Investigating effects of surrounding landscape diversity on populations of Japanese beetles in Iowa soybean

The landscape around a field can influence the abundance and diversity of the community of insects within it. Understanding the relationships between surrounding landscapes and pest abundance can inform management decisions by determining which fields may be at greatest risk for a pest outbreak. For example, soybean aphids, Aphis glycines Matsumura (Hemiptera: Aphididae), have both a lower abundance and a higher occurrence of biological control in soybean fields within high diversity landscapes. Unlike A. glycines, Japanese beetles, Popillia japonica Newman (Coleoptera: Scarabaeidae) are highly polyphagous and have relatively few native natural enemies. Therefore, the relationship between their abundance in soybean fields and the surrounding landscape may be different than that of A. glycines. In 2012, we initiated a study to determine the effects that surrounding landscape diversity may have on the seasonal abundance of this pest in soybean. To evaluate this relationship, we sampled Japanese beetles in soybean fields surrounded by landscapes with a high degree of diversity (>50% non-crop habitat) and fields surrounded by landscapes with lower amounts of diversity (<10% non-crop habitat) within a 2 km buffer around each field. During the 2012 and 2013 field seasons, we identified fields within each type of landscape in three separate Iowa counties. The seasonal abundance of Japanese beetles was determined by direct observation and sweep net sampling. Results of this sampling showed that significantly higher seasonal abundances occurred in soybean fields surrounded by high diversity landscapes than in fields surrounded by low diversity landscapes.