Insects moving through forest-crop edges: a comparison among sampling methods

Abstract

Edges between natural and cultivated habitats have become dominant elements of all terrestrial ecosystems. Interchanges of several groups of organisms, such as insects, occur through these edges, potentially affecting ecosystem functioning and conservation of species and communities of neighboring habitats. Different trap types are used for collecting moving insects, although their effectiveness and complementarity for sampling in edges were not previously analyzed. Here, we evaluated the assemblages collected with three commonly used trap types (flight interception—FITs, yellow pan, and pitfall traps) at the boundaries between soybean fields and native forests in Central Argentina. We compared trap types from a taxonomic and functional perspective and determined their complementarity (how different assemblages were). In total, 66,949 arthropods from 1007 species were collected. Yellow pan traps collected more species and individuals, followed by FITs and pitfall traps. Pan traps and FITs showed low complementarity, whereas both types of traps were complementary to assemblages from pitfall traps. Yellow pan traps were also linked to higher species richness of most functional groups, whereas abundances and functional composition showed different patterns. Pan traps were linked to herbivores and natural enemies, and FITs with detritivores and, to a lesser extent, pollinators. These results suggest that the combination of pitfall traps with a trap for flying insects could provide a better representation of insect communities moving through edges. The choice between pan and FITs will be related to the main groups of interest, the costs and simplicity of use, and the relevance of quantifying directional movement.