Dark mealworm
Tenebrio obscurus Fabricius

Order: Coleoptera
Family: Tenebrionidae
Acronym: TOB

Ecology

The dark mealworm is found worldwide. In Canada, it is reported from British Columbia, Alberta, Ontario, Quebec and Newfoundland. It is a minor pest of stored grain and milled products. It prefers decaying grain residues and damp milled products which have been undisturbed for some time. It feeds on both animal and plant materials like flour, bran, meal, grains, insect remains, meat and feathers. The dark mealworm is often found along with the yellow mealworm (Tenebrio molitor) infestations. In Canada, the dark mealworm is reported infesting poultry houses, stables, mills, feed plants and warehouses.

Damage

The dark mealworm is a generalist feeder. Its damage is not distinctive. Both the adult and larva feed on the commodity. It is a minor pest of cereals and cereal products, especially if grain is damp or in poor condition. Their presence in stored grain indicates poor storage conditions. Signs of infestation are a disagreeable odour in the commodity.

Life history

The adult is a dull, reddish-brown to black beetle. It is parallel-sided and slightly flattened. It is one of the largest stored product pest insects, 12 – 18 mm long. It is most similar in appearance to the yellow mealworm. The dark mealworm has more dense punctures on the face, head and thorax than the yellow mealworm. The dark mealworm’s body colour is also dull rather than glossy like the yellow mealworm. The adult is long-lived and can survive from 2 weeks to 3 months. There are reports of dark mealworms surviving up to 2 years. Adults can fly.

The dark mealworm female lays between 400 – 500 eggs. She lays her eggs singly or in clusters within the commodity.

The larva is cylindrical. It is active and moves through the commodity. Young larvae are white and turn dark yellow to brown as they mature. It has two short urogomphi located at the tip of the last abdominal segment. A fully grown larva may be 25 – 30 mm long. Optimal conditions for development are a temperature of 24°Cto 27°C and a relative humidity of 70%. Development time may take from 4 months to 3 years. The larva is cold resistant. The larva will feed on other insects if they are present.

Control

Controlling insect infestations

Images

Clemson Univ./USDA CES, Bugwood.org
Dark mealworm - Larva