The pea weevil (Bruchus pisorum Linnaeus, 1758) is a beetle belonging to the Chrysomelidae family.
From a systematic point of view it belongs to:
Species B. pisorum.
The terms are synonyms:
– Bruchus pisi Linnaeus, 1767;
– Dermestes pisorum Linnaeus, 1758;
– Laria pisorum (Linnaeus).
Geographic Distribution and Habitat –
Bruchus pisorum is a beetle found in Europe and northern Asia, North America, temperate Asia and South Australia but with other small presences in South America and South Africa.
The natural range of this insect is Asia Minor, wherever its host plant is present, which is mainly the pea.
Its ability to survive in dry pea seed for an extended time has led to its being transported to other regions rather than through natural migration, so much so that it is now considered cosmopolitan.
Indeed, this insect is a big problem in peas in most of southern Russia. Additionally, a survey has found this beetle in southeastern Europe and the Middle East, including Bulgaria, Yugoslavia, Albania, Greece, Turkey, Syria, Lebanon, Israel, Iran, and Afghanistan. Its presence has also been reported in Japan and parts of China. It is also found in South America and has been described as the major pest of peas in Chile. Also, by the early 1930s, B. pisorum had become established in several areas of southwestern Australia.
The Bruchus pisorum is a small beetle, with a length of about 4 mm.
It has blackish elytra with small whitish spots, which leave the pygidium partially uncovered.
The head is short and strongly narrowed behind the eyes. The antennae extend less than a third of the length of the body. The pea weevil also has a well-defined denticle on the lateral margin of the pronotum.
The larva, with the typical “C” shape, is white in color with a brown head and short legs.
The eggs are bright yellow-orange and are laid singly on the pods.
Attitude and biological cycle –
The Bruchus pisorum overwinters in the adult stage inside the attached seeds or in shelters. In spring, the adults emerge from the seeds and begin their nutritional activity; they immediately mate to reproduce.
Females usually lay on the surface of the pods and the eggs usually hatch in three to five weeks, depending on the temperature.
The young larvae penetrate directly through the pod wall from the underside of the egg. Once inside the pod, they look for a soft developing seed.
This beetle has four distinct larval stages. Larval development ranges from seven to 11 weeks and the pupa from two to three weeks. Adults emerge during the summer from the seeds of unharvested crops and fly to overwintering sites or remain in the harvested seeds until the following spring or until disturbed.
In this way this insect completes only one generation per year.
Ecological Role –
The Bruchus pisorum is an insect that in the adult stage feeds on pollen and nectar, without causing major damage to crops. After mating the female lays her eggs on the surface of the pea pods. The phytophagous larvae penetrate the pod and feed on the seed tissues, developing inside them. The infested seeds are no longer edible or usable as seeds.
The larvae, on the other hand, are phytophagous and live by feeding on pea seed tissues. The damage occurs on the pea seeds and is caused by the trophic action of the larvae. These, generally one per seed, empty the pea seeds making them unmarketable both for food use and as seed; in fact the seeds lose their ability to germinate or, if they germinate, they give rise to very weak plants with stunted growth.
The arrival of the weevil is a crop that often coincides with the beginning of flowering, but if there are no flowers they take refuge in the vegetative parts of the crop.
To avoid the infestations of this beetle, it is necessary to adopt prevention and fight techniques.
First of all, we need to start from the possibility of making the pea storage warehouses perfectly impenetrable by insects. Doors and windows must have devices that allow them to be hermetically sealed. The same building must also be isolated in the foundations, to allow for any disinfestation fumigation, even under pressure; the windows must be fitted with metal or fine-meshed nylon nets to prevent the entry of adult insects.
Furthermore, food traps, electric shock light traps and sex traps can be used in warehouses and processing rooms.
The traps can be used for both mass trapping and monitoring.
– massive trapping is useful for decreasing the numerical consistency of the population, by catching males who can no longer mate;
– monitoring capture, on the other hand, serves to establish the size of the population and thus determine the intervention threshold. This makes it possible to identify the most propitious moment to intervene with pesticides 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 pest considered.
If disinfestation is therefore necessary, this has been carried out up to now with fumigants or insecticides with a residual action; it can be done both with infestations in progress and with empty premises, for preventive purposes.
The fumigations must be carried out by specialized personnel, subject to authorization from the competent bodies, taking care, however, to verify the doses and exposure periods which must be strictly respected to prevent the stored product from taking on odors which are then also transmitted to the bread and other derivatives .
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.
In recent times, the conservation of foodstuffs has been orienting itself towards the use of two new technologies: controlled atmosphere and refrigeration; these new techniques that tend to replace chemical products make it possible to limit infestations and to obtain products preserved without chemical residues and, above all, to not introduce residues harmful to flora, fauna and people into the environment.
Obviously these techniques require specially constructed and of course airtight environments.
The controlled atmosphere technique is carried out with the use of nitrogen or carbon dioxide instead of 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.
In these conditions the insects die from suffocation and from the toxic effect of CO2 at the cellular level.
The refrigeration technique makes it possible to effectively preserve the products for long periods as the metabolism of the insects is blocked.
The refrigeration times vary according to the chosen drop in temperature, which depends on the species of insects present and their stage of development.
An integrated technique can also be adopted by exploiting the two methods, namely the use of low temperatures together with a controlled atmosphere.
– Wikipedia, the free encyclopedia.
– GBIF, the Global Biodiversity Information Facility.
– Russo G., 1976. Agricultural entomology. Special Part. Liguori Publisher, Naples.
– Pollini A., 2002. Handbook of applied entomology. Edagricole, Bologna.
– Tremblay E., 1997. Applied entomology. Liguori Publisher, Naples.