Evidence of enhanced reproductive performance and lack-of-fitness costs among soybean aphids, Aphis glycines, with varying levels of pyrethroid resistance

Authors: VALMORBIDA, IVAIR - Iowa State University; Coates, Brad; HODGSON, ERIN - Iowa State University; RYAN, MOLLY - Corteva Agriscience; O'NEAL, MATTHEW - Iowa State University

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2022
Publication Date: 3/2/2022
Citation: Valmorbida, I., Coates, B.S., Hodgson, E.W., Ryan, M., O'Neal, M.E. 2022. Evidence of enhanced reproductive performance and lack-of-fitness costs among soybean aphids, Aphis glycines, with varying levels of pyrethroid resistance. Pest Management Science. 78(5): 2000-2010. https://doi.org/10.1002/ps.6820.
DOI: https://doi.org/10.1002/ps.6820

Interpretive Summary: Soybean aphids are severe pests of soybean across the Midwest United States that reduce crop yields by directly feeding on plants and spreading viruses that cause plant disease. Farmers use insecticide sprays to reduce damage and yield loss. Soybean aphids have developed resistance to pyrethroids, a commonly used and inexpensive class of insecticides. This resistance is associated with mutations that cause changes in a protein that conducts nerve impulses, the voltage gated sodium channel (VGSC). Most mutations that lead to resistance are assumed to have adverse effects on insect growth and reproduction. These effects are important to understand because, if they occur, they can hinder or delay the spread of resistance. An ARS scientist along with university and industry collaborators compared the fitness of aphids with different levels of pyrethroid resistance with aphids with no resistance. Results show that measures of growth and reproductive rates are not lower among resistance aphids with different VGSC mutations than those of susceptible aphids that lack VGSC mutations. In fact, one set of resistant aphids grew and reproduced faster than susceptible aphids. Data suggests that pyrethroid resistant aphids have no associated reductions in fitness compared to susceptible counterparts, and may partially explain their rapid spread across the Midwest. This research will be of interest to university, government, and industry stakeholders, as well as regulatory agencies interested in understanding the factors affecting the persistence and spread of insecticide resistance in insect pests.

Technical Abstract: Foliar application of insecticides remains the main strategy to manage soybean aphids, Aphis glycines (Hemiptera: Aphididae), in the northcentral United States. However, subpopulations of the A. glycines have evolved resistance to pyrethroids. Different mutations in the voltage-gated sodium channel (vgsc) gene are associated with pyrethroid-resistance. We determined the fitness costs associated with phenotypes conferred by these vgsc mutations using age-stage, two-sex life table analyses with field-collected parthenogenetic clonal female A. glycines. Significant differences were predicted in the pyrethroid susceptibility among A. glycines clones with differing vgsc genotypes. Estimated resistance ratios for the pyrethroid-resistant clones ranged from 3.1 to 37.58 and 5.6 to 53.91 to lambda-cyhalothrin and bifenthrin, respectively. Although life table analyses showed that some biological and demographic parameters were significantly different among the clonal lines, there was no association between levels of pyrethroid resistance and decline in fitness. In contrast, one of the most resistant clonal lines (SBA-MN1-2017) showed a significantly higher reproductive performance and a better overall fitness when compared to susceptible controls and other pyrethroid-resistant clonal line. Life history parameters of pyrethroid-resistance clones of A. glycines were not associated with negative pleotropic effects. Although evidence of any fitness costs associated with resistance were not predicted in this study, we discuss the potential impact of these results on efficacies of IRM and integrated pest management (IPM) plans directed at delaying the spread of pyrethroid-resistance A. glycines.