Project Details:

Extension and research to combat insecticide resistant soybean aphids

Parent Project: This is the first year of this project.
Checkoff Organization:Iowa Soybean Association
Categories:Insects and pests
Organization Project Code:
Project Year:2018
Lead Principal Investigator:Erin Hodgson (Iowa State University)
Co-Principal Investigators:
Keywords: Insecticide Resistance, Soybean Aphid (SA), Soybean Aphid - Monitoring

Contributing Organizations

Funding Institutions

Information and Results

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Project Summary

Growing evidence indicates that soybean aphid is developing field-evolved resistance to several pyrethroid insecticides. Pyrethroid resistance was first confirmed in several fields in southern Minnesota during 2015 by Bob Koch (University of Minnesota). Since then, pyrethroid resistance was also confirmed in one field in northwest Iowa in 2016 by Erin Hodgson (PI). Data which confirmed resistance in commercial soybean fields in Minnesota and Iowa is submitted for peer review.

Since the establishment of soybean aphid in the U.S., foliar insecticide use on soybean has increased by 130% (Ragsdale et al. 2011). From 2000-2015, foliar insecticides performed well, often reducing populations by 95-99% and protecting yield. Pyrethroids are a popular choice for soybean aphid management because the products have excellent efficacy and were relatively inexpensive. However, pyrethroid-resistant aphids will complicate management practices and farmers could expect a yield loss of 25-40% when ineffective tools are used. The challenge for managing soybean aphids in light of pyrethroid resistance is two-fold: 1) identify the geographic range of pyrethroid-resistant soybean aphids in Iowa; and 2) limit the spread of resistant populations with appropriate tools. Meeting this challenge will require offering sustainable management practices to farmers and the Ag industry.

We propose a series of objectives that would identify where insecticide-resistant aphids are found in Iowa, describe the mechanism of this resistance, and develop a diagnostic tool for rapid confirmation of pyrethroid-resistance. Thanks to previous Soybean Checkoff funding, we are able to exploit resources like the soybean aphid genome and to conduct this research. We assembled a team of University (Hodgson, O’Neal, Coats) and USDA (Coates) scientists to complete these objectives.

Project Objectives

OBJECTIVE 1. Landscape assessment of pyrethroid resistance in Iowa
OBJECTIVE 2. Understanding the mechanism of resistance
OBJECTIVE 3. The genetic basis of pyrethroid resistance and diagnostic molecular assays
OBJECTIVE 4. Extension

Project Deliverables

• Raise awareness of pyrethroid resistance among farmers and ag industry [short term knowledge];
• Implement scouting and adopt economic thresholds for soybean pests [long term skill];
• Recognize options for managing soybean aphid, including alternative insecticides, host plant resistance, etc. [long term knowledge];
• Reduce insecticide use, including seed and foliar treatments [long term skill];
• Understand the implications of soybean aphid genetic resistance to insecticides [long term knowledge]; and
• Improve profit margins by reducing input costs [long term knowledge].

Progress of Work

Updated April 11, 2018:
Soybean aphids are the most significant insect pest of soybean in Minnesota, Iowa, North Dakota and South Dakota. Development of insecticide resistance in this pest creates new challenges for effective soybean pest management and profitable soybean production. Failures of certain pyrethroid insecticides for management of some soybean aphid populations have been observed in commercial fields, and resistance to bifenthrin and lambda-cyhalothrin has been documented through small-plot research and laboratory bioassays. Because of the mobility of winged soybean aphids, the challenges posed by insecticide-resistant populations of the pest could spread to soybean fields in other parts of the region.

If a field needs to be retreated due to a failure, rotate to a different insecticide group for the follow-up application. For example, if a field was treated with a pyrethroid (Group 3A) and a follow-up insecticide application is needed, then an insecticide from different insecticide group, such as an organophosphate (Group 1B), should be selected. Mixtures of insecticides (premixes or formulated mixtures) may be effective for pest suppression but generally are not preferred for insecticide resistance management. Insecticide seed treatments are not a viable answer to managing insecticide resistant aphid populations.

Until aphid-resistant soybean varieties and other management tactics become more widely available, cost-effective management of soybean aphid will continue to rely on scouting and threshold-based insecticide applications of the few labeled insecticide groups. This short list of insecticide groups is under threat of becoming even shorter through continued development of pest resistance to insecticides and potential regulatory actions. The agricultural community would be wise to work together to preserve the effectiveness of and continued access to these important tools for protection of crops from insect pests.

View uploaded report PDF file

View uploaded report 2 PDF file

Final Project Results

Updated February 13, 2019:
Soybean aphid populations throughout Iowa were lower than in 2017. As a result, few commercial fields were sprayed and we did not respond to any “performance failures” this summer. The lack of reports does not mean pyrethroid-resistant aphids were absent in Iowa.

Dose response analyses were performed to evaluate the susceptibility of soybean aphid populations to lambda-cyhalothrin, an insecticide used to control aphids in soybean. Three laboratory populations (Biotypes 1, 3, 4) and three field populations (Sutherland, Minnesota colonies 1 and 2) collected in the Summer of 2017 were screened using leaf dip bioassay as recommended by the Insecticide Resistance Action Committee (IRAC), and LC50 and resistance ratios were calculated. Results indicate no variation in the susceptibility between biotypes 1 and 3; however, the LC50 of biotype 4 was almost twice as the LC50 of Biotypes 1 and 3. Field-collected populations also demonstrated different susceptibility to lambda-cyhalothrin when compared to the Biotype 1 colony (hereafter as susceptible colony). The population from Sutherland, IA, had a resistance ratio of 3.7. The two Minnesota colonies had similar LC50s and resistance ratios of 45.8 and 36.65, respectively.

View uploaded report Word file

Exceptional progress was made in 2018 regarding developing a protocol to evaluate pyrethroid resistance for soybean aphid. We are using a combination of lab and growth chambers experiments on several lab colonies. In addition, we are preparing to use molecular genetic techniques to describe how insecticide resistance is developing for soybean aphid.

Benefit to Soybean Farmers

Farmers can lose money several ways from insecticide-resistant aphids, including: 1) paying for an insecticide that does not work; 2) losing soybean yield to the aphid; and 3) paying for additional insecticide applications that are effective. If an effective insecticide is not applied quickly, farmers may experience the worse possible situation- paying for inputs that ultimately do not prevent yield loss; ultimately that could be $5-20 per acre in input costs and 20-40% reduction in yield. Completing this project would ultimately prevent the loss of time, money and yield.

Performance Metrics

Although we are too early into the project to evaluate the direct impact to farmers, Erin Hodgson is dedicating time to raising awareness of pyrethroid resistance for soybean aphid in Iowa and the north central region. She co-wrote three publications, of which two were regional efforts. The publications will reach farmers, crop consultants and ag industry folks to help them understand the significance of this resistance issue. Erin is also investigating alternative modes of action to provide effective options for soybean aphid management. Matt O'Neal and Erin continue to work on host plant resistance for soybean aphid, including using pyramids to reduce the likelihood of insecticide use to protect yield. All of these tools will ultimately improve profit margins in soybean by reducing the negative impact of soybean aphid.

Project Years