Scientists Investigate Processing of Bt toxin in the Gut of Armyworm Larvae

Armyworm moth (Mythimna unipuncta) is a well-known moth species due to its destructive larvae which is a pest of maize. Several studies have been conducted about the low susceptibility of the armyworm larvae to Bacillus thuringiensis toxin. Thus, a study was conducted by Meritxell Pérez-Hedo and colleagues at Universitat de Lleida, Spain to clarify if the toxin eliminated from the larvae's gut is degraded or excreted. They also observed the effects of the doses on the efficacy of the toxin.

Armyworm larvae (at 6th instar stage) were fed on with diets containing varied amounts of freeze-dried Bt or non-Bt maize leaves. Results showed that the larvae fed with varied diets had few differences in weight gain, duration of development, or pupal weight between sublethal Bt concentrations. A large part of the toxin was rapidly excreted by the larvae. Inside the peritrophic membrane, semi-permeable, non-cellular structure which surrounds the food bolus in the larvae's midgut, the toxin was eliminated, degraded, or sequestered at a rate that increase with the dose and the duration of feeding. Thus, only a small portion of the toxin reached the site of action of the toxin which is the midgut epithelium.

The findings of this study can be used to develop broader insect resistance management strategies for maize.

Read the abstract at http://onlinelibrary.wiley.com/doi/10.1111/eea.12074/abstract;jsessionid=F2FA1E32632070E1529018C9184B8227.d02t04?deniedAccessCustomisedMessage=&userIsAuthenticated=false.