Abstract
Survival rates of the infective juvenile stage (IJ) of two entomopathogenic nematodes (EPN), Steinernema carpocapsae and Steinernema sp. isolate K8 (Thai isolate), plus a surfactant of 0.2% and 0.4% APSA-80™, a fire retardant gel of 0.25% and 0.5% Barricade®, and tap water were investigated by spraying the EPN suspensions (200 IJs) onto kale leaf discs. Three hours after incubation, the survival rates of the EPNs plus 0.25% and 0.5% Barricade® (80.2–85.0%) were significantly higher than all other treatments (12.9–70.1%). The infectivity of the two EPNs plus 0.25% and 0.5% Barricade® against third-instar Spodoptera litura F. and Plutella xylostella L., which were evaluated by spraying 100 IJs/50 μl onto a 1 cm kale leaf disc in the laboratory, were 82.5–100% 72 h after application. In greenhouse tests, the infectivity of S. carpocapsae plus 0.25% and 0.5% Barricade® against third-instar S. litura and P. xylostella was evaluated by spaying 2500 IJs/15 ml/plant and assessing mortality after 72 h. The results showed that the mortality rates of S. litura larvae in the S. carpocapsae plus 0.25% or 0.5% Barricade® treatment (66.0% and 61.5%, respectively) were significantly higher than in the S. carpocapsae plus tap water treatment (29.5%) and also resulted in significantly less leaf damage (11.0–11.1%) compared to control treatments (33.8–61.6%). A significant difference between the mortality rates of P. xylostella larvae (15.0–27.0%) and the percentages of leaf damage (7.1–11.0%) were also recorded for the same two treatments. Overall results were similar to previous studies which showed that fire retardant gel (Barricade®) can improve EPN virulence when they are applied to control these two insect pests. Barricade® could protect EPNs from rapid desiccation for at least 3 h following application.