Pesticide use negatively affects bumble bees across European landscapes

Sustainable agriculture requires balancing crop yields with the effects of pesticides on non-target organisms, such as bees and other crop pollinators. Field studies demonstrated that agricultural use of neonicotinoid insecticides can negatively affect wild bee species1,2, leading to restrictions on these compounds3. However, besides neonicotinoids, field-based evidence of the effects of landscape pesticide exposure on wild bees is lacking. Bees encounter many pesticides in agricultural landscapes4-9 and the effects of this landscape exposure on colony growth and development of any bee species remains unknown. Here we show that the many pesticides found in bumble bee-collected pollen are associated with reduced colony performance during crop bloom, especially in simplified landscapes with intensive agricultural practices. Our results from 316 Bombus terrestris colonies at 106 agricultural sites across eight European countries confirm that the regulatory system fails to sufficiently prevent pesticide-related impacts on non-target organisms, even for a eusocial pollinator species in which colony size may buffer against such impacts10,11. These findings support the need for postapproval monitoring of both pesticide exposure and effects to confirm that the regulatory process is sufficiently protective in limiting the collateral environmental damage of agricultural pesticide use.

How competition between overlapping generations can influence optimal egg-laying strategies in annual social insects

Annual social insects are an integral functional group of organisms, particularly in temperate environments. An emblematic part of their annual cycle is the social phase, during which the colony-founding queen rears workers that later assist her in rearing sexual progeny (gynes and drones). In many annual social insects, such as species of bees, wasps, and other groups, developing larvae are provisioned gradually as they develop (progressive provisioning) leading to multiple larval generations being reared simultaneously. We present a model for how the queen in such cases should optimize her egg-laying rate throughout the social phase depending on number-size trade-offs, colony age-structure, and energy balance. Complementing previous theory on optimal allocation between workers vs. sexuals in annual social insects and on temporal egg-laying patterns in solitary insects, we elucidate how resource competition among overlapping larval generations can influence optimal egg-laying strategies. With model parameters informed by knowledge of a common bumblebee species, the optimal egg-laying schedule consists of two temporally separated early broods followed by a more continuous rearing phase, matching empirical observations. However, eggs should initially be laid continuously at a gradually increasing rate when resources are scarce or mortality risks high and in cases where larvae are fully supplied with resources at the egg-laying stage (mass-provisioning). These factors, alongside sexual:worker body size ratios, further determine the overall trend in egg-laying rates over the colony cycle. Our analysis provides an inroad to study and mechanistically understand variation in colony development strategies within and across species of annual social insects.

Can Costs of Pesticide Exposure for Bumblebees Be Balanced by Benefits from a Mass-Flowering Crop?

Mass-flowering crops provide forage for bees but also contain pesticides. Such pesticide exposure can harm bees, but our understanding of how this cost is balanced by forage benefits is limited. To provide insights into benefits and costs, we placed bumblebee colonies in 18 landscapes with conventional red clover fields treated with the neonicotinoid thiacloprid (flowers + pesticide), untreated organic red clover fields (flowers), or landscapes lacking clover fields (controls). Colonies grew heavier near thiacloprid-treated clover compared to controls lacking clover, while colonies near untreated clover did not differ from colonies in neither of the other landscape types. Thiacloprid treatment effectively controlled pests and increased bumblebee crop visitation. However, colony production of queens and males did not differ among landscape types. In conclusion, thiacloprid application in clover appears to be of low risk for bumblebees. More generally, neonicotinoids may not be equally harmful when used in flowering crops and effective low-risk pest control in such crops could potentially benefit bumblebees and crop pollination.