Common agricultural landscape elements serve as predictors of Melanaphis sorghi and natural enemy abundance: Implications for areawide pest management in a sorghum agroecosystem

The sorghum aphid, Melanaphis sorghi Theobald (Hemiptera: Aphididae), is an invasive pest that has rapidly expanded across the southern United States and northern Mexico since its detection in 2013. Natural enemies (predators and parasitoids) play a key but spatially variable role in biological control. This study investigated relationships between landscape elements and the abundance of M. sorghi and its natural enemies across commercial sorghum fields in the Texas Gulf Coastal Plains ecoregion. Weekly insect sampling was conducted using a two-leaf method, and landscape metrics were derived from cropland data layer classifications within 2.5 km buffers around each sampled field (derived from USDA NASS CropScape and managed in a GIS). Regression and stepwise model selection were used to assess associations between aphid and natural enemy counts and landscape metrics calculated (FragStats) from six landscape elements: sorghum, cotton, corn, grassland/shrubland/pasture, wetland, and fallow. Some metrics, including fragmented (small) sorghum plantings and increased diversity of these elements, were indicators of elevated aphid risk. Others, including fragmented corn plantings and aggregated (large) fallow cropland were indicators of heightened natural enemy activity. In contrast, classic percent composition of these elements (crop or noncrop) were not useful indicators of aphid or natural enemy abundance. These findings highlight the value of using landscape-derived metrics to consider areawide pest management strategies and provide a spatially informed framework for predicting M. sorghi and natural enemy abundance across the south Texas sorghum agroecosystem.