Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphidae), a major pest of soybean in the Midwest U.S., is primarily controlled with insecticides, but aphid-resistant plants are becoming available for growers. However, aphid populations can still occasionally build to economically damaging levels on resistant plants, which require treatment with insecticides to protect yields. To determine if resistant plants alter soybean aphid susceptibility to foliar insecticides, aphid populations were monitored over two years from 2014 to 2015 in field experiments with near isogenic soybean lines that were either susceptible or resistant to aphids. Field plots of each soybean line were either untreated or treated with an organophosphate (i.e., chlorpyrifos), a pyrethroid (i.e., λ-cyhalothrin), or a mixture of pyrethrum and azadirachtin. Greenhouse bioassays were also conducted with near isogenic lines and two of the insecticides to examine potential interactions under more controlled conditions. In field plots, organophosphate and pyrethroid treatments significantly reduced cumulative aphid days on at least one soybean line each year; additive effects between resistant plants and insecticides were most common. However, significant synergistic interactions between resistant plants and insecticide were found for λ-cyhalothrin in 2015. On chlorpyrifos-treated plants, a synergistic interaction occurred in 2014 and an antagonistic interaction occurred in 2015, but aphid populations did not exceed those of untreated resistant plants. Interactions between aphid-resistant plants and foliar insecticides were variable, but these tactics generally appear compatible for integrated pest management programs. Growers could benefit from additive and synergistic interactions, and the only documented instance of antagonism had a relatively small effect.
Bibliographical noteFunding Information:
This research was supported by the North Central Region Sustainable Agriculture Research and Education (NCR-SARE) Program Graduate Student Grant ( GNC13-170 ) and the Minnesota Soybean Research and Promotion Council . This research was also supported by the University of Minnesota’s Doctoral Dissertation Fellowship. Funding sources were not involved in conducting the experiments or preparing this manuscript. We thank Kimon Karelis for planting and plot maintenance at the Rosemount Agricultural Experiment Station. We are also grateful for assistance with plot sampling from Wally Rich, Tavvs Alves, Anh Tran, Zach Marston, Erica Nystrom, Daniela Pezzini, Celia Silverstein, James Menger-Anderson, Traci Eicholz, Kathyrn Pawley, Annika Asp, Kealy Porter, Kylie Rich, Anderson Weber, and Crystal Dier.
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- Antagonistic effect
- Aphis glycines
- Rag gene
- Synergistic effect