The effects of sugarcane aphid density in sorghum on predation by lady beetles and lacewings
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2018 Elsevier Inc. The sugarcane aphid, Melanaphis sacchari Zehntner (Hemiptera: Aphididae), is a new and devastating pest of sorghum (Sorghum bicolor (L.)) in the United States. Arthropod predators, especially lady beetles and green lacewings, are often abundant in sugarcane aphid-infested sorghum, but little is known about the effects of these predators on sugarcane aphid populations. We quantified the effect of two species of lady beetles (larvae and adults of Coccinella septempunctata L. and Harmonia axyridis Pallas) (Coleoptera: Coccinellidae) and green lacewings (larvae of Chrysoperla rufilabris Burmeister) (Neuroptera: Chrysopidae) on aphid colony growth across several aphid densities (20, 40, 80, 160). We found that all predator species and life stages significantly reduced 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), however, H. axyridis larvae were much less effective than C. septempunctata larvae and adults and H. axyridis adults and lacewing larvae did not suppress sugarcane aphid colony growth. We 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 in sorghum (214 days) and the ability of these predators to suppress aphids below action thresholds (5075 aphids per leaf). The model illustrated that all the predators we studied prevented aphid densities between 20 and 40 per leaf from reaching action thresholds. At initial densities of 80 aphids per colony, all predators were able to suppress aphids below threshold in two to four days. At the highest initial aphid density (160), however, H. axyridis larvae could not suppress aphids below the action threshold by four days and lacewing larvae never suppressed aphids below the threshold. Our results suggest that common predators in sorghum have the potential to suppress sugarcane aphid population growth and reduce the number of insecticide applications needed to control sugarcane aphids.
