PALATABILITY OF FLOUR GRANULAR FORMULATIONS TO EUROPEAN CORN-BORER LARVAE (LEPIDOPTERA, PYRALIDAE)

Newly developed techniques for producing starch and flour granule formulations encapsulating Bacillus thuringiensis Berliner have led to a large number of potentially effective baits for Ostrinia nubilalis (Hubner). One aspect of these formulations that must be considered is their palatability to com borer larvae. Experiments were conducted to determine palatability of several formulations in two-choice preference tests. Com borer larvae preferred flour granules containing cotton leaves or a commercially available feeding stimulant, Coax, or both. Larvae rejected granules formulated with CaCl2. Granules made with molasses were intermediate in palatability. When the granules were formulated with 1,600 International Units (IU) B. thuringiensis per mg granules and 20 mg of granules were sprinkled on cotton leaves, several formulations killed >70% of the corn borer larvae that fed on treated leaves; other formulations killed <40% of the test insects. Mortality was reduced when larvae were exposed to cotton leaves sprinkled with granules formulated with CaCl2 when compared with those formulated with cotton leaves or Coax, or both. The dose of B. thuringiensis could be reduced by 3/4 (i.e., to 400 IU/mg) without affecting the level of larval mortality if the pathogen was entrapped in granules containing cotton leaf tissue + Coax or only cotton leaf tissue.