A neonicotinoid pesticide alters how nectar chemistry affects bees

Abstract

1. Neonicotinoid pesticides in the nectar and pollen of managed crops and wild-flowers contribute to the global declines of bees. These chemicals can have det-rimental effects on bees' physiology, behaviour and reproduction. Floral nectar also contains secondary chemistry with its own effects on bee health. How nec-tar secondary chemistry may act additively or synergistically with neonicoti-noids is unknown.2. Here, we asked how an acute exposure to a common neonicotinoid, imidaclo-prid (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 thy-mol 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.3. 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 over-shadowed these NSM effects, and in two cases, an NSM-enriched diet magni-fied the negative effects of pesticide exposure.4. 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.