Enhanced toxicity of Bacillus thuringiensis japonensis strain Buibui toxin to oriental beetle and northern masked chafer (Coleoptera: Scarabaeidae) larvae with Bacillus sp. NFD2

Abstract

Bacillus thuringiensis japonensis strain Buibui (Btj) has the potential to be an important control agent for pest scarabs. Bioassays using autoclaved and nonautoclaved soil showed there were always lower LC50 values associated with nonautoclaved soil. We identified five other bacteria found in the hemolymph of insects killed by Btj and used them in bioassays to see whether we could enhance the control achieved with Btj alone. One bacterium, designated NFD2 and later identified as a Bacillus sp., showed the greatest enhancement of Btj in preliminary experiments and was used in bioassays with Btj versus oriental beetle, Anomala orientalis (Waterhouse), and northern masked chafer, Cyclocephala borealis Arrow (Coleoptera: Scarabaeidae), larvae. This bacterium alone was nontoxic to grubs in bioassays. A combination of this bacterium with Btj in nonautoclaved soil resulted in a significantly lower LC50 value (0.23 g toxin per g soil) from all other treatments for A. orientalis with one exception; the LC50 where NFD2 was added back into autoclaved soil (0.29 g toxin per g soil). A combination of this bacterium with Btj in nonautoclaved soil resulted in a significantly lower LC50 value (48.29 g toxin per g soil) from all other treatments for C. borealis with the exception of the treatment where Bacillus sp. NFD2 was added back to autoclaved soil (96.87 g toxin per g soil) with Btj. This research shows that other soil bacteria can be used to enhance the toxicity of Btj and possibly other Bts. © 2010 Entomological Society of America.