Project Details:

Title:
Extension and Research to Combat Insecticide Resistant Soybean Aphids

Parent Project: Extension and research to combat insecticide resistant soybean aphids
Checkoff Organization:Iowa Soybean Association
Categories:Insects and pests
Organization Project Code:450-49-02
Project Year:2019
Lead Principal Investigator:Erin Hodgson (Iowa State University)
Co-Principal Investigators:
Joel Coats (Iowa State University)
Matthew O'Neal (Iowa State University)
Keywords:

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 now published (Hanson et al. 2017).
Since the establishment of soybean aphid in the U.S., foliar insecticide use on soybean increased by 130% (Ragsdale et al. 2011). From 2000-2015, foliar insecticides performed well, often reducing populations by 95-99% and protecting yield (Hodgson et al. 2012). Pyrethroids are a popular choice for soybean aphid management because the products have excellent efficacy and were 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: produce a map with confirmed pyrethroid resistance in Iowa.
• Objective 2: understand the mechanism of resistance for soybean aphid.
• Objective 3: develop a diagnostic tool for timely treatment decisions of resistant aphids.
• Objective 4: provide farmers with recommendations to protect yield and minimize input costs.

Project Deliverables

Expected Stakeholder Deliverables and Outcomes:
• 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].

Realized Stakeholder Deliverables and Outcomes:
Matt O’Neal and Erin Hodgson organized a resistance management field day in August 2017 to raise awareness of pyrethroid resistance. Outcomes from the field day:
• Understanding SBA life cycle and biology had a 1,100% percent increase.
• Knowing SBA host plant resistance options had a 900% percent increase.
• Awareness of SBA insecticide resistance had a 700% percent increase.
• Implementing integrated SBA management had a 1,000% percent increase.
• Participants were asked about their perception of value, and 100% said it was a “very valuable” workshop. There were notable behavior changes indicated in the survey summary: 58% said they will consult with ISU regarding future pest management decisions and 44% said they will scout and use economic thresholds for SBA.
• In general, respondents indicated the four speakers contributed to a successful workshop. For example, 93% of people attending the workshop said Erin Hodgson had “excellent” energy, and 100% of people said Erin had “excellent” engagement with the group and were experts in their respective fields.

Progress of Work

Updated April 22, 2019:
Spring planting conditions throughout Iowa were first cold and wet in 2018, and most soybean fields were planted later to accommodate corn planting. Then May was warmer than normal and June turned exceptionally wet throughout most of Iowa. Population fluctuations between locations and years is typical soybean aphid dynamics for Iowa. Soybean aphids arrived on soybean in July, slightly behind average infestation dates. Soybean aphid colonization was initially patchy and continued to grow at a slow pace, likely due to hot evenings providing little relief to adults. Some commercial fields experienced exponential growth of soybean aphid after bloom, especially in northern Iowa. However, few fields in northwestern and northcentral counties had soybean aphid exceed the economic threshold. Some populations did persist until after seed set (R5–R6), but very quickly crashed at most locations by mid-September. When applications had sufficient coverage and applied at the labeled rate, efficacy for soybean was good (i.e., >95% knockdown within three days after application) throughout most of Iowa. I was able to complete proposed work, including research and extension related to soybean aphid management. I established a foliar insecticide efficacy evaluation at two locations in 2018 (northwest and northeast Iowa). I had 25+ treatments at each location. In addition to soybean aphid, Japanese beetle, bean leaf beetle and soybean gall midge were prevalent in some Iowa soybean fields. I ended up spending a lot of time responding to questions and concerns about soybean gall midge.

View uploaded report PDF file

Updated October 8, 2019:
Objective 1a. UPDATE: We collected aphids in three locations in Iowa and one in Minnesota this summer. Aphids were screened for insecticide resistance using a glass-vial bioassay treated with lambda-cyhalothrin and bifenthrin.

What it means for farmers: Insecticide resistant aphids are found in Iowa, and have been found every year since 2016. The amount of these aphids within a population is high enough to suggest that these traits are fixed and will not go away when insecticides are not used.

Objective 1b. UPDATE: Four pyrethroid-resistant colonies are being maintained in our laboratory since 2018. In addition, aphids collected this summer from the same locations specified on objective 1a are being kept in mini-colonies for further studies.

What it means for farmers: The Soybean Entomology Laboratory maintains a resource that is a value to agribusiness and scientist exploring the threat of insecticide resistance in the soybean aphid. We will continue to explore these colonies to determine the mechanism and means to manage soybean aphids as pyrethroid resistance spreads. We have shared these resources with agribusiness when requested.

