Parasitoids and Predators of the Invasive Aphid Melanaphis sorghi Found in Sorghum and Non-Crop Vegetation of the Sorghum Agroecosystem

SIMPLE SUMMARY: The sorghum aphid is an invasive pest of grain sorghum in North America; their infestations when in high numbers can reduce grain sorghum yield. Fortunately, there are numerous beneficial insects such as parasitoid wasps, lady beetles, hoverfly and lacewing larvae that will feed on these aphids. These beneficial insects are naturally occurring in local habitats such as grasses and shrubs, Johnson grass, and cropland surrounding grain sorghum during and after sorghum production. The goal of this study was to estimate the relative effect of these habitats to serve as a source of natural enemies of the sorghum aphid in- and off-season of sorghum production. This study was conducted over two years and the results found that predators (lady beetles and their larvae, hoverfly and lacewing larvae) were most diverse in the habitat containing grasses and shrubs and most abundant during the sorghum-growing season. Parasitoid wasps were abundant across all habitat types during and outside of the sorghum-growing season. These results highlight the potential importance of persistence of natural enemies across vegetation types associated with their ability to manage sorghum aphid infestations. The natural enemies in these habitats are well positioned to play a role in suppressing sorghum aphid. ABSTRACT: Melanaphis sorghi (Theobald) (sorghum aphid), (=Melanaphis sacchari Zehntner) (Hemiptera: Aphididae), is an invasive pest of Sorghum bicolor (L.) in North America. Over 19 species of predators and parasitoids have been found to prey on M. sorghi. Natural enemies may reside in vegetation such as sorghum in cultivation (in-season) and persist after harvest (off-season), in Johnson grass (Sorghum halepense) (L.) and riparian areas consisting of shrubs and grasses, including Johnson grass. The objective was to assess the ability of these vegetation types to harbor M. sorghi natural enemies during and between annual grain sorghum production. Predator diversity was greatest in riparian vegetation in-season, with twelve species detected across seven families, and four orders of insects. Six lady beetle (Coleoptera: Coccinellidae) species were abundant in-season, and Cycloneda sanguinea (L.) persisted at relatively high abundance off-season. Parasitoid diversity was more limited (two primary parasitoids and one hyperparasitoid detected) with the primary parasitoids commonly detected. Aphelinus nigritus (Howard) (Hymenoptera: Aphelinidae), accounted for 85% and 57% of parasitoids in- and off-season, respectively. Aphelinus nigritus abundance was steady across the annual sorghum season in all vegetation types. Results from this study will inform land-management strategies on how diverse vegetations can play a role in the biological control of M. sorghi.