Lesser mealworm

Lesser mealworm Alphitobius diaperinus adult stage

General

The darkling beetle, or lesser mealworm, Alphitobius diaperinus is one of the most abundant insects found on the floor of poultry houses. It has long been known as a common pest worldwide, and while its origins are unclear, it was likely carried out of Sub-Saharan Africa and dispersed via global trade routes. The beetles feed on spilled feed and chicken waste and are eaten by the chickens in turn, posing a risk for disease transmission, especially Salmonella. These insects reproduce quickly and are difficult to control. They hide in wall cracks and other tight spaces, evading routine cleaning and disinfection procedures.

Life cycle and appearance of Lesser mealworm

The adult darkling beetle lays hundreds of eggs over the course of its life in cracks and crevices, manure, litter, and under feed and water lines. The eggs are oblong, about 1.5 mm (0.06 inches) in length and creamy white at first but darken over time. Larvae hatch four to seven days after the eggs are laid and complete their development over six to eleven larval instars in 40 to 100 days, depending on temperature and food availability. They are slender, segmented, worm-like insects with three tiny pairs of legs near the head. Final instar larvae disperse to pupate in secure, isolated locations.

The pupae superficially resemble shorter, stubbier larvae and change colour from creamy white to tan-brown, just before the adult emerges in five to ten days. Lesser mealworm adults are shiny, black beetles with a slightly-flattened oval shape. They are about 6 mm (0.25 inches) long and they have parallel rows of tiny depressions running lengthwise along their wing covers (elytra). Both larvae and adults are primarily nocturnal and most active at dusk. Adults can live more than a year (up to two in ideal conditions).

Damage symptoms

Lesser mealworms congregate in large numbers around feed and water stations and breed prolifically, with the following consequences:

The birds eat them and can develop lesions in their digestive tract due to damage caused by the beetles’ hard wing covers.
They can carry and transmit many different pathogens including:
- bacteria (Salmonella, Escherichia, Bacillus, Streptococcus species and avian tuberculosis);
- fungi (Aspergillus);
- viruses (Marek's disease, Newcastle disease, fowlpox, avian leucosis and infectious bursitis a.k.a. Gumboro disease); and
- avian coccidiosis.
They damage the poultry housing when final instar larvae tunnel into thermal insulation to pupate and when the adult beetle further enlarges the existing tunnel when it emerges.