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Lesser Mealworm

Adult Darkling Beetle
Adult Darkling Beetle
Adult Darkling Beetles
Adult Darkling beetles

Biology

Two species of beetles associated with poultry manure and litter accumulations in the Northeast are the lesser mealworm or darkling beetle, Alphitobius diaperinus, a pest of stored grain products; and the hide beetle, Dermestes maculatus, long recognized as a pest of hides,skins, and furs. Adults and larvae of both species can become extremely abundant in poultry manure and litter.

Both beetles can cause extensive damage as the mature larvae bore into structural materials, apparently seeking a safe pupation site. The lesser mealworm is also a vector (transmitter) and serves as a reservoir for several poultry disease pathogens such as acute leukosis (Marck’s disease), fowl pox, numerous pathogenic Escherichia coli serotypes, several Salmonella species, and tapeworms. Large beetle populations may become a public nuisance at cleanout time because of adult migration from the fields where the manure is spread into nearby residential areas.

Lesser Mealworm, Alphitobius diaperinus

Adult lesser mealworms are dark brown or black in color and about 1/4 inch long. The wireworm-like larvae are yellowish brown and up to 3/4 inch long. Lesser mealworms spend most of their time in the manure or litter. Adults feed on damp and moldy grain and are especially abundant in areas with spilled grain.

The life cycle is temperature dependent. There is a marked reduction in egg hatch below 70°F, and development time from egg to adult increases with decreasing temperature. Development requires 42 days at 100°F, 58 days at 80°F, and 97 days at 60°F. Eggs are laid in cracks and crevices in the manure or litter and hatch in 3 to 6 days. Most larvae develop through five to nine instars, the number increasing with lower temperatures. The last larval instar pupates in drier areas of the manure or litter and in cracks and crevices. Larvae also bore into wood posts, beams, paneling, drywall, and insulation. Small round holes about 1/4 inch in diameter are the first signs of damage. The pupal stage lasts 3 to 10 days. Adults live 3 months to a year. Generally, beetles are not observed in high numbers until manure has accumulated at least 20 to 24 weeks.

Management

Once a poultry house becomes infested, control is difficult because beetles migrate throughout the house, and pupation occurs in wood and insulation. A thorough house cleaning, combined with chemical control when the birds are removed, will usually suppress the population for a short time. Migration may be reduced by applying insecticide sprays to the pit walls and posts.

Applying dusts and sprays to manure and litter is fairly effective, but it can destroy any fly biological control agents present. Attaching well-sealed, angled, metal flashing to pit walls at the masonry-frame wall joints and to posts can help reduce immature beetle migration out of the pit; however, the rapid accumulation of dust and debris may make the flashing ineffective. Even if the flashing is effective, beetle dispersal into the community at cleanout time is a potential problem.

During spring and summer, when fly and beetle dispersal is a major concern, manure that must be removed from the building can be piled and tarped to kill developing pests. It is important that the manure be sealed completely under the tarp and the pile be placed in direct sunlight. Seal the tarp by filling 4-foot-long sections of 4-inch PVC pipe with sand, capping them, and placing them on the edges of the tarp around the base of the pile. When uncovering the manure pile, take care to avoid inhaling the excessive gas that accumulates under the tarp. Following a minimum of 2 weeks under the tarp, manure can be spread on fields without concern for pest dispersal.