Failure of entomopathogens to control white grubs (Coleoptera: Scarabaeidae)

Abstract

White grubs are the root-feeding larvae of scarab beetles (Coleoptera: Scarabaeidae), and they are among the most destructive pests of turfgrass, pastures and horticultural plants in many parts of the world. A two-year field experiment was conducted to control different white grub species in an organically utilised meadow with dry forage conservation. The efficacy of Beauveria brongniartii, Beauveria bassiana, Bacillus thuringiensis var. kurstaki, B. thuringiensis var. tenebrionis and Heterorhabditis bacteriophora was tested against the white grubs in comparison with untreated control (only water suspension was used). The application of biological control agents was conducted twice (April and August). Our observations show that several biological control agents are capable of controlling the populations of the first and second instar larvae of different scarab grub species. The efficacy of most biological control agents, however, declines when larvae reach the third instar stage. The most promising combination tested in our study is that of entomopathogenic fungi and H. bacteriophora for controlling the first- and second-stage instar larvae. In addition, the summer application proved to be more suitable for control of the first-stage instar larvae than the spring application.