Agricultural intensification may create an attractive sink for Dolichopodidae, a ubiquitous but understudied predatory fly family

Abstract

Long-legged flies (Dolichopodidae) are common within U.S. agroecosystems, but rarely the focus of ecological study. Given a documented sensitivity to environmental changes, at least in natural systems like grasslands and reed marshes, we aimed to determine how local management and landscape-scale factors might influence the community assemblage of Dolichopodidae found within vegetable farms. During the summer of 2013 and 2014, pan trapping was used to sample the long-legged fly community present in produce farms across the northeast region of the U.S. state of Ohio; farms were selected to represent gradients of landscape complexity and management intensity. Communities found within sweet corn, summer squash, and unmanaged old fields were surveyed. Over 3000 flies representing 11 genera and 33 species were collected. This adds an additional 4 genera and 19 species as occurring within the study region. In nearly all cases, we found that Dolichopodidae abundance and the diversity of genera collected was greater within vegetable crops versus set-aside habitats on farms. Within croplands, the value of a habitat patch for Dolichopodidae was highly dependent on agricultural intensification; fields with a high frequency of pesticide use and conventional tillage practices supported reduced abundance and diversity. Landscapes dominated by agricultural production were also found to reduce the species pool of Dolichopodidae found within sampled habitats. Our findings provide an important baseline of Dolichopodidae species and their relative abundance within regional agricultural landscapes. They also highlight the potential that highly attractive but intensively managed croplands may act as ecological traps, with consequences for Dolichopodidae conservation.