The ténébrion miller ( Tenebrio molitor ) is an insect coleopter able to live in very dry stored food products, in particular in the flour, from where its name of miller. The adult is of color brown-black (from where the word Tenebrio ) and the larva is vermiform, of color chestnut-yellow: one calls this larva the worm of flour ( yellow mealworm in English). The adult reaches 1,5 cm on average (1,2 to 1,8 cm). At the end of its development, the larva can be longer (until exceeding 2,5 cm), but less broad than the adult. It changes form during the metamorphosis, by forming a Nymphe.

It is a cosmopolitan insect, probably of origin European, but disseminated with the four corners of the world for a long time, because of the commercial exchanges of foodstuffs of which it is fond of delicacies.

Breeding

One can find this insect in the majority of the animaleries because it is high for various uses: fishing, food of the birds or the reptiles and, even, sometimes, for the human consumption (Entomophagie, to see low).

This insect is inoffensive. The breeding in is very easy, with the range of the children, and it is completely recommended to the schools for observations on the development of the insects. It is enough to buy some larvae in a animalery and to put them in a container of plastic or metal containing of the flour (on one or two cm in height). It is necessary that container has walls smooth (to prevent that the insect climbs) and to avoid the paperboard or wood (which would be corroded). The larvae are inserted in the flour to nourish itself and go back to driven surface to carry out their and them metamorphosis. One can also give them sound, bread, croquettes for cat, or any other dried food product.

A remarkable characteristic of this animal is that it is not necessary to give him water, which simplifies the breeding largely of it. Indeed, it is able to recover the water contained in the atmospheric air and very desiccated food. As much of others Tenebrionidae, it is adapted to living under desert conditions.

However, this insect can be regarded as omnivore (polyphagous), because it also affectionate the fruits or vegetables. In breeding, a piece of apple or carrot, from time to time, or some peelings washed in order to remove them from any insecticide, will make it possible the larvae more quickly to take weight. In addition, this animal does not hesitate to devour its congeneric when they died, wounded or simply weakened by the moults of metamorphosis. So that the breeding perdure, it is thus advised to isolate the young lately formed nymphs (which do not need to eat) and to give them in a vat of food only 2 or 3 days after the adult moult.

In breeding, the ténébrion adult remainder in the vat of flour and it does not fly. It however has wings and the live animals in nature make use of it sometimes. It is not at all easy to recognize a male of a female when they are adult (the brown or black color is not at all a valid criterion). The difference is easily visible only with the level of the nymph which makes it possible to observe the genital parts in formation at the end of the abdomen.

From the facility of its breeding, this insect also was very much used in the research laboratories for physiological studies on its development and its endocrinology: its nymph is very sensitive to the youthful Hormone for example, which in particular made it possible to study this hormone in detail, like much of mimetic compounds (modulating endocriniens) or Pesticide S.

Reproduction and development

The ténébrion reproduces relatively quickly: the complete development cycle is carried out into two to three months, if the conditions are favorable (25 to 27 °C), but can take one year in nature. The female lays eggs very small and transparent, difficult to detect in the flour. It leaves there tiny white larvae, which color themselves little by little. As in all the arthropods, the growth is discontinuous: the animal is covered with a rigid Cuticule, being used to him as Exosquelette, which it must renew periodically to manufacture some larger. It is the phenomenon of the driven .

The number of larval stages, separated by moults, is variable: a minimum of 8, a maximum which can exceed 20. The animal is indeed able to adapt the speed of sound discontinuous development to the external conditions. It will tend to grow bigger more and to make more larval moults, if it finds food in abundance and if it lives in contact with other larvae (thus giving larger adults). On the contrary, it will tend to be metamorphosed less quickly if the food resources become exhausted or if it is insulated (thus giving smaller adults).

The life of the Nymphe is from 6 to 20 days according to the temperature and the adult can live a few weeks (less than 2 months) during which the female carries out several cycles of laying (a few hundreds of eggs on the whole).

Entomophagie

This insect is often used by the followers of the Entomophagie and is put in the high-speed motorboat by television programs showing of the constrained competitors to eat some to make a success of a test. It is necessary however to be certain quality of the breeding or to avoid the raw consumption of this insect because it can be vector of Ver S parasites connected with the Ténia (of the kind Hymenolepis ).

Others Tenebrionidés

Two other kinds of Ténébrionidés are comparable with Tenebrio for several their biological characteristics, but different primarily by their size:

• the kind Zophobas includes/understands insects much larger, the larvae reaching up to 5 cm. These species, probably of South American origin, are often called morios in the animaleries (the most sold species is Zophobas morio ) and are also described as ténébrions giant . Their larger size makes it possible to feed from very large birds or reptiles. A remarkable characteristic of these insects is that they do not carry out their metamorphosis that if they are insulated: the breeding groups the constrained one to remain permanent larvae, which moult from time to time, but without entering in nymphose.

• the kind Tribolium is on the contrary much smaller (a few mm only in an adult state). It thus does not interest the animaleries for the fishing or the breeding of birds and reptiles. But Tribolium castaneum is a model of invaluable study for the geneticists because it has, like the Drosophile, a very short development cycle and many identified mutants. Its genome is in way to be completely sequence.

External bonds

• Card of Insectarium of Montreal

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