Susceptibility to eight common chemical insecticides in Helicoverpa zea populations from the southern United States

Authors: PATLA, B - Louisiana State University; SILVA, TIAGO - Louisiana State University Agcenter; LIN, S - Louisiana State University; HEAD, G - Bayer Cropscience; REAY-JONES, F.P.F. - Clemson University; Ni, Xinzhi; BERNAOLA, L - Texas A&M University; BROWN, S - University Of Tennessee; COOK, D - Mississippi State University; VILLEGAS, J - Louisiana State University Agcenter; DAVIS, J - Louisiana State University; HUANG, F - Louisiana State University

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2025
Publication Date: 12/13/2025
Citation: Patla, B., Silva, T., Lin, S., Head, G., Reay-Jones, F., Ni, X., Bernaola, L., Brown, S., Cook, D., Villegas, J., Davis, J.A., Huang, F. 2025. Susceptibility to eight common chemical insecticides in Helicoverpa zea populations from the southern United States. Crop Protection. 202:107517.

Interpretive Summary: Bollworm, also known as the corn earworm, is a highly destructive lepidopteran pest that causes severe damage on a wide range of field crops and vegetables across North America. Self-protecting or transgenic cotton and maize crops have been planted extensively for nearly three decades (since 1996) to manage corn earworm infestations in the U.S. However, the insect has recently developed widespread resistance to two bacterial proteins, leading to increased corn earworm infestations and more frequent insecticide applications in cotton to control the pest. The current study examined the susceptibility of 17 field populations of the corn earworm to eight common insecticides. The field populations were collected from six southern U.S. states in 2023 and 2024. In comparison with a laboratory reference insect colony, the field-collected corn earworm populations were still susceptible to three of the eight insecticides examined. Majority of the 17 populations exhibited low to moderate levels of resistance to some insecticides (1.4- to 31.0-fold increase), while some populations had high levels of resistance (up to >51.9 or even 141.8-fold increase). Given the uncertain future of some insecticides for agricultural use, the documented susceptibility of corn earworm to two insecticides (that is, chlorantraniliprole and Spinosad) offers options for managing corn earworm and mitigating Bt/chemical resistance in maize and cotton production the southern United States.

Technical Abstract: Larvae of Helicoverpa zea are highly destructive lepidopteran pests that damage a wide range of field crops and vegetables across North America. Transgenic Bacillus thuringiensis (Bt) cotton and maize have been employed extensively since 1996 to manage H. zea infestations in the U.S. However, the insect has recently developed widespread resistance to Cry1 and Cry2 Bt proteins, leading to increased H. zea infestations and more frequent insecticide applications in cotton to control the pest. This study investigated the susceptibility of 17 populations of H. zea collected from six southern U.S. states in 2023 and 2024 to eight common insecticides: acephate, diflubenzuron, '-cyhalothrin, spinosad, indoxacarb, methoxyfenozide, novaluron, and chlorantraniliprole. Relative to a laboratory reference insect strain, the field-collected populations were still susceptible to acephate, spinosad, and chlorantraniliprole. Most of the populations exhibited low to moderate levels of resistance to diflubenzuron (1.9-to 7.8-fold), indoxacarb (1.6- to 12.9- fold), and methoxyfenozide (1.4- to 31.0-fold), while some populations had high levels of resistance to '-cyhalothrin (up to >51.9-fold) and novaluron (up to 141.8-fold). There were no correlations in the LC50 values among the insecticides to which H. zea has developed resistance. Given the uncertain future of acephate for agricultural use, the documented susceptibility of H. zea to chlorantraniliprole and spinosad offers options for managing H. zea and mitigating Bt/chemical resistance in the southern U.S.