Influence of predation and parasitism on native coccinellid communities in Ohio agricultural landscapes

Lady beetles (Coccinellidae) are important natural enemies that provide valuable biological control services in many crops. Recently, observational studies have shown that native coccinellid species are declining in agricultural landscapes. Competitive interactions with exotic lady beetles such as intraguild predation of native eggs and larvae, have been proposed as a mechanism to explain this decline. To test this hypothesis, we examined the amount of egg predation incurred by native (Coleomegilla maculata) compared to exotic (Harmonia axyridis) lady beetles in three habitats: alfalfa, soybean, and grasslands. Eight replicates of each habitat were included in the study and sites were selected throughout Ohio, incorporating habitats within landscapes which varied in composition and heterogeneity. Within each site, the coccinellid population was surveyed using sweep netting and yellow sticky trap samples. Egg predation was assessed by determining the proportion of freeze-killed native and exotic lady beetle eggs removed by predators within 48 hr of exposure. To account for loss due to weather or other factors, we compared removal of eggs in masses open to attack by predators with those in clip cages. While rearing coccinellids to obtain egg masses, we observed very high rates of parasitism (approx. 61%), among field-collected C. maculata adults. Therefore, we also examined the rates of and responses to parasitoid attack of native and exotic lady beetles collected in our field sites. Once data collection is completed (September 2009) we will examine the influence of both habitat and large-scale landscape structure on the rates of egg predation and parasitism among exotic and native coccinellids.