The lesser mealworm beetle, Alphitobius diaperinus is a smaller beetle measuring about ¼ inch to 1/6 inch (4 to 6mm) long. It is a dark reddish-brown color with strong ridges on the wing covers. The upper corners of the prothorax behind the head are acutely rounded and the sides are nearly straight and parallel. These characteristics cause the prothorax to appear to be almost rectangular in shape. The lesser mealworm beetle can be confused with a close relative – the black fungus beetle, Alphitobius laevigatus. The key difference is seen in the eyes. When viewed from the side, the eyes of the lesser mealworm beetle are almost divided in two by the margin of the head. This division is less severe in the eyes of the black fungus beetle.
This beetle is a common pest in poultry houses and can appear in quite large numbers in the litter of the floor of such facilities. The beetle harbor and transmit disease organisms to chickens and turkeys and can be an annoyance to poultry farm workers. Lesser mealworm beetles are strong fliers and can migrate to neighbouring properties. They will also be observed in grain storage facilities in pockets of out-of-condition grain and grain products and in spills of grain. Lesser mealworm beetles also have been found infesting cereals, chocolate, cocoa and tobacco. Home infestations are not common except when beetles are migrating from nearby barns, silos, etc.
Eggs are laid by female beetles in the soil or directly into the litter in poultry houses. The larvae that hatch are active crawlers and if population densities grow too large, both larvae and adults will bore into walls and insulation and move higher into the building, It is from these locations that infestations of fresh litter occurs. Larvae also tunnel into walls and insulation to pupate, as well as into soil. The life cycle typically is completed in 35 to 60 days.
In poultry houses, the lesser mealworm beetle will be found in the loose litter and in tunnels bored into walls and insulation. Use a knife or a thin spatula to force beetles hiding in cracks into the open.
When infestations of yellow or dark mealworm beetles are found, removal of all infested food product should be completed. Treatments of cracks in those areas with a residual insecticide may be needed in case adults or larvae are harboring there.
Controlling lesser mealworm beetles in poultry houses requires a plan of regular sanitation and treatments with residual insecticides. When the chickens or turkeys are removed from a broiler house, the building is usually scheduled for cleaning. All old litter must be removed and the floor thoroughly washed. A general treatment with an appropriately labeled residual insecticide can then be made to the floors and walls of the building.