Tenebrio molitor

Tenebrio molitor

The yellow mealworm beetle (Tenebrio molitor Linnaeus, 1758) is an insect belonging to the Tenebrionidae family.

Systematic –
From a systematic point of view it belongs to:
Eukaryota domain,
Kingdom Animalia,
Subkingdom Eumetazoa,
Bilateria branch,
Phylum Arthropoda,
Subphylum Tracheata,
Superclass Hexapoda,
Class Insecta,
Subclass Pterygota,
Endopterygota cohort,
Superorder Oligoneoptera,
Coleopteroidea section,
Order Coleoptera,
Suborder Polyphaga,
Infraorder Cucujiformia,
Superfamily Tenebrionoidea,
Family Tenebrionidae,
Subfamily Tenebrioninae,
Tenebrionini tribe,
Genre Tenebrio,
Species T. molitor.
The term is synonymous:
– Tenebrio laticollis Stephens, 1832.

Geographic Distribution and Habitat –
Tenebrio molitor is a beetle native to Europe, which has become cosmopolitan over time, with greater diffusion in temperate regions and the northern hemisphere; however, it is incapable of reproducing in tropical areas.
Its natural habitat in nature is that of rotting wood; in human settlements, however, it prefers mill bases, cereal drying plants, warehouses, where it feeds on flour and foodstuffs.

Morphology –
The Tenebrio molitor is a beetle with a length ranging between 15 and 20 mm, brown in colour.
This insect has a large prothorax and is equipped with membranous wings, in addition to the elytra, which allow it to fly.
The larvae are subcylindrical, bright rusty-yellow in color and with well-sclerified integument; they have short thoracic legs and measure about 30 mm in length.

Aptitude and biological cycle –
Tenebrio molitor is an insect with sexual reproduction, although cases of parthenogenesis have been reported; the eggs are laid every year in spring, but the development of the larvae is irregular, as it depends on the availability of food and environmental conditions.
Each female can produce from 275 to 600 eggs, 30-40 per day, which hatch after approximately 10-14 days.
The eggs are laid in the flour or among the residues of the kernels; the larvae feed on flour and similar foodstuffs. Their development can also last a long time, depending on nutritional and environmental conditions.
Although this insect prefers a dry environment and a temperature above 23-26 °C, it is very resistant and tolerates long periods in the cold (even three weeks at -15 °C) and without food; under normal conditions, the larva pupates after 6-7 months, without a cocoon and sometimes even moving away from the place where it grew.
The adult emerges after 7-24 days, appearing between May and September, and can reach three months of life; unlike carabids, it walks rather slowly, but it can fly and often enters homes at night because it is attracted by light.
The larvae are virtually omnivorous and develop in nature in rotting wood, while in anthropized environments they prefer cereal-based products, especially if they are about to expire. However, it also feeds on caryopsis residues, bran, remains of other vegetables and meat, tobacco, dead insects, fertilizers, feathers and bird feces, so much so that it can proliferate not only in pantries and warehouses, but also in bird nests. and bat; they have also been found in old carpets and upholstery.
It generally has one generation per year.

