A neonicotinoid pesticide alters how nectar chemistry affects bees

Neonicotinoid pesticides in the nectar and pollen of managed crops and wildflowers contribute to the global declines of bees. These chemicals can have detrimental effects on bees' physiology, behaviour and reproduction. Floral nectar also contains secondary chemistry with its own effects on bee health. How nectar secondary chemistry may act additively or synergistically with neonicotinoids is unknown. Here, we asked how an acute exposure to a common neonicotinoid, imidacloprid (IMD) affected the longevity, immune function and behaviour of bumble bee Bombus impatiens workers maintained on diets enriched with one of three nectar secondary metabolites (NSMs; the alkaloid caffeine, the terpenoid thymol or the cardiac glycoside digoxin). A factorial design allowed us to assess the potential for additive and interactive effects of each NSM and IMD combination on multiple health outcomes. Without IMD exposure, different dietary NSMs each had positive effects on life span (caffeine), immune function (digoxin) and activity levels (caffeine, thymol), although these came with trade-offs. A single sublethal IMD exposure overshadowed these NSM effects, and in two cases, an NSM-enriched diet magnified the negative effects of pesticide exposure. In summary, we show that even a single acute exposure to a pesticide has the potential to reshape interactions between pollinators and plants mediated by nectar secondary chemistry. Read the free Plain Language Summary for this article on the Journal blog.

Automated summary

This study found that even a single acute exposure to a pesticide has the potential to reshape interactions between pollinators and plants mediated by nectar secondary chemistry.