The implications of introgression on the cold tolerance threshold of native Helicoverpa zea moths

In recent years, the genome of the agricultural pest Helicoverpa zea has experienced the introduction of a novel allele via introgression. While this cytochrome P450 allele, known as the B3 allele, is known to regulate the detoxification of insecticides, little is known about other potential fitness advantages it or linked genes may confer. In addition, Colorado sweet corn growers believe that H. zea are colonizing Colorado sweet corn fields earlier in the growing season than past years. The early arrival of H. zea into Colorado sweet corn fields may be the result of introgression-related changes in the overwintering ability of H. zea. To understand if introgression is impacting H. zea’s overwintering biology, we investigated the cold tolerance of admixed H. zea versus non-admixed H. zea. Through numerous temperature threshold methods, we determined that admixed H. zea can survive lower temperature thresholds compared to non-admixed pupae. Our results suggest that H. zea’s cold tolerance threshold may have changed as a result of introgression of genes from Helicoverpa armigera into H. zea and may impact their ability to overwinter in or near their historic Northward limitation in Colorado corn fields. This could explain the increase in detrimental herbivory and may lead to earlier sweet corn colonization and ultimately to larger H. zea populations. Growers will need to initiate scouting and management programs earlier in the growing season than in the recent past in order to combat increased pressure from this admixed pest.