Lady Beetle (Coleoptera: Coccinellidae) Communities in Soybean and Maize

Coccinellids provide the most effective natural control of soybean aphid, but outbreaks remain common. Previous work suggests that native coccinellids are rare in soybean, potentially limiting soybean aphid control. We compared the coccinellid community in soybean with that of maize to identify differences in how coccinellid species use these habitats. As maize has long been used by coccinellids in the Americas, we hypothesized that coccinellids native to the Americas would use maize habitats, while exotic coccinellids would be more common in soybean. We identified and quantified aphids and all species and stages of coccinellids in a randomized complete block experiment with four blocks of 10 by 10-m plots of soybean and maize in central Minnesota during 2008 and 2009. Coccinellid egg masses were identified by hatching in the laboratory. We used repeated-measures ANOVA to identify the dominant species in each habitat and compared species richness and Shannon's diversity with a paired t-test. Aphids and coccinellids had a similar phenology across habitats, but the coccinellid species composition differed significantly between soybean and maize. In soybean, the exotic, Harmonia axyridis Pallas, was the dominant species, while in maize, H. axyridis and the native, Coleomegilla maculata De Geer, were co-dominant. Eggs of H. axyridis were abundant in both habitats. In contrast, C. maculata eggs were very rare in soybean, despite being abundant in adjacent plots of maize. Species diversity was higher in maize. These findings were consistent with other published studies of coccinellid communities in these habitats.