THE EFFECTS OF PREDATION ON SUGARCANE APHIDS IN SORGHUM

The sugarcane aphid, Melanaphis sacchari Zehntner (Hemiptera: Aphididae), is an emerging pest in sorghum, Sorghum bicolor (L.), in the USA. Lady beetles and green lacewings are abundant in sugarcane aphid-infested sorghum fields, but little is known about the effects of these predators on the establishment and growth of sugarcane aphid populations in sorghum. I quantified the effect of two species of lady beetles (Coccinella septempunctata L. and Harmonia axyridis Pallas) (Coleoptera: Coccinellidae) and green lacewings (Chrysoperla rufilabris Burmeister) (Neuroptera: Chrysopidae) on aphid colony growth across several aphid densities. I incorporated these predator effects into a dynamic predator-prey model to predict the impact of predators on the short-term population dynamics of sugarcane aphids and their ability to suppress aphids below action thresholds in sorghum. I also compared the effects of aphid-resistant sorghum on predation by lacewing larvae. All predators were able to significantly reduce the growth of sugarcane aphid populations at low to intermediate aphid densities (20, 40, and 80 aphids per colony). At the highest aphid density (160 aphids), H. axyridis larvae were much less effective and lacewing larvae did not suppress sugarcane aphid colony growth. The model found that all predators prevented aphid densities between 20-40 per leaf from reaching action thresholds and at densities of 80 aphids per colony, all predators suppressed aphids below threshold in two to four days. However, at the highest initial aphid density (160), H. axyridis larvae required seven days to suppress aphids below threshold and lacewing larvae never suppressed aphids below threshold. Aphid-resistant cultivars sustained smaller populations of aphids compared to susceptible. However, predators were an overall more effective tool to reduce aphid densities than use of only resistant varieties. As there is some evidence that predators may be more attracted to aphid-infested resistant varieties, predator effects may be enhanced on these varieties. My results suggest that common predators have the potential to reduce the number of insecticide applications needed to control sugarcane aphids and should be incorporated into Integrated Pest Management (IPM) programs. The simultaneous use of biological control and resistant varieties may yield synergistic suppression of sugarcane aphids in sorghum