Bats at risk? Bat activity and insecticide residue analysis of food items in an apple orchard

Abstract

Although bats are reported as being threatened by pesticides, they are currently not considered in European Union pesticide risk assessments. The reason for that contradiction is probably related to the scarcity of information on bat activity in pesticide-treated fields and the pesticide residues on their food items. The authors recorded bat activity and measured pesticide residues on bat-specific food items following applications of two insecticides in an apple orchard. High activity levels of the common pipistrelle bat, a foraging habitat generalist, were detected. Airborne foragers and bats that take part of their food by gleaning arthropods from the vegetation were recorded frequently. The initial value and the decline of pesticide residues were found to depend on the arthropod type, their surface to volume ratio, their mobility, and the mode of action of the applied pesticide. The highest initial residue values were measured on foliage-dwelling arthropods. By following the toxicity-exposure ratio approaches of the current pesticide risk assessment, no acute dietary risk was found for all recorded bat species. However, a potential reproductive risk for bat species that include foliage-dwelling arthropods in their diet was indicated. The results emphasize the importance of adequately evaluating the risks of pesticides to bats, which, compared to other mammals, are potentially more sensitive due to their ecological traits.