HortFACT
Identification
The adult beetle is dark brown, elongate, moderately convex, somewhat shining, and from 17 mm to 25 mm long. Males and females have well developed wings and superficially look alike. They prefer dark, humid, and dingy places inside warehouses, mills, or grain stores.
The egg is oval, opaque, milky white and shining, about 1.5 mm long by about 0.60 mm wide. A female lays 250-1000 eggs singly or in small clusters on the food. When first laid the eggs are covered with a sticky secretion, and particles of food quickly coat them.
The newly hatched larva is white but becomes yellowish brown as it grows in length from 2mm to 25mm or more. Fully grown larvae closely resemble wireworms in appearance. The number of larval stages [instars] varies from 9 to 21.
When ready to pupate, larvae move to the surface of the infested food and spend a few days as prepupae before becoming pupae. The pupa is about 15 mm long, 5 mm broad, white when first formed but soon changing to yellowish brown, and has a row of characteristic lateral lamellae on each side. It has no cocoon or protective covering.
Host plants
Yellow mealworm is not a field pest, but infests stored products such as flour, meal and other cereal products. It is easily reared, and is frequently used as food for caged birds and reptiles.
Damage
Yellow mealworm is primarily a pest of flour and meal, but also infests grains, cereals, and other mill products, particularly in dark, moist places where the grain has not been disturbed for some time. Both larvae and adults feed on these products, growing and breeding rather slowly. They do less damage than many other smaller beetles. Yellow mealworm has been found in (but does not feed on) salt, soda ash, and black pepper, and may also feed on meat scraps, feathers, and dead insects.
Distribution
Yellow mealworm is cosmopolitan [distributed throughout the world].
Life cycle
| Egg |  |
| Larvae | |
| Pupae | |
| Adult | |
| Month | |
| Note: Coloured bars indicate periods of peak activity in each of the life cycle stages | |
The eggs hatch after 4-18 days; the larval stage usually lasts 6-9 months. The mealworms usually overwinter in the larval stage. The pupal period ranges from 6 to 18 days, and adults usually live 2-3 months. The length of the life cycle of yellow mealworm depends on the food and the environment. Under favourable conditions the shortest period from egg to adult stage is about 120 days, but under less favourable conditions a period of 629 days (about 2 years) has been recorded. In the laboratory at 25oC the complete life cycle takes about six months.
PRITAM SINGH