Field efficacy of Steinernema carpocapsae (Rhabditida: Steinernamatidae) strain All in the control of fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae) in maize

The fall armyworm, Spodoptera frugiperda (J. E. Smith) was first reported in China in 2019, causing serious damage to maize. Resistance and concealment are the main obstacles to successful use of chemical insecticides against this invasive pest. Environment-friendly and effective alternative strategies are urgently needed in China. Entomopathogenic nematodes (EPNs) have shown great potential as biocontrol agents for their ability to actively search for their host, although information on their field efficacy against S. frugiperda is limited. The present study evaluated the field efficacy of Steinernema carpocapsae (Weiser) strain All against S. frugiperda in maize fields based on bioassay of virulence toward different developmental stages of S. frugiperda. Bioassay results revealed that S. carpocapsae All caused corrected mortalities of 100 % and 62.22 +/- 1.41 % to larvae and pupae, respectively, with nematode yield ranging from 31.67 +/- 1.97 to 59.25 +/- 6.06 IJs/mg. Field experiments indi-cated that S. carpocapsae All applied at 7.5 x 108 IJs/ha into maize leaf whorls by spot-spraying achieved control efficacy (78.98 +/- 2.77 %) similarly to that by chlorantraniliprole (80.72 +/- 3.64 %). Rainfall after application significantly accelerated and enhanced the control efficacy achieved by S. carpocapsae All. Nine days after application, 39.99-53.64 % and 18.27-22.37 % of the initial nematode population was detected in plants and soil, respectively, which indicated marked persistence of the EPNs with the control efficacy <= 41.75 +/- 5.59 % against larvae or pupae. Our findings indicate that S. carpocapsae All has marked potential for achieving the safe biocontrol of S. frugiperda in maize.