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PBT

Student Competition 10-Minute Paper

Grad 10-min: PBT, Insecticide Resistance, Toxicology

Association of field-evolved knockdown resistance to pyrethroids in soybean aphid and frequency of resistant alleles pre- and post-foliar insecticide application

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Student Competition On-Demand
Soybean aphid, Aphis glycines (Hemiptera: Aphididae), is an invasive species in the United States, managed with foliar insecticides. However, the overreliance on the same class of insecticide has led to pyrethroid resistance in soybean aphid. We used aphids collected from a field that experienced a control failure (48.23 resistance ratio to lambda-cyhalothrin) to determine the mechanism of pyrethroid resistance. We scanned DNA and mRNA for the presence of mutations in the voltage-gated sodium channel (VGSC), which is associated with pyrethroid resistance in several insects. Comparisons of VGSC sequences from pyrethroid-susceptible and -resistant populations revealed a point mutation conferring a non-synonymous leucine to phenylalanine amino acid change (L1011F) in the resistant aphids. We developed a PCR-RFLP genetic marker to identify aphids carrying the L1011F mutation. We used this marker to assess resistance allele frequency in aphid populations collected from soybean fields both pre- and post- application of lambda-cyhalothrin at three locations in Iowa. The L1011F allele was observed in high frequency in field-collected aphids’ pre-application of an insecticide. The highest proportion of aphids carrying the L1011F mutation was observed in Kanawha, IA (100%) followed by Sutherland, IA (78%), Darwin, MN (71.19%), and Boone, IA (57.50%). The L1011F allele was 1.74-times more likely to be found post-insecticide spray. This is the first time a mutation in the VGSC has been associated with pyrethroid resistance in soybean aphid and this work could help farmers track pyrethroid resistance in real-time.