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.

www.isaaa.org