Agricultural entomology: Pea weevil

Agricultural entomology: Pea weevil

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Classification and host plants

Class: Insects
Order: Beetles
Suborder: Polyphages
Family: Bruchidi
Genus: Bruchus
Species: B. pisorum L.

Bibliographic reference:
Phytopathology, agricultural entomology and applied biology” – M.Ferrari, E.Marcon, A.Menta; School edagricole - RCS Libri spa

Host plants: Pea (seed).

Identification and damage

The Tonchio del Pisello is a small beetle (about 4 mm long). The body, which is blackish and covered with hair, also has diffuse light gray spots on the elytra; these leave the pygium uncovered which is clearer. The adult is pollinofago and glicifago and therefore does not directly cause any damage. The larva, which has an arched body, is white with a brown head; it has very short bristles and is equipped with short legs. The larvae are phytophagous and live feeding on the tissues of the pea seed. The damage occurs on the pea seeds and are caused by the trophic action of the larvae. These, generally one per seed, empty the pea seeds making them incommerce both for food use and as seeds; in fact, the seeds lose their germination or, if they germinate, they give rise to very weak plants with slow growth.

Biological cycle

The Tonchio del Pisello spends the winter in the adult stage inside the seeds attached or in shelters.
In the spring, the adults come out of the seeds and begin their nutritional activity; they immediately mate to reproduce. Females generally lay on the surface of the pods. The newborn larvae pierce the pod and then enter the seed to dig it internally. The larvae, having reached maturity, pupate in the seed which has now reached maturity. The adult insect does not come out of the seed but overwinters inside; it will come out, as already said, in the following spring. The Tonchio del Pisello performs one generation a year.

Pea weevil adult - Bruchus pisorum L. (photo

Pea weevil - Bruchus pisorum L. (photo


Prevention and fight techniques
Prevention and control techniques must follow the following basic rules:
- the rooms intended for the warehouse must be perfectly impervious to insects. Doors and windows must have measures that allow their hermetic closure. The same building must also be isolated in the foundations, to allow any disinfection fumigation, even under pressure; the windows must be equipped with metal or nylon nets, with fine mesh, to prevent the entry of adult insects;
- in warehouses and processing rooms they find effective application: food traps; electric discharge light traps; sexual traps: these are particularly effective against Lepidoptera.
With these traps you can get different results:
- massive capture: in this way the numerical consistency of the population is reduced, by capturing the males who can no longer carry out mating;
- 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 to identify the most propitious moment to intervene with pest control products and only when the size of the population is such as to cause real economic damage.
The threshold varies from 1 to 2 insects per trap depending on the phytophagous considered;
disinfestation is carried out with fumigants or with residual action insecticides; it can be done both with current infestations and with empty rooms, for preventive purposes.

The fumigation must be carried out by specialized personnel, with the authorization of the Police Headquarters, the A.S.L., or the Harbor Master's Office.
The doses and the periods of exposure must be strictly respected to prevent the stored product from taking on odors which are then also transmitted to bread and other derivatives.

Residual insecticides (contact action)
The application of the doses must be rigorous to avoid the onset of resistance phenomena, it is also advisable to alternate the use of the active ingredients, to reduce these phenomena.

Other conservation methods
Preservation of food is currently focusing on the use of two new technologies: controlled atmosphere and refrigeration; these new techniques that tend to replace chemicals allow to limit infestations and to obtain products preserved without chemical residues.
These techniques provide specially built and naturally watertight environments.
The controlled atmosphere technique is carried out with the use of nitrogen or carbon dioxide to replace oxygen.
The best results are obtained with carbon dioxide which requires shorter application times, compared to nitrogen, even in the presence of a certain% of oxygen.
Insects die from suffocation and the toxic effect of CO2 at the cellular level.
The refrigeration technique allows you to effectively store products for long periods as insect metabolism is blocked.
Refrigeration times vary according to the chosen temperature drop, 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.

Video: Pulse School: Taking a closer look at pea leaf weevil pressure (May 2022).