Ecological Role –
Tenebrio molitor is a strongly synanthropic species, which is found above all in homes, where it frequents pantries in particular; in the larval state, the flour moth is infesting and harmful, given that it develops inside foodstuffs, in particular those based on cereals such as flour, bread, pasta and biscuits; the food becomes contaminated by excrement and takes on an unpleasant taste.
This beetle lives and reproduces both in nature and in human settlements where flour, cereals, foodstuffs, etc. are present.
The damage is mainly caused by the larvae and occurs on the foodstuffs described which, contaminated by excrement, take on an unpleasant taste. We note a similar species, Tenebrio obscurus F., which behaves very similarly to Tenebrio molitor, from which it differs only in its blackish-brown livery. Finally, we remember the Tribolium castaneum, a 3-4 mm red-brown tenebrionid that infests flours and various other plant substances, which it also contaminates with a secretion with a very unpleasant odor.
To combat infestations of this insect, some precautions can be taken, both chemical and with prevention techniques.
Obviously the most suitable are prevention techniques to avoid introducing synthetic active ingredients into the environment and into foods.
In prevention, care must be taken to adopt a series of measures:
– the warehouse rooms must be perfectly impenetrable by insects. Doors and windows must have devices that allow them to be hermetically sealed. The same building must also be insulated in the foundations, to allow for any disinfestation fumigations, even under pressure; the windows must be equipped with metal or nylon nets, fine mesh, to prevent the entry of adult insects;
– in warehouses and processing rooms the following are effectively used: food traps; electric discharge light traps; sexual traps: these are particularly effective against Lepidoptera.
The use of traps can contribute to interesting results and can be conducted in various ways:
– massive capture: in this way the numerical consistency of the population is reduced by capturing males who can no longer mate;
– monitoring capture: in this way the size of the population is identified and the development cycle is followed in order to determine the intervention threshold. This allows you to identify the most favorable moment to intervene with disinfesting products and only when the size of the population is such as to cause real economic damage.
The intervention threshold varies from 1 to 2 insects per trap depending on the pest considered. If the threshold is exceeded, it is advisable to carry out a disinfestation which is carried out with fumigants or residual action insecticides; it can be done both with active infestations and with empty rooms, for preventive purposes.
Fumigations must be carried out by specialized personnel, subject to authorization from the Police Headquarters, the A.S.L., or the Port Authority.
The doses and exposure periods must be strictly respected to prevent the stored product from taking on odors which are then transmitted to the bread and other derivatives.
Furthermore, the application of doses must be rigorous to avoid the onset of resistance phenomena, also taking care to alternate the use of the active ingredients to reduce these phenomena.
Given the growing dangers in the use of insecticides and fumigants, in recent times the conservation of foodstuffs is oriented towards the use of two new technologies: controlled atmosphere and refrigeration; these new techniques which tend to replace chemical products make it possible to limit infestations and obtain products preserved without chemical residues.
These techniques involve specially constructed and naturally watertight environments.
The controlled atmosphere technique is achieved with the use of nitrogen or carbon dioxide to replace oxygen.
The best results are obtained with carbon dioxide which requires shorter application times than nitrogen, even in the presence of a certain % of oxygen.
Insects die from suffocation and from the toxic effect of CO2 at the cellular level.
The refrigeration technique allows products to be effectively preserved for long periods as the metabolism of insects is blocked.
Refrigeration times vary depending on the temperature drop chosen, which depends on the species of insects present and their stage of development.
Conservation could also be integrated, i.e. using both techniques: low temperatures associated with a controlled atmosphere.

Agri-food use –
Tenebrio molitor larvae are bred and sold (often live, but also dried or powdered) in large quantities as food for birds, reptiles, amphibians and fish, as well as fishing bait. Sometimes, breeders feed the larvae with a hormone that prevents them from transforming into adults, causing them to grow to more than 2 cm in length and 300 mg in weight.
In some regions of the world (China, Southeast Asia) they are also consumed as food by humans.
In Europe, its trade for human food use has been authorized since May 2021, following which some Italian companies are emerging that are capable of creating the first products containing dried larvae.
This is because this beetle is made up of 53% protein, 28% fat and 6% fiber and is rich in essential vitamins such as vitamin B1 which stimulates metabolic processes and improves the functions of the immune system. The amino acid content is higher than that of foods such as barley, brewer’s yeast, fish, shellfish and beef and veal.
It is also characterized by an efficient feed conversion rate, low greenhouse gas emissions, low water footprint, reduced land use and excellent ability to feed on countless types of organic waste and more.
However, in the context of the agroecological evolution of agri-food production, the energy efficiency of these methods cannot compete with that of biodiverse agroecosystems.

Guido Bissanti

Sources
– Wikipedia, the free encyclopedia.
– GBIF, the Global Biodiversity Information Facility.
– Russo G., 1976. Agricultural Entomology. Special Part. Liguori Editore, Naples.
– Pollini A., 2002. Manual of applied entomology. Edagricole, Bologna.
– Tremblay E., 1997. Applied entomology. Liguori Editore, Naples.

Photo source:
– https://www.artportalen.se/MediaLibrary/2023/5/788af7f3-623f-40ba-9c40-1f2248d4e367_image.jpg