Indirect plant defense may provide economically important pest suppression in sorghum

Authors: RUSSAVAGE, EMILY; HELMS, ANGEL - TEXAS A&M UNIVERSITY; THOMPSON, MORGAN - TEXAS A&M UNIVERSITY; SZCZEPANIEC, ADRIANNA - COLORADO STATE UNIVERSITY; ROONEY, WILLIAM - TEXAS A&M UNIVERSITY; KERNS, DAVID - TEXAS A&M UNIVERSITY; EUBANKS, MICKY - COLORADO STATE UNIVERSITY

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Since initial outbreaks in 2013, the sorghum aphid has caused extensive economic losses for sorghum growers throughout the United States. This sap-feeding insect can reduce grain quality and yield and, if left uncontrolled, can cause plant death. Crop breeders have already developed partially resistant sorghum cultivars that directly affect aphid physiology. We have previously identified chemical plant traits that attract insect predators and parasitoids; however, whether these traits play a role in aphid control is unknown. In this two-year field study, we successfully identified a sorghum cultivar that both reduced aphid reproduction and attracted higher densities of insect predators and parasitoids. As a result, no insecticide sprays were required to manage aphids on this cultivar, which has the potential to save growers time and costs associated with aphid management. Our findings demonstrate that both trait types deliver substantial pest suppression and provides a new suite of traits to incorporate into crop improvement and breeding programs.

Technical Abstract: 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 parasitoids and emitted more chemical attractants than two other cultivars. In this field study, we manually infested nine-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 estimate the effects of natural enemies 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 compared to 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, however, 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 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.