They attack only members of the white grub family. Milky Spore disease affects some 47 different varieties of beetle grubs in the U.S. including June Beetle or May Fly grubs, but the Japanese beetle grub is probably the most extensively affected. Milky disease bacteria do not infect nor harm other insects, earthworms, birds, warm-blooded animals, humans, or plants. The spores germinate inside the grubs, and multiply rapidly in their blood. When the bacteria become very numerous in the blood they again form spores, completing the bacterial cycle.
Some diseases kill insects in a few hours or days, but the milky disease works slowly.
Infected grubs may live for months after their blood has become loaded with spores, particularly if temperatures are low. Sometimes, grubs that become infected late in fall will live until spring. Since moles and voles primarily feed on beetle grubs, milky disease will virtually eliminate these varmints from your lawn by removing their food. Adult Beetle Populations Applications of spore powder to lawns and parks are most effective in reducing adult beetle populations when it is done on a community basis. When all land in a community is thoroughly inoculated with milky-disease bacteria, it usually is not possible for large numbers of grubs to survive and transform into adults.