Interactive effects of crop variety, insecticide seed treatment, and planting date on population dynamics of sugarcane aphid (Melanaphis sacchari) and their predators in late-colonized sorghum

Sugarcane aphids Melanaphis sacchari (Zehntner) (Hemiptera: Aphididae) have recently become an eruptive and costly pest of sorghum, Sorghum bicolor (L). In contrast to its southern range in the United States, sugarcane aphid colonizes sorghum at flowering or just post-bloom in the central High Plains. Thus the goal of this work was to quantify how sorghum resistance (commercially available hybrid DKS37-07), timing of planting (early or conventional plant date), and insecticide seed treatment (clothianidin) affected population dynamics of sugarcane aphids in late-colonized sorghum in the central High Plains. The impacts of these factors on sugarcane aphid densities were measured over two growing seasons, and the numbers of natural enemies of the aphids were quantified as well. Host plant resistance emerged as the main driver of sugarcane aphid population dynamics while planting date and seed treatment had a variable impact on M. sacchari and their predators. Host plant resistance also affected predators of sugarcane aphids and, while not directly explored in this study, potentially altered predator-aphid interactions as well. Diverse natural enemies including Coccinellidae, Syrphidae, Chrysophidae, and Anthocoridae were readily recruited by sugarcane aphid infestations, and predators were strongly correlated with populations of M. sacchari regardless of the seed treatment application or sorghum variety and across planting dates. This research demonstrates that a commercially available resistant sorghum variety provides the most robust protection against this pest in the central High Plains. Further, an already present assemblage of aphid predators recruits readily to aphid-infested sorghum and is likely to provide important biological control services particularly in resistant sorghum.