Objective 2a. UPDATE: Leaf dip bioassays were performed using the soybean aphid colony most resistant to lambda-cyhalothrin and a susceptible population to lambda-cyhalothrin. The two colonies were compared for susceptibility to bifenthrin, flonicamid, flupyradifurone, sulfoxaflor, spirotetramat, and chlorpyriphos.

What it means for farmers: We have confirmed that lambda-cyhalothrin resistant aphids in Iowa. We are working to determine if these aphids are also resistant to other insecticides.

Objective 2b. UPDATE: The most resistant to lambda-cyhalothrin was used to evaluate for rapid metabolism /detoxication as a mechanism of pyrethroid resistance in soybean aphid using synergistics (Piperonyl butoxide (PBO), S,S,S-Tributyltrithiophosphate (DEF) and triphenyl phosphate (TPP)). The results obtained for the resistant population were compared to those from the lab-susceptible population.

What it means for farmers: There is the potential to manage pyrethroid-resistant soybean aphids with pyrethroids if a synergist is added. Such an addition could allow farmers to prevent outbreaks without having to switch to a different (any potentially more expensive) active ingredient. Our findings revealed that adding a synergist to a pyrethroid did not improve the efficacy when used against pyrethroid resistant soybean aphids. Because the synergist didn't work, metabolic detoxification is not a part of pyrethroid resistance in the soybean aphid. This suggests that cross-resistance is unlikely to other insecticides with different modes of action. Therefore, based on our data to date, we do not anticipate pyrethroid-resistant soybean aphids to be more resistant to insecticides like chlorpyrifos than susceptible aphids.

Objective 3a. UPDATE: Given the resistance to lambda-cyhalothrin identified in Objective 2, we sought to determine any genetic differences among these populations. We used a candidate gene approach to determine if previously described mutations in the voltage-gated sodium channel (VGSC), specifically, if knockdown (kdr) mutations were present in individual soybean aphids from each subpopulation. These kdr mutations change the amino acid sequence and are highly correlated with pyrethroid resistance in other insect species.

We designed primers and sequenced part of segment VI of domain II of the soybean aphid VGSC gene, successfully amplified, and gene fragments DNA sequenced. Comparison of VGSC DNA sequences from susceptible and resistant aphids showed the presence of a kdr mutation only in the Sutherland (Iowa), MN1, and MN2 resistant (RES) populations (Fig. 1). In the case of soybean aphids, all pyrethroid resistant individuals were heterozygous for cytosine (C) and tyrosine (T) nucleotides which is predicted to cause a change to the Phenylalanine (F) amino acid in the T allele. These procedures successfully identified a mutation associated with pyrethroid resistance in soybean aphid, but due to differences in resistance ratios in the MN1 and MN2 colonies compared to Sutherland, IA, there likely may be other mutations that contribute to observed resistance phenotypes.

Objective 3b. UPDATE: We furthermore predicted that the C to T mutation between putative resistant and susceptible alleles could be differentiated by digestion of a PCR product with the restriction enzyme BstEII (recognition sequence 5’-GGTNACC-3’; i.e. susceptible gDNA digested but resistant gDNA not digested). To test this, the PCR product from each individual was digested with BstEII overnight and run on a 2-3.5% agarose gel to detect differences between lab susceptible (SUS) and resistant field-collected (RES) populations. Digestion of the PCR product with BstEII yielded fragments of size 154bp and 285bp in the lab (SUS) populations. In contrast the RES populations were heterozygous and produced bands of size 154bp, 285bp (susceptible allele) and 439bp (resistant allele). These results confirmed success of the PCR-Restriction Fragment Length Polymorphism (PCR-RFLP) marker. Due to presumed dominance of the 1024F encoding resistant allele, clonal heterozygotes from the RES population would be resistant.

What it means for farmers: Preliminary evidence suggests that the kdr gene can be used a marker to more quickly identifying insecticide-resistant soybean aphids. This will speed id-work from days to hours.

View uploaded report PDF file

Updated October 1, 2019:

View uploaded report PDF file

Final Project Results

Updated October 9, 2019:
Objective 1a. Bioassays for pyrethroid resistance.
UPDATE:We collected aphids in three locations in Iowa and one in Minnesota this summer. Aphids were screened for insecticide resistance using a glass-vial bioassay treated with lambda-cyhalothrin and bifenthrin.

What it means for farmers: Insecticide resistant aphids are found in Iowa, and have been found every year since 2016. The amount of these aphids within a population is high enough to suggest that these traits are fixed and will not go away when insecticides are not used.

Objective 1b. Maintain soybean aphid colonies.
UPDATE:Four pyrethroid-resistant colonies are being maintained in our laboratory since 2018. In addition, aphids collected this summer from the same locations specified on objective 1a are being kept in mini-colonies for further studies.

