The efficacy of entomopathogenic nematodes plus an adjuvant against Helicoverpa zea and Chrysodeixis includens in aboveground applications

Authors: Zhang, Minling; Spaulding, Nathan; Reddy, Gadi V.P.; Shapiro Ilan, David

Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2024
Publication Date: 5/8/2024
Citation: Zhang, M., Spaulding, N.R., Reddy, G.V., Shapiro Ilan, D.I. 2024. The efficacy of entomopathogenic nematodes plus an adjuvant against Helicoverpa zea and Chrysodeixis includens in aboveground applications. Journal of Nematology. 56/1-14. https://doi.org/10.2478/jofnem-2024-0018.
DOI: https://doi.org/10.2478/jofnem-2024-0018

Interpretive Summary: The soybean and corn earworm are major pests of row crops. The insects are generally controlled with chemical insecticides. However, due to environmental and regulatory concerns, alternatives to chemical insecticides are needed. Entomopathogenic nematodes, also known as beneficial nematodes, are safe environmentally friendly alternatives to chemical insecticides. Ten strains of entomopathogenic nematodes were tested against eggs, larvae, and pupae of corn earworm and soybean looper in the laboratory. Then, the best two strains of entomopathogenic nematodes were chosen for efficacy testing in the field with an adjuvant 0.066% Southern Ag Surfactant. In field experiments, the adjuvant Southern Ag Surfactant treatment significantly increased the mortality and entomopathogenic nematodes infection for entomopathogenic nematodes strain Steinernema carpocapsae (All) on 1st instars of corn earworm in corn plant whorls. On soybean plants, with the adjuvant Southern Ag Surfactant, entomopathogenic nematode strain S. carpocapsae (All) was more effective than the strain S. riobrave (7-12) on the 5th instars of soybean looper. This study indicates that entomopathogenic nematodes can control against corn earworm and soybean looper and that Southern Ag Surfactant adjuvant can enhance entomopathogenic nematode efficacy.

Technical Abstract: Ten strains of entomopathogenic nematodes (EPNs) were tested for virulence against eggs, 1st to 4th instars, 5th instars, and pupae of corn earworm (Helicoverpa zea) and soybean looper (Chrysodeixis includens) in the laboratory. These ten EPN strains were Heterorhabditis bacteriophora (HP88 and VS strains), H. floridensis (K22 strain), H. georgiana (Kesha strain), Steinernema carpocapsae (All and Cxrd strains), S. feltiae (SN strain), S. rarum (17c+e strain), and S. riobrave (355 and 7-12 strains). The EPN dose was 1 mL at a rate of 100 IJs/mL per Petri dish per ten eggs or one larva/pupa. EPNs could infect the eggs of H. zea or C. includens in the laboratory, but the infection rates were low. The mortalities caused by ten EPN strains in 7 days were significantly higher for the 1st-4th instars of H. zea compared to the control, and so did the 5th instars of H. zea. Similarly, for the 1st-4th and 5th instars of C. includens, the mortalities were significantly higher compared to the controls, respectively. However, only S. riobrave (355) had significantly higher mortality than the control for the pupae of H. zea. For the pupae of C. includens, except for H. bacteriophora (HP88), S. rarum (17c+e), and H. floridensis (K22), the mortalities of the other seven strains were significantly higher than the control. Subsequently, S. carpocapsae (All) and S. riobrave (7-12) were chosen for efficacy testing in the field with an adjuvant 0.066% Southern Ag Surfactant (SAg Surfactant). In field experiments, the adjuvant SAg Surfactant treatment significantly increased the mortality and EPN infection for S. carpocapsae (All) on 1st instars of H. zea in corn plant whorls. On soybean plants, with the adjuvant SAg Surfactant, S. carpocapsae (All) was more effective than S. riobrave (7-12) on the 5th instars of C. includens. This study indicates that EPNs can control against H. zea and C. includens, and that Southern Ag Surfactant adjuvant can enhance EPN efficacy.