Yellow mealworm
Tenebrio molitor L.

Order: Coleoptera
Family: Tenebrionidae
Acronym: TMO

Ecology

The yellow mealworm, largest of the insect species that attack stored grain and grain products, can be found in storages across Canada. It prefers damp areas and old grain that has remained for more than a year in remote corners of the storage areas. Its presence is an indication of poor sanitation. The larvae are reared commercially as fish bait and as pet food for amphibians, fish, reptiles and mammals. They are also used by entomologists in evaluating pesticides.

Damage

These insects are scavengers. They prefer damp, decaying grain or milled cereal products, and will also feed on meat scraps and dead insects.

Life history

The adult of this species is a shiny, dark brown to black beetle about 15 mm long. Under unheated conditions there is usually only one generation annually, although the life cycle may be extended to 2 years. The adults appear in early summer and the females soon deposit their eggs, either singly or in small clusters, in the food material or on the sides of the bins. Each female lays about 300 to 500 sticky, white eggs. When hatched, the young larvae are white but soon turn a characteristic yellow and grow to a length of 30 mm. The larvae are resistant to dryness and cold, with a demonstrated ability to survive for 3 weeks at temperatures as low as -15°C.

Control

Sanitation and moisture are very important factors in the control of the yellow mealworm. This involves a thorough cleaning of all storage areas to remove old grain, followed by the use of an approved structural insecticide. Also ensure that wall and floor cracks are repaired and that basement areas are kept as dry as possible.

Images

Drawing of an adult yellow mealworm

Yellow mealworm in pupal stage.

Larva of a yellow mealworm.

Adult yellow mealworm.