What it means for farmers: The Soybean Entomology Laboratory maintains a resource that is a value to agribusiness and scientist exploring the threat of insecticide resistance in the soybean aphid. We will continue to explore these colonies to determine the mechanism and means to manage soybean aphids as pyrethroid resistance spreads. We have shared these resources with agribusiness when requested.

Objective 2a. Screening aphid susceptibility to alternative insecticides.
UPDATE:Leaf dip bioassays were performed using the soybean aphid colony most resistant to lambda-cyhalothrin and a susceptible population to lambda-cyhalothrin. The two colonies were compared for susceptibility to bifenthrin, flonicamid, flupyradifurone, sulfoxaflor, spirotetramat, and chlorpyriphos.

What it means for farmers: We have confirmed that lambda-cyhalothrin resistant aphids in Iowa. We are working to determine if these aphids are also resistant to other insecticides.

Objective 2b. Evaluating potential mechanisms for pyrethroid resistance.
UPDATE:The most resistant to lambda-cyhalothrin was used to evaluate for rapid metabolism/detoxication as a mechanism of pyrethroid resistance in soybean aphid using synergistics (Piperonyl butoxide (PBO), S,S,S-Tributyltrithiophosphate (DEF) and triphenyl phosphate (TPP)). The results obtained for the resistant population were compared to those from the lab-susceptible population.

What it means for farmers:There is the potential to manage pyrethroid-resistant soybean aphids with pyrethroids if a synergist is added. Such an addition could allow farmers to prevent outbreaks without having to switch to a different (any potentially more expensive) active ingredient. Our findings revealed that adding a synergist to a pyrethroid did not improve the efficacy when used against pyrethroid resistant soybean aphids. Because the synergist didn't work, metabolic detoxification is not a part of pyrethroid resistance in the soybean aphid. This suggests that cross-resistance is unlikely to other insecticides with different modes of action. Therefore, based on our data to date, we do not anticipate pyrethroid-resistant soybean aphids to be more resistant to insecticides like chlorpyrifos than susceptible aphids.


Objective 3a. Determine gene mutations.
UPDATE:Given the resistance to lambda-cyhalothrin identified in Objective 2, we sought to determine any genetic differences among these populations. We used a candidate gene approach to determine if previously described mutations in the voltage-gated sodium channel (VGSC), specifically, if knockdown(kdr) mutations were present in individual soybean aphids from each subpopulation. These kdr mutations change the amino acid sequence and are highly correlated with pyrethroid resistance in other insect species.

What it means for farmers: We have found evidence in the genome of the soybean aphid that a mutation is responsible for pyrethroid resistance. Such a mutation can help explain how aphids are resistant and be used as a marker to identify insecticide-resistant aphids in the field.

3b. Develop a diagnostic tool that identifies pyrethroid resistant aphids.
UPDATE:We furthermore predicted that the C to T mutation between putative resistant and susceptible alleles could be differentiated by digestion of a PCR product with the restriction enzyme BstEII (recognition sequence 5’-GGTNACC-3’; i.e. susceptible gDNA digested but resistant gDNA not digested). To test this, the PCR product from each individual was digested with BstEII overnight and run on a 2-3.5% agarose gel to detect differences between lab susceptible (SUS) and resistant field-collected (RES) populations. Digestion of the PCR product with BstEII yielded fragments of size 154bp and 285bp in the lab (SUS) populations. In contrast the RES populations were heterozygous and produced bands of size 154bp, 285bp (susceptible allele) and 439bp (resistant allele). These results confirmed success of the PCR-Restriction Fragment Length Polymorphism (PCR-RFLP) marker. Due to presumed dominance of the 1024F encoding resistant allele, clonal heterozygotes from the RES population would be resistant.

What it means for farmers: Preliminary evidence suggests that the kdr gene can be used a marker to more quickly identifying insecticide-resistant soybean aphids. This will speed id-work from days to hours.


View uploaded report PDF file

Realized Stakeholder Deliverables and Outcomes:Matt O’Neal and Erin Hodgson organized a resistance management field day in August 2017 to raise awareness of pyrethroid resistance. Outcomes from the field day:
• Understanding SBA life cycle and biology had a 1,100% percent increase.
• Knowing SBA host plant resistance options had a 900% percent increase.
• Awareness of SBA insecticide resistance had a 700% percent increase.
• Implementing integrated SBA management had a 1,000% percent increase.
• Participants were asked about their perception of value, and 100% said it was a “very valuable” workshop. There were notable behavior changes indicated in the survey summary: 58% said they will consult with ISU regarding future pest management decisions and 44% said they will scout and use economic thresholds for SBA.
• In general, respondents indicated the four speakers contributed to a successful workshop. For example, 93% of people attending the workshop said Erin Hodgson had “excellent” energy, and 100% of people said Erin had “excellent” engagement with the group and were experts in their respective fields.

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

Project Years