Abstract
Currently, more than 360 spray adjuvants are registered in Germany (September 2021). Unlike plant protection products (PPPs), adjuvants are not subjected to regulatory risk assessment. In practice, numerous combinations of PPPs and adjuvants are therefore possible. Thus, tank mixtures containing insecticides that are classified as non-hazardous to bees up to the highest approved application rate or concentration may raise pollinator safety concerns when mixed with efficacy increasing adjuvants and applied in bee-attractive crops. This study analyzes whether selected “PPP–adjuvant” combinations result in increased contact mortality and pose an elevated risk to honey bees. To answer this question, we chose six common spray adjuvants of different classes for laboratory screening. These were then tested in a total of 30 tank mixtures, each with a neonicotinoid (acetamiprid), pyrethroid (lambda-cyhalothrin), diamide (chlorantraniliprole), carbamate (pirimicarb), and butenolide (flupyradifurone) formulation. We adapted an acute contact test (OECD Test Guideline 214) to our needs, e.g., by using a professional spray chamber for more realistic exposures. Our results showed that, in total, 50% of all combinations significantly increased the mortality of caged honey bees in comparison with individual application of insecticides. In contrast, none of the adjuvants alone affected bee mortality (Cox proportional hazard model, p > 0.05). With four of the five insecticide formulations, the organosilicone surfactant Break-Thru® S 301 significantly increased bee mortality within 72 h (for all insecticides except chlorantraniliprole). Furthermore, acetamiprid yielded the highest and second highest mortality increases from a tank mixture with the crop oil surfactant LI 700® (hazard ratio = 28.84, p < 0.05) and the organosilicone Break-Thru® S 301 (hazard ratio = 14.66, p < 0.05), respectively. To assess risk in a more field-realistic setting, field trials should be performed to provide a more realistic exposure scenario under colony conditions.
Highlights
Multiple factors, such as pathogens, parasites, loss of habitat, malnutrition, and the use of plant protection products (PPPs), are currently suspected to be causes of pollinator decline, which is being discussed globally (vanEngelsdorp1 3 Vol.:(0123456789)Journal of Plant Diseases and ProtectionWhen investigating these sublethal effects, it became increasingly apparent that adjuvants believed to be “inert” (EPA 2021) can have potentially toxic effects on bees (Goodwin and McBrydie 2000; Zhu et al 2014; Chen et al 2019)
We focused on insecticide formulations because a potential increase in efficacy there is likely to pose a higher risk to non-target organisms such as bees compared to other PPP groups due to their mode of action
The five selected insecticides (Figs. 2, 3, 4, 5, 6) were used as a reference in each case instead of the controls to measure the magnitude of mortality increase associated with the spray adjuvant
Summary
Multiple factors, such as pathogens, parasites, loss of habitat, malnutrition, and the use of plant protection products (PPPs), are currently suspected to be causes of pollinator decline, which is being discussed globally (vanEngelsdorp1 3 Vol.:(0123456789)Journal of Plant Diseases and ProtectionWhen investigating these sublethal effects, it became increasingly apparent that adjuvants believed to be “inert” (EPA 2021) can have potentially toxic effects on bees (Goodwin and McBrydie 2000; Zhu et al 2014; Chen et al 2019). Tank mixes can increase total mortality in honey bees in predictable (Pilling and Jepson 1993; Iwasa et al 2004; Wernecke et al 2019) and unpredictable ways (Johnson et al 2013; Zhu et al 2014; Wade et al 2019). Despite their relevance under normal field conditions, these aspects of pesticide toxicology are often overlooked (Chmiel et al 2020). Foragers are confronted with numerous spray adjuvants in the field (Ciarlo et al 2012; Mullin et al 2015; reviewed in Iwasaki and Hogendoorn 2021)
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