Milky disease

Pathogen and disease type. Bacillus lentimorbus is a gram-positive, spore-forming bacterium classified as an entomopathogen. It is not a plant pathogen but a biological control agent that causes the well-known milky disease in the larvae of scarab beetles. By targeting the larval stage of specific soil-dwelling insects, this bacterium functions as a natural mechanism for regulating pest populations in agricultural ecosystems.

Targeted pests and impact. The primary hosts for this bacterium are the grubs (larvae) of various beetles, including the European chafer and the Japanese beetle. These larvae feed on the roots of a wide array of crops, including turfgrass, corn, cereals, and many vegetable crops. By inducing disease in these larvae, Bacillus lentimorbus indirectly protects the root systems of agricultural plants, preventing the significant economic losses associated with root destruction.

Symptoms and signs. The disease is aptly named because of the distinct physical change in the host's hemolymph. Once the bacteria enter the larval gut and penetrate the body cavity, they reproduce rapidly, causing septicemia. As the bacterial population explodes, the hemolymph transforms into a thick, milky-white fluid that is highly visible through the insect's cuticle. Infected larvae become sluggish, cease feeding, and eventually perish.

Development and spread conditions. The disease flourishes in environments where soil moisture and temperature are favorable for bacterial growth. After a host dies, the carcass eventually decomposes, releasing millions of viable spores back into the soil, which creates a reservoir for future infections. The spread is primarily facilitated by the movement of grubs through the soil, as they come into contact with contaminated areas and ingest the bacterial spores.

Protection and prevention measures. Implementing Bacillus lentimorbus as a biological control strategy is a cornerstone of integrated pest management in many regions. To maintain the efficacy of this natural defense:

• avoid excessive use of broad-spectrum soil chemicals that may disrupt natural biological balance;
• promote soil health to ensure the viability of spore reservoirs;
• apply bio-insecticides containing the bacteria to areas with high grub infestations to establish long-term population suppression.