Aphids on soybean leaves.

2020-21 Rapid Ag: Insecticide Resistance Management for Soybean Aphid: Understanding Biological Mechanisms and Grower Practices

April 9, 2019

Principal Leader

Robert Koch

Department

Entomology

The Problem

Soybean aphid, an invasive species from Asia, is the most significant insect pest of soybean in Minnesota and the U.S. Current management programs for soybean aphid are threatened by the pest’s recent development of resistance to pyrethroid insecticides. Our research- and extension-focused team was the first to identify soybean aphid resistance to insecticides in North America, but the biological mechanisms conferring resistance and grower knowledge and practices related to it remain unknown. Research-based knowledge on both of these factors will be essential for developing effective insecticide resistance management programs to ensure long-term, effective pest management. We propose to identify the biological mechanisms that confer pyrethroid resistance in the soybean aphid, elucidate the statewide prevalence of resistance in soybean aphid, and gather data from growers to support the development of innovative strategies to improve management of this pest.

Background

Soybean aphid, Aphis glycines Matsumura, is the most significant insect pest of U.S. soybean, Glycine max (L.) Merr., causing up to 40% yield reductions (Ragsdale et al. 2011). Extensive research has been conducted on non-chemical tactics for soybean aphid management (Ragsdale et al. 2011); however, aphid-resistant soybean varieties remain relatively unavailable to growers (Hanson et al. 2016) and biological control with parasitic wasps may have only a minor impact on soybean aphid populations (Leblanc & Brodeur 2018). Therefore, management of soybean aphid continues to rely primarily on the use of foliar-applied insecticides from only three insecticide groups (Groups 1, 3 and 4), which has created a situation ripe for development of insecticide resistance (Koch et al. 2018).

Koch’s laboratory provided the first evidence for soybean aphid resistance to insecticides in North America (Hanson et al. 2017). Geographically, field failures of pyrethroids (bifenthrin and lambda-cyhalothrin) and confirmed resistance through laboratory bioassays are now known to include Minnesota, Iowa, North Dakota, South Dakota, and Manitoba (Hanson et al. 2015, Koch et al. 2018) (Fig. 1). Pyrethroid resistance in other insects has been associated with mutations in the Na-channel (para)gene (Martinez- Torres et al. 1997,1999; MacKenzie et al. 2018) and overexpression of detoxification enzymes (Coppin et al. 2012). However, the mechanisms and underlying genetic basis of pyrethroid resistance in soybean aphid in North America is unknown.

The recent occurrence of resistance to pyrethroids in soybean aphid has created an immediate challenge for effective pest and resistance management and profitable soybean production, because 1) few insecticide groups are available for soybean aphid management and 2) non-chemical management tactics are relatively unavailable (as described above). The direct costs incurred by growers from insecticideresistant soybean aphid include yield losses due to poor insecticide efficacy and the costs of additional insecticide applications to compensate for poor insecticide performance. An additional important, but less tangible, consequence of soybean aphid insecticide resistance is its effect on insecticide application decision-making. Insecticides are now being applied in a way that is likely increasing selection for continued and higher resistance in soybean aphid and further threatening an already short list of management tools (Koch et al. 2018).

To rapidly respond to the challenges posed by insecticide-resistant soybean aphids, we propose a multidisciplinary approach. The knowledge gained on the mechanisms by which the aphids overcome insecticides (Horowitz and Denholm 2001) and grower decision-making for insecticide use (Hurley and Mitchell 2013, Hawkins et al. 2018) will be essential for the development of robust insecticide resistance management (IRM) programs. Results of this project will mitigate the threat posed by insecticide resistance to the economic and environmental sustainability of soybean production.

Goals and Objectives

  1. Identify mechanisms of soybean aphid resistance to pyrethroids -  (a) Identify detoxification enzymes involved in soybean aphid resistance to pyrethroids; (b) Determine genetic variation in sodium channel genes associated with soybean aphid resistance

  2. Assess the prevalence of pyrethroid resistance in Minnesota soybean aphids - (a) Quantify survival of field-collected populations of soybean aphid in laboratory bioassays; (b.) Quantify expression levels of detoxification enzymes and frequency of sodium channel gene mutations in field-collected populations of soybean aphid; and, (c) Determine soybean grower attitudes and practices related to insecticide-resistant soybean aphids

References

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  • Hawkins et al. 2018. Biological Reviews. https://doi.org/10.1111/brv.12440. Hanson et al.. 2016.
  • Aphid-resistant soybean varieties for Minnesota. University of Minnesota Extension. (https://extension.umn.edu/crop-production/aphid-resistant-soybean-variet...).
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