Wheat Weevil, The ‘pantry Plague’
Weevils constitute a group of beetles of the Curculionidae family . Within this group, there are different subgroups. The wheat weevil subgroup belongs to the Sitophilus genus .
General characteristics of the wheat weevil
The wheat weevil is a subgroup belonging to the order Coleoptera and the family Curculionida . All specimens of the three species range in size between 2 and 4 millimeters.
A peculiarity of this group is its elongated snout, which adapts to the size of the grain. The three species in this subgroup are dark brown, although each has some character of its own.
Infestations occur both in the importation of grains or cereals, in the plantations or in the stores that store the food, or in the transport vehicles themselves.
Depending on the species, they can be found in some places or in others.
Females deposit a single egg inside the grain and seal it with a mucilaginous secretion. The larval stage and pupal period occur within the grain. However, when the wheat weevil is developed, it leaves the cocoon.
When the wheat weevil needs to get out of the grain, it makes a big hole. This hole is one of the signs that confirm its presence.
Sitophilus granarius or wheat weevil
This beetle is dark brown, almost black, with a bright touch. Its hue is lighter than that of the other two species. Furthermore, it lacks blemishes on the body.
Although its body is elongated and cylindrical, it does not exceed 4 millimeters, nor is it less than 2 millimeters. Another feature is that this species does not have wings, like others in its family.
Although the wheat weevil does not fly, its infestations occur both in the import of grain and cereals and in the stores that store the crops, or in the transport vehicles themselves: it does not feed on the grain planted in the field.
Wheat weevil breeding conditions are very specific. They require a temperature between 13 °C and 35 °C. On the other hand, another condition is that the grain has a moisture content of 9.5%.
Habitat and distribution
Wheat weevils can be found in different types of climates, with changes in temperature.
It was observed that adults and young specimens are resistant to low temperature climates. Not all species in this subgroup tolerate the cold.
Consequences of the presence of the wheat weevil
Wheat weevils are primary pests. This implies that they not only attack the grains, but also infect other products made from them. For example, the noodles.
Grains infected with wheat weevil are easily recognized due to the large holes caused by the exit of adult specimens. These grains are not marketable, which has an important economic impact.
Sitophilus oryzae or rice weevil
Adults of this species have a dark brown body with bulges. It has yellowish spots and its length varies between 2.5 and 4 millimeters.
Externally, it is not possible to differentiate the species Sitophilus oryzae and Sitophilus zeamais. The only way to tell them apart is to do a dissection of Organs genitals.
This species also has ideal conditions to develop. They require temperatures between 15 ºC and 34 ºC, as well as relative humidity values above 40%.
Sitophilus zaemais or corn weevil
The corn weevil belongs to the wheat weevil subgroup and is the smallest of the three. The Sitophilus zaemais is distributed in tropical and subtropical regions.
Sometimes, when they are in food already stored, they can be transported to temperate zones. This species feeds on corn in the plantation itself.
Damage from beetles
If the expansion of any one of these species is not controlled, the repercussions can be extremely important. Currently, there are different plans for dealing with these species, including a good storage system.
The damage they do is characteristic, and is none other than the hole made by the insect to get out of the grain. In addition, they also feed on the grain itself. This generates moisture and heat in the grain, which attracts other types of insects and fungi.
The consequence in the economic sphere is important, since these pests reduce the quality of the grain and, therefore, its commercialization. Above all, its eradication is difficult.