Indirect plant defense may provide economically important pest suppression in sorghum

A promising strategy to optimize biological control of insect pests is selecting crop varieties with indirect defense traits. Indirect plant defenses recruit natural enemies to kill pests and include chemical attractants like herbivore-induced plant volatiles. In prior laboratory assays, we found sorghum (Sorghum bicolor L.) cultivar ATx3409/RTx436 infested with sorghum aphid (Melanaphis sorghi Theobald) was attractive to natural enemies and emitted more chemical attractants than two other cultivars. In this field study, we manually infested 9-week-old sorghum plants with aphids and quantified differences in natural enemy and aphid densities among cultivars throughout the growing season. We also used field cages to control access of natural enemies to plants and estimate their effects on aphid suppression.

We found strong evidence that indirect plant defenses confer economically relevant control of aphid pest populations and that laboratory assays can accurately predict natural enemy recruitment in the field. In 2022, there were three times more lady beetles (Coleoptera: Coccinellidae), lacewings (Neuroptera: Chrysopidae and Hemerobiidae), hover flies (Diptera: Syrphidae), and parasitoids (Hymenoptera: Braconidae and Aphelinidae) per aphid on ATx3409/RTx436 than on the other two cultivars. In the field cage experiment, natural enemies reduced aphid densities by up to 83% one week after aphid infestation. ATx3409/RTx436 was the only cultivar to remain below the economic threshold throughout the growing season, indicating that this cultivar would not require any pesticide applications to control aphids. In 2023, there were similar abundances of natural enemies and aphid densities across cultivars, the latter of which remained near zero throughout the growing season, likely due to extremely hot temperatures and drought that may have contributed to aphid mortality.

Our findings demonstrate that indirect plant defenses enhance biological control and deliver economically important pest suppression. Cultivar screening and selection for indirect defense traits provides a promising avenue to improve crop protection and breeding for resistance. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.