Lack of Efficacy of In Vivo- and Putatively In Vitro-Produced Bacillus popilliae Against Field Populations of Japanese Beetle (Coleoptera: Scarabaeidae) Grubs in Kentucky

Abstract

Use of Bacillus popilliae Dutky, causal agent of milky disease in Japanese beetle grubs, has been limited because of its inability to produce infective spores in vitro. Recently, putative milky disease products produced by a patented in vitro process were marketed. We evaluated in vivo- and putatively in vitro-produced commercial spore formulations for efficacy against Japanese beetle grubs in laboratory and field trials. In soil confinement assays, infectivity by feeding (per os) was greater for the traditional spore powder made by maceration of diseased grubs than for the putative in vitro formulation. However, in multi-year field trials on 2 golf courses, neither product was effective in inducing higher levels of milky disease or in reducing grub populations. Application of a full dose (2 g) of spore powder, the amount normally applied every 1.2 m in a grid pattern, within 0.1-m 2 field enclosures failed to induce milky disease in grub populations in soil directly beneath the treated turf. Laboratory-infected 3rd instars in late phases of milky disease continued to feed on grass roots. Putatively in vitro-produced formulations were recalled from the market in 1991 because of questions about the identity of the bacterial spores they contained. We challenge the evidence that commercially available spore powder, applied according to conventional methods, is effective for suppressing localized grub populations in turfgrass, and suggest that standard recommended practices for use of milky disease bacteria should be reevaluated.