Compatibility of Steinernema carpocapsae and Steinernema feltiae with cypermethrin against the beet armyworm Spodoptera exigua

The beet armyworm, Spodoptera exigua, is one of the most important polyphagous ubiquitous pests of the sugar beet. Because of adverse effects of conventional pesticides, introduction of new safe control methods in beet army worm management is essential. The aim of this study was evaluating compatibility of two EPN species, Steinernema carpocapsae and S. feltiae with cypermethrin against beet army worm larvae. Contact and oral toxicity of EPNs and cypermethrin was evaluated against six days old beet armyworm larvae. The recorded LC50 values of S. carpocapsae and S. feltiae were 6.63 and 4.41 IJ/Larvae, respectively. This value for cypermethrin was 465.4 ppm. Combination effects were tested at three concentrations of EPNs including 2, 4, and 6 IJs/Larvae and 160 and 320 ppm of cypermethrin. Nevertheless, the negative effect of cypermethrin on EPNs, synergistic effects on larvae mortality were recorded at combination treatments 160 ppm Cyp+2 IJs/Larvae EPNs, similar effect was also recorded at treatment contained 320 ppm cypermethrin and same level of IJs of S. feltiae. Larvae mortality was enhanced by increasing the exposure time to cypermethrin and also in combination with EPNs. This increasing trend was also recorded for 48 hours of post-exposure to EPNs and then the curve became plateau.