Effect of canopy height and prey location on lady beetle (Coleoptera: Coccinellidae) captures in soybean

In the absence of aphid migration events, lady beetles are capable of suppressing soybean aphid populations below economic injury levels in much of the North Central US. Several factors may influence their ability to locate suitable prey patches, including abiotic factors like wind direction or speed, or biotic factors like prey availability, location, or even quality. For soybean aphid, within-plant distributions change throughout the season but the reasons for these shifts are unclear. The goal of this research was to evaluate how coccinellid communities respond to differing aphid populations within a changing soybean canopy. In a early-planted and double-cropped soybean field, 40 randomly selected plants were enclosed using a 1-2 m tall wire cylinder covered with mesh and coated in tangle foot (sticky cylinders). This cylinder design allowed us to passively record height and direction for all lady beetle captures in response to four aphid treatments. These included two controls (a plant with no aphids and a cylinder with no plant) and plants with aphids restricted to upper or lower canopy using leaf exclusion cages. Although aphid location within the canopy varied, aphid density was kept consistent between treatments. Changes in coccinellid communities were calculated using the Shannon-Weaver index and rank-proportion between fields and treatments. In general, we found that early-planted soybeans had the same species richness, but lower evenness when compared to double-cropped soybeans. Furthermore, using logistic regression, lady beetle captures were positively correlated with changes in canopy height but did not display any patterns of directionality.