The impact of ant populations on pecan aphids and associated beneficial insects in pecan orchards

Ants engage in both antagonistic and mutualistic interactions with honeydew-producing Sternorrhynchan insects, depending on the species involved and the ecological context. Ant foraging can also influence the abundance of insect herbivores and their associated natural enemies. A 2-yr field experiment (2023-2024) was conducted to evaluate the effects of ant exclusion on pecan aphids (yellow pecan aphid complex and black pecan aphid) and their associated natural enemies (lady beetles, lacewings, and long-legged flies) at 3 canopy heights (upper, middle, and lower). Seasonal trends in aphid abundance were generally similar between treatments across both years, and on most sampling dates; no treatment effects were detected for aphids or aphidophagous predators. However, on specific sampling dates, aphid abundance was lower in ant-excluded trees, and peak ant activity coincided with the aphid activity, suggesting that the strength of ant-aphid interactions varies with aphid population density. In contrast, parasitized aphid mummies were significantly more abundant on control trees in 2023. It was found that lady beetle and lacewing activity was higher and coincided with the peak activity during July and August. Additionally, long-legged flies were more abundant in ant-excluded trees during 2023 and were influenced by canopy height in both years. Collectively, these results indicate that ant exclusion can influence aphid-natural enemy interactions in pecan orchards, but these effects are episodic, natural enemy-specific, and variable by growing season.