Insectivorous bats foraging in cotton crop interiors is driven by moon illumination and insect abundance, but diversity benefits from woody vegetation cover

Abstract

Landscape and biophysical determinants of insectivorous bat activity and community composition in space and time are central to understanding how growers can maximise bat-mediated pest control services in crops. We measured community composition, abundance, richness and foraging attempts of insectivorous bats in the centre of dryland cotton crops using acoustic sampling. We examined how bat activity was related to woody vegetation in the surrounding landscape, prey insect abundance, distance to crop edge, size of field, proximity to waterbodies and moon illumination to better understand insectivorous bat diversity and foraging in crop interiors. We collected a total of 9467 acoustic files including 1198 foraging attempts (feeding buzzes) of at least 21 insectivorous bat species. The bat assemblage in cotton crop interiors (richness and diversity) was positively related to woody vegetation foliage cover within 5-10 km of the crop, as well as Lepidoptera and Hymenoptera abundance, but was negatively related to distance from the field edge into the crop and moon illumination. Increased feeding attempts were linked to increased Lepidoptera and Hemiptera on nights of high moon illumination (> 75%). Bat activity and foraging was also higher during nights of increased insect abundance, particularly Lepidoptera, indicating that bats track food resources. Our results highlight the importance of managing bat roosting habitat at different landscape scales to enhance bat diversity and foraging in crop interiors and thus insect consumption. Given the high bat feeding activity on nights of high moon illumination and increased Hemiptera abundance, the timing of insecticide sprays to target pests, such as Hemipteran sucking bugs, could be scheduled on nights of low moon illumination. Such information is useful in identifying conservation priorities for the management of bats in intensively farmed agroecosystems and should facilitate habitat management by growers to maximise crop pest protection services in crop interiors.