Neonicotinoids override a parasite exposure impact on hibernation success of a key bumblebee pollinator

Abstract

Abstract. 1. Seasonal adaptations enabling the bridging of periodic challenging abiotic conditions are taxonomically widespread. However, sensitivity to other environmental stresses can be heightened during these periods.2. Several temperate insects with over-wintering strategies play key ecosystem and economic roles, including wild bee pollinators. For example, hibernation survival in temperate bumblebees is crucial, as only new queens of future social colonies over-winter. These bees are also faced with other abiotic and biotic stressors, some of which have been linked to recent pollinator declines, such as exposure to pesticides and parasites.3. Using a fully crossed experiment, the influence of dietary exposure to neonicotinoid insecticides (thiamethoxam and clothianidin) and/or the prevalent bumblebee parasite Crithidia bombi on hibernation survival and hibernation weight change of Bombus terrestris bumblebee queens was investigated.4. Both neonicotinoid and C. bombi exposures reduced hibernation success individually, but no additive or synergistic effects between the stressors were found. Further, effects were asynchronous, with early neonicotinoid effects on hibernation mortality overriding later parasite effects under combined exposures. Neonicotinoid exposure also increased hibernation weight loss of surviving queens.5. Diapause periods, employed by numerous temperate organisms, are likely to be especially vulnerable to environmental stresses, besides the seasonal challenge for which these periods are an adaptation. Thus, diapause requires inclusion during the consideration of the impacts of such stresses. Accordingly, it is demonstrated here that naturally relevant exposures of pesticides and parasites have important detrimental effects on bumblebees during a critical hibernation period, with potential consequences for populations of these key wild pollinators.

Effects of neonicotinoid insecticide exposure and monofloral diet on nest-founding bumblebee queens

“…B 285: 20180761 exposure levels in some landscapes. Our study is one of a small but growing number of studies examining the unique effects of neonicotinoid exposure on the solitary life-history stages of bumblebee queens [36,39,40,69]. Collectively, these studies suggest that there are unique deleterious effects on queens that can have dramatic consequences for reproduction and nesting success.…”

Effects of neonicotinoid imidacloprid exposure on bumble bee (Hymenoptera: Apidae) queen survival and nest initiation

“…Some studies have focused on the reproductive potential of worker bees in queenless colonies, and worker fecundity in queenright colonies (Laycock et al 2012(Laycock et al , 2013Whitehorn et al 2012); however, little has been researched on the direct impacts on queen bumble bees. More recent work has shown adverse effects on hibernation success, ovary development, and fecundity in Bombus terrestris (L.) (Hymenoptera: Apidae) queens exposed to the neonicotinoid, thiamethoxam (Baron et al 2017, Fauser et al 2017. Baron et al (2017) also showed species-specific responses to thiamethoxam consumption and toxicity in four different bumble bee species (Bombus terrestris, Bombus lucorum (L.), Bombus pratorum (L.), and Bombus pascuorum (L.) (Hymenoptera: Apidae)), which highlights the need for more information about the potential impacts on other bumble bee species.…”

Temperature dependence of parasitic infection and gut bacterial communities in bumble bees

“…Each spring, solitary queen bumble bees face thermoregulatory challenges as they emerge from hibernation to establish new colonies. This is also the stage of the life cycle at which C. bombi can be most virulent (Brown et al, 2003;Fauser et al, 2017). The availability of adequate early season floral resources may be a key determinant of the ability of queens to maintain body temperatures necessary for foraging, brood incubation and parasite inhibition.…”