Combined exposure to sublethal concentrations of an insecticide and a fungicide affect feeding, ovary development and longevity in a solitary bee

Abstract

Pollinators in agroecosystems are often exposed to pesticide mixtures. Even at low concentrations, the effects of these mixtures on bee populations are difficult to predict due to potential synergistic interactions. In this paper, we orally exposed newly emerged females of the solitary bee to environmentally realistic levels of clothianidin (neonicotinoid insecticide) and propiconazole (fungicide), singly and in combination. The amount of feeding solution consumed was highest in bees exposed to the neonicotinoid, and lowest in bees exposed to the pesticide mixture. Ovary maturation and longevity of bees of the neonicotinoid and the fungicide treatments did not differ from those of control bees. By contrast, bees exposed to the pesticide mixture showed slow ovary maturation and decreased longevity. We found a synergistic interaction between the neonicotinoid and the fungicide on survival probability. We also found an interaction between treatment and emergence time (an indicator of physiological condition) on longevity. Longevity was negatively correlated to physiological condition only in the fungicide and the mixture treatments. Delayed ovary maturation and premature death imply a shortened nesting period (highly correlated to fecundity in). Our findings provide a mechanism to explain the observed dynamics of solitary bee populations exposed to multiple chemical residues in agricultural environments.

Are honeybees suitable surrogates for use in pesticide risk assessment for non‐Apisbees?

“…Although non‐ Apis data for acute oral toxicity are available in the literature, they are generally less robust than contact toxicity data, often being reported as being conducted in accordance to OECD guidelines, while in fact deviating significantly from the established protocols, e.g. continuous exposure or no measurement of consumption . Data from Bombus spp.…”

“…continuous exposure or no measurement of consumption. 48,[50][51][52][53] Data from Bombus spp. represent the majority of reliable non-Apis acute oral toxicity data because these are most readily dosed under laboratory conditions and an OECD guideline for oral toxicity in Bombus spp.…”

Do novel insecticides pose a threat to beneficial insects?

“…Methods that measure the fecundity of commercially available solitary bees (e.g. Osmia bicornis) after exposure to novel insecticides are an obvious candidate for the regulatory process owing to their availability, and importance in agriculture [97,98]. These suggested changes to the regulatory process are not necessarily novel (e.g.…”

“…However, likely stressors, such as nutritional stress, could easily be introduced to current and proposed methodologies (see §4a) used within the regulatory process [54]. Likewise, testing the interactions between insecticides and other agrochemicals such as fungicides and herbicides, especially those that are used in the same commercial formula, can be easily conducted with other commonly used methodologies [49, 55,97]. Testing the potential interactions between agrochemicals and pathogens is also important, but the sheer number of insect pathogens similarly makes it unfeasible to test all possible interactions.…”

Modeling the synergistic effects of toxicant mixtures

“…Other groups of organisms also showed combined synergistic effects in both field and laboratory studies. These included bees [11][12][13], the bacteria Vibrio fischeri [14], and crustaceans [14,15]. Toxicant mixtures showing synergistic effects include cholinesterase inhibitors, pyrethroids, azole fungicides and antifoulants [16].…”