Nutritional stress exacerbates impact of a novel insecticide on solitary bees' behaviour, reproduction and survival

Abstract

Pesticide exposure and food stress are major threats to bees, but their potential synergistic impacts under field-realistic conditions remain poorly understood and are not considered in current pesticide risk assessments. We conducted a semi-field experiment to examine the single and interactive effects of the novel insecticide flupyradifurone (FPF) and nutritional stress on fitness proxies in the solitary bee Osmia bicornis . Individually marked bees were released into flight cages with monocultures of buckwheat, wild mustard or purple tansy, which were assigned to an insecticide treatment (FPF or control) in a crossed design. Nutritional stress, which was high in bees foraging on buckwheat, intermediate on wild mustard and low on purple tansy, modulated the impact of insecticide exposure. Within the first day after application of FPF, mortality of bees feeding on buckwheat was 29 times higher compared with control treatments, while mortality of FPF exposed and control bees was similar in the other two plant species. Moreover, we found negative synergistic impacts of FPF and nutritional stress on offspring production, flight activity, flight duration and flower visitation frequency. These results reveal that environmental policies and risk assessment schemes that ignore interactions among anthropogenic stressors will fail to adequately protect bees and the pollination services they provide.

A novel insecticide impairs bumblebee memory and sucrose responsiveness across high and low nutrition

“…In the short term, regulators should restrict flupyradifurone use to non-flowering crops, while a re-assessment of its potential risk to pollinators can be re-evaluated. Ultimately, our results, and those that came before [14,55,[89][90][91][92], have demonstrated that pesticide risk assessments globally are failing to protect bees from the unintended consequences of pesticide use. Consequently, banning or restricting the use of certain agrochemicals (e.g.…”

“…Wild bee declines are driven by a multitude of different anthropogenic stressors, including pesticide use, and loss of habitat, as a consequence of intensive agriculture [7,[10][11][12]. Pesticide use can have both lethal [13,14] and sub-lethal [15][16][17][18][19] impacts on bees at field-realistic levels, which can influence bee populations [10,11]. Loss of habitat reduces floral resources which can impair bee nutrition [20].…”

“…The interactions between these stressors can be: (i) additive, where the two stressors are equal to their combined individual effect; (ii) synergistic, where the two stressors exacerbate one another and have a greater than additive effect; or (iii) antagonistic, where the impact is lower than the predicted additive effect [23]. Previous studies have found that most interactions between pesticides and poor nutrition are additive [23][24][25][26] or synergistic [13,14,[27][28][29][30]. The underlying mechanism that determines the type of interaction (synergistic, additive or antagonistic) between pesticides and poor nutrition is poorly understood and requires further investigation [23].…”

Land-use-associated stressors interact to reduce bumblebee health at the individual and colony level

“…Because of our experimental design, we did not include colony parameters such as colony size, survival or production of reproductives; however, data concerning these traits are available in the literature for various bee species (e.g. [43][44][45][46][47][48][49], or reviewed in [89]).…”

“…Although other stressors such as nutritional stress are usually excluded, bees are challenged by a plethora of stressors in the field and, thus, investigations on a single stressor may not represent real-world field situations. Indeed, recent studies using laboratory and semi-field set-ups have demonstrated that the combined effects of nutritional stress and insecticides exacerbate each other, while high-quality diet buffers and mitigates the effects of insecticides in honeybees [43,44], bumblebees [45][46][47] and solitary bees [48,49].…”