Efficacy of the newly discovered entomopathogenic nematode Steinernema adamsi against Helicoverpa zea: life stage susceptibility, UV tolerance, and field performance

Authors: Glover, James; Spaulding, Nathan; George, Justin; Portilla, Maribel; Reddy, Gadi; DILLMAN, ADLER - University Of California, Riverside

Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2025
Publication Date: 4/23/2025
Citation: Glover, J.P., Spaulding, N.R., George, J., Portilla, M., Reddy, G.V., Dillman, A. 2025. Efficacy of the newly discovered entomopathogenic nematode Steinernema adamsi against Helicoverpa zea: life stage susceptibility, UV tolerance, and field performance. Journal of Nematology. 57:1-11. https://doi.org/10.2478/jofnem-2025-0012.
DOI: https://doi.org/10.2478/jofnem-2025-0012

Interpretive Summary: Helicoverpa zea is a significant pest affecting cotton and other row crops, causing economic damage and developing resistance to chemical insecticides. This study explored the potential of the entomopathogenic nematode Steinernema adamsi and its mutualistic bacteria Xenorhabdus as biological control agents for managing cotton bollworms. Laboratory experiments showed that S. adamsi was effective in killing early instar larvae, but older larvae were more resistant to EPN infection. The nematode’s sensitivity to UV light was also evident, with longer UV exposure significantly reducing its effectiveness. In addition, the bacterial symbiont Xenorhabdus proved highly virulent when directly injected into larvae, causing 100% mortality. However, when ingested by the larvae, the bacteria were less effective, resulting in only 36% mortality. Field trials demonstrated that combining S. adamsi with protective agents like sodium alginate (which prevents desiccation) and Congo red (a UV protectant) dramatically increased larval mortality, with up to 98% effectiveness. This suggests that formulating nematodes with protective additives can improve their performance under harsh field conditions, making them a promising alternative to chemical pesticides for managing H. zea. Further research is needed to optimize nematode formulations and application strategies to ensure efficacious results in agricultural environments.

Technical Abstract: Helicoverpa zea is a major agricultural pest, particularly in cotton, and poses significant challenges due to its ability to develop resistance to chemical insecticides. This study evaluates the efficacy of the entomopathogenic nematode (Steinernema adamsi) and its mutualistic bacteria (Xenorhabdus) as biological control agents against H. zea larvae in both laboratory and field settings. In laboratory assays, mortality rates for 1st to 4th instars were high, ranging from 74.2% to 100%, while 5th instars exhibited significantly lower susceptibility (<37% mortality). Pupae were utterly resistant to nematode infection. The impact of UV radiation on nematode efficacy was assessed, with mortality decreasing from 100% in control conditions (0 hours UV exposure) to 71.8% after 5 hours of UV exposure, highlighting the vulnerability of S. adamsi to UV degradation. In addition, Xenorhabdus caused 100% mortality in H. zea larvae when injected directly into the hemocoel, but oral toxicity was significantly lower, with 36% mortality in 7 days post-exposure. Field experiments demonstrated that the combination of S. adamsi with 0.05% sodium alginate (hygroscopic agent) and 0.02% Congo red (UV protectant) resulted in a significant increase in larval mortality. In field test A, where S. adamsi was applied in water, mortality averaged 56% with 82% EPN infection. In field test B, the combined treatment of sodium alginate and Congo red led to 98% larval mortality, although infection rates were lower and statistically non-significant. The addition of these protective agents likely enhanced the environmental stability and efficacy of the nematodes under field conditions. These findings suggest that S. adamsi can be an effective biological control agent for H. zea, particularly when combined with formulations that protect against UV radiation and desiccation. Future research should focus on optimizing nematode delivery systems to improve field efficacy under diverse environmental conditions.