Colorado potato beetle (Coleoptera: Chrysomelidae): Residual mortality and artificial weathering of formulated Bacillus thuringiensis subsp. tenebrionis

Potato foliage was treated with commercially formulated Bacillus thuringiensis subsp. tenebrionis Berliner and was exposed to simulated rain at different times after spray application. The treated foliage was then fed to 2nd-instar Colorado potato beetle, Leptinotarse decemlineata (Say), and larvae were held at different constant temperatures. Simulated rain applied within 30 min of the insecticide application to foliage and subsequent larval exposure to low temperature (19 degrees C) resulted in the lowest larval mortality. This was also confirmed under field conditions. The chronic effects of B. thuringiensis subsp. tenebrionis on larvae that survived initial exposure were studied. For these survivors, there was high mortality during the pupal stage and there was a delay in development to the adult stage. This mortality generally goes undetected in the field, and therefore the overall mortality caused by B. thuringiensis subsp. tenebrionis may be underestimated.