The mealworm (Tenebrio molitor) is a species of beetle insects which particularly likes cereal flour, of the order of Coleoptera, of the family of Tenebrionidae. The adult is brown-black in color (hence the name Tenebrio), the juvenile is orange-brown. The larva is vermiform, brown-yellow in color: it is called the mealworm. The adult reaches 1.5 cm on average (1.2 to 1.8 cm). At the end of its development, the larva may be longer (up to more than 2.5 cm) than adults, but narrower. It changes shape during pupation, forming a pupa.
The mealworm reproduces relatively quickly: the complete development cycle can take two to three months, if conditions are favorable (25 at 27 ° C), but can take a year in the wild. The female lays very small and transparent eggs, which are difficult to detect in the flour. Egg incubation lasts 4-18 days.
It emerges from the eggs of tiny white larvae 2 mm long, which gradually color. The number of larval stages, separated by moults, is variable: a minimum of 8, a maximum that can exceed 20. The animal is indeed capable of adapting the speed of its discontinuous development to external conditions. It will tend to grow larger and molt more if it finds food in abundance and if it lives in contact with other larvae (thus resulting in larger adults). On the contrary, it will tend to metamorphose less quickly if food resources are depleted or if it is isolated (thus giving smaller adults). The larva can reach about 30 mm in length. The larval stage lasts from 2 to 6 months depending on the temperature and sometimes even a year. Before the last moult from which the nymph will emerge, the larva no longer activates.
The pupation lasts from 6 to 20 days depending on the temperature. The transformation of the nymph into an adult is easy to observe, just watch for these few signs: the nymph is agitated with small regular movements of the abdomen; the legs, eyes and antennae turn red-brown, the ocellus (head) turns orange, the future wings and legs slowly move away from the body. Then, the nymph begins to molt, and the elytra stretch until they have their adult form.
At the imago stage, the juveniles are first almost white with a red head, then the body gradually turns reddish-brown over a dozen hours, the black coloration appears in a few days. The adult can live a few weeks (to 2 months or more) during which the female goes through several laying cycles (a few hundred eggs in total).
Prevention and recommendations
- Eliminate infected food
- Store food in airtight containers
- Use the night light in dark areas
- Maintain cleanliness in the kitchen