris. Taken together, our collaboration highlights the power of comparative work, to show that considerable differences that exist between these two key pollinator species, and in the organization of young bumble bee nests (wherein queens provide the majority of care and then transition away from brood care) relative to later stages of nest development.