Which biological insecticide is ineffective against Japanese beetles in Iowa?

Bacillus popillae is recognized as ineffective against Japanese beetles in Iowa because it specifically targets the larvae of the Japanese beetle, rather than the adult beetles. While Bacillus popillae can be beneficial in managing grub populations in the soil, its efficacy does not extend to controlling the adult form of the Japanese beetle, which is what poses significant damage to plants.

In contrast, other biological insecticides may have broader applications or effectiveness against various pest stages. Bacillus thuringiensis is known for its activity against caterpillars, while Bacillus cereus and Bacillus subtilis have different modes of action or target other pests. Understanding the specific life stages and types of pests each biological insecticide targets is crucial for effective pest management.