Effects of the Invasive Ant Solenopsis invicta (Hymenoptera: Formicidae) on Menochilus sexmaculatus (Coleoptera: Coccinellidae) as a Predators of Aphis craccivora (Hemiptera: Aphididae) in Laboratory Conditions

The exotic fire ants Solenopsis invicta are aggressive, destructive invaders and have a significant impact on the arthropod community of an invaded area. Unfortunately, few studies have examined the impact of fire ant-aphid mutualism on ladybird beetles, which are primarily aphid-eating predators. In addition, the mechanisms of how both the odor trail and the aggressive behavior of fire ants disturb the ladybird predation of aphids have not been studied. Our study aims to resolve these questions through laboratory experiments. The results of this study demonstrate that fire ants are strongly attracted to aphids; consequently, the association between fire ants and aphids affects the different developmental stages of ladybirds on the same host plant. In the presence of fire ants, the amount of the early instar larvae, late instar larvae, and adults of ladybirds preyed upon were reduced by 98.3%, 94.6%, and 98.2%, respectively. More seriously, the ladybird larvae rarely survived. In contrast, ladybird adults usually chose to fly away when they were attacked by fire ants. The odor trail of fire ants did not influence the ladybird larvaes' predation of aphids, whereas the aggressive behavior of the fire ants did. We observed that the mean number of aphids that was preyed upon by early instar larvae, late instar larvae, and adult ladybirds was reduced by 30.5%, 45.5%, and 63.7%, respectively in laboratory experiments. We suggest that a high population density of fire ants may 1) change the spatial-distribution patterns of insect pests and natural enemies and 2) deeply affect insect pest management in agroecosystems.