Milky spore

Paenibacillus popilliae (formerly Bacillus popilliae) is a soil-dwelling, Gram-positive, rod-shaped bacterium. It is responsible for a disease (commonly called milky spore) of the white grubs of Japanese beetles.

The adult Japanese beetles pupate in July (in the Northeast United States) and feed on flowers and leaves of shrubs and garden plants. During this adult stage the beetles also mate and the females lay eggs in the soil in late July – early August. The eggs hatch soon afterwards and in this larval or grub stage, they feed on the roots of grass and other plants. As the weather gets cooler and winter approaches the grubs go deeper in the soil and feeding declines as they over-winter.