Assessment of toxicity and persistent of Yersinia entomophaga and its Yen-Tc associate toxin.

BACKGROUND The insect-pathogenic bacterium Yersinia entomophaga MH96 is currently under development as a microbial pesticide active against various pasture and crop pests such as the diamondback moth Plutella xylostella and the cotton bollworm Helicoverpa armigeria. To enable non restricted field trials of Y. entomophaga MH96, information on the persistence and non-target effects of the bacterium and its Yen-Tc proteinaceous toxin are required. RESULTS The Y. entomophaga Yen-Tc associated toxin was found to have limited persistence on foliage and is inactivated by UV light. The Yen-Tc was rapidly degraded in ovine or bovine rumen fluid or the intestinal fluid of H. armigera. In H. armigera an intestinal protein of greater than 50 kDa was found to cleave the Yen-Tc. Assessment of Y. entomophaga persistence on foliage and in soil found that after 42 days the bacterium could not be detected in soil at 20% soil moisture content but persisted 72 days at 30-40% soil moisture. Non-target effects of Y. entomophaga towards earthworms found the bacterium afforded no adverse effects on worm growth or behavior. A summary of historic Yen-Tc and Y. entomophaga persistence and toxicity data is presented. CONCLUSION The bacterium Y. entomophaga and its Yen-Tc associated toxin have limited persistence in the environment, with the Yen-Tc being susceptible to UV inactivation and proteolytic degradation, and the bacterium persisting longer in soil of a high moisture content. This article is protected by copyright. All rights reserved.