Abstract
There is widespread concern regarding the effects of agro-chemical exposure on bee health, of which neonicotinoids, systemic insecticides detected in the pollen and nectar of both crops and wildflowers, have been the most strongly debated. The majority of studies examining the effect of neonicotinoids on bees have focussed on social species, namely honey bees and bumble bees. However, most bee species are solitary, their life histories differing considerably from these social species, and thus it is possible that their susceptibility to pesticides may be quite different. Studies that have included solitary bees have produced mixed results regarding the impact of neonicotinoid exposure on survival and reproductive success. While the majority of studies have focused on the effects of adult exposure, bees are also likely to be exposed as larvae via the consumption of contaminated pollen. Here we examined the effect of exposure of Osmia bicornis larvae to a range of field-realistic concentrations (0–10 ppb) of the neonicotinoid clothianidin, observing no effect on larval development time, overwintering survival or adult weight. Flow-through respirometry was used to test for latent effects of larval exposure on adult physiological function. We observed differences between male and female bees in the propensity to engage in discontinuous gas exchange; however, no effect of larval clothianidin exposure was observed. Our results suggest that previously reported adverse effects of neonicotinoids on O. bicornis are most likely mediated by impacts on adults.
Highlights
Bees are important pollinators of crops and wild flowers, ongoing population declines and extinctions are a major cause for concern, considering increasing global reliance on insect-pollinated crops (Holden, 2006; Gross, 2008; Aizen & Harder, 2009)
Such declines are likely attributable to a number of factors, including habitat loss, How to cite this article Nicholls et al (2017), Larval exposure to field-realistic concentrations of clothianidin has no effect on development rate, over-winter survival or adult metabolic rate in a solitary bee, Osmia bicornis
Control (0 ppb) pollen provisions contained no neonicotinoid residues, and no neonicotinoids other than clothianidin were detected in samples from each of the treatment groups, confirming that pollen collected by females at the field site was free of neonicotinoids (Table 1)
Summary
Bees are important pollinators of crops and wild flowers, ongoing population declines and extinctions are a major cause for concern, considering increasing global reliance on insect-pollinated crops (Holden, 2006; Gross, 2008; Aizen & Harder, 2009). Laboratory studies have found the oral toxicity of neonicotinoids to be relatively high for bees (4–5 ng/honeybee, Suchail, Guez & Belzunces, 2001), and sub-lethal effects have been observed following exposure to concentrations within the range detected in field-collected pollen and nectar (reviewed in Alkassab & Kirchner, 2017) These effects include deficits in learning (Williamson & Wright, 2013; Stanley et al, 2015), foraging (Feltham, Park & Goulson, 2014; Gill & Raine, 2014) and homing ability (Henry et al, 2012), all of which are essential to bee survival and reproduction
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