Effects of insecticides and synergistic chemicals on the efficacy of the entomopathogenic nematode steinernema feltiae (Rhabditida: Steinernematidae) against leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

Abstract

The Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), is considered as one of the most important pests of potato plants. Control of CPB is mainly based on chemical insecticides. However, control failure is often reported because of the rapid resistance development ability of CPB; therefore, there is an urgent need for integrated control methods. In this study, we evaluated the combined usage of insecticides chlorantraniliprole, spinosad, and spinetoram, which are registered for CPB control, with the entomopathogenic nematode Steinernema feltiae (Rhabditida: Steinernematidae).In addition, the efficacy of S. feltiae on a chlorantraniliprole-resistant CPB population exposed to synergistic chemicals PBO (Piperonyl butoxide), DEM (Diethyl maleate) and DEF (S,S,S-tributylphorotrithioate) inhibiting certain detoxification enzyme groups was determined. The tested insecticides showed no adverse effect on the survival and infectivity of S. feltiae and the isolate was considered compatible with integrated CPB control. This study also showed that pre-treatment with synergistic chemicals (particularly PBO and DEM) increased the efficacy of S. feltiae against CPB. To our knowledge, this is the first study determining the usage of entomopathogenic nematode + synergist combination. Therefore, further studies on the potential use of synergistic chemicals in combination with entomopathogenic nematodes should be performed under both laboratory and field conditions.