Weevil: [Characteristics, Detection, Effects and Treatment]

What is the weevil?

The Rhynchophorus ferrugineus, popularly known as the red weevil, is a beetle-type insect belonging to the weevils and weevils, that is, to the gigantic superfamily of the Curculionoidea, which has some 86,000 families and more than 5,000 genera. 

They are all herbivores, because they feed on vegetables and that is why they are very dangerous for the well-being of agriculture in all its forms.

How can we identify it?

These weevils have the following fundamental characteristics:

  1. Red weevils come from tropical Asia and it is one of the largest, because it reaches between 2 to 5 cm and has a very striking ferrous red color.
  2. Development of a chewing mouth apparatus that has a proboscis or proboscis shape, which can be wide and long and narrow as well, depending on the species. 
  3. It has a hard shell that protects the abdomen of the insect, which is brown in color.
  4. They have mazudo end antennae that are covered and protected by grooves that are formed along the proboscis. 

Normally, the infection in the affected palm trees is usually detected approximately one year after its infection. It is then when the danger signs become more evident and when we must apply the treatment against the red weevil to be able to save them in time. 

Some of the symptoms that affected palm trees present areː

  1. Sleeping or drooping leaves.
  2. They build galleries at the leaf insertion point, and the larvae also open meter-long galleries in the trunks of invaded plants.
  3. The cocoons of the insect are visible.
  4. In the case of palm trees, the eye is completely weakened.
  5. Some healthy leaves are seen hanging down, appearing to have been half cut.

Among the populous family of the Curculionoidea , there are other types of Weevils. Let’s see what it is.

Anthonomus grandis or cotton weevil

It is about 6 mm long and is a specialist in eating flowers and fruits of the cotton bush. From Central America he managed to travel to the United States and Mexico at the end of the 19th century.

It reproduces rapidly, is highly mobile, and has been a veritable pest of cotton crops in the southern United States. (Missouri strip).

Insecticides do not have a lethal effect on adult weevils. The female lays about 200 eggs throughout her life, wrapped in a cotton cocoon, known by the name of squares, they are like small protective capsules. 

Like other species, it is able to seal the oviposition hole with the help of its excrement, so the area is stained brown. This generates an infestation of the capsules, which end up falling off the plant , or being suspended.

Another interesting fact is that the larvae that hatch from the eggs learn to feed on the capsule tissue, in a period that goes from 7 to 14 days. After that, they pupate for about 5 more days, to give way to the young adult, who also feed on the squares or capsules and pollen.

In summary, the capsule weevil has the following life cycle: egg, larva, pupa and adult, being able to complete it in 2 to 3 weeks under ideal conditions. In large infestations, more than 50% of the harvest will surely be lost and in successive infestations the plants will not produce fruit.

But when winter arrives , many insects perish because they cannot bear such low temperatures, despite the fact that they can hibernate and keep reserves until the arrival of the hot season. The adult weevils consume cotton terminals of the seedlings without causing serious injury that retards their growth.

What plants does the weevil affect?

It lives at the expense of plants from the palm families. Coconut trees or Cocos nucifera, the so-called Oil Palm or Elaeis guineensis and others of the Phoenix genus, such as the Canary Palm and the Date Palm.

Similarly, attacks against plants of other species such as the Chamaerops humilis palm heart have been detected. And in the case of cotton plantations, the attacks are perpetrated by the cotton weevil weevil. 

How to combat the weevil?

There are several biological and chemical control methods used to combat this pest.

Cotton plant weevil weevil

A very beneficial practice is the early management of crops, in order to preserve the routes and prevent the increase of invaders, because in this way the time of vulnerability of the sowing is reduced.

If the soil temperature allows an early sowing to take place, the negative impact of the insect will be significantly reduced, since the ripening varieties, the management of the fertility of the plant and a control over the size of the plants will also be early, avoiding that they are very exuberant. 

Likewise, the application of growth regulators such as mepiquat chloride or Pix is ​​convenient. All these actions contribute to the reduction of the Weevil population.

Red weevil

In Spain, palm plantations affected by the destructive action of the red weevil have given good results with biological control methods.

In the Andalusian, Catalan and Valencian communities, various methods of extermination of the plague have been sought, achieving greater effectiveness with the introduction of parasites that feed on these weevils.

Another effective method consists of the application of a plant-type endotherapy and shower-type foliar applications, used in palm trees that do not have the apical bud cut or bitten by the larvae. The use of the fungus Beauveria bassiana89 as a biological control agent has also yielded excellent results.

What are the best products to eliminate weevils?

In the case of the square weevils that damage cotton crops, they are fought with combined actions of cultural control and chemical products.  

In general, the so-called pheromone traps are very effective, which are prepared with a synthetic or artificial version of the pheromones produced by males to attract weevils of both sexes, being able to obtain information on the type of activity and the number of adults present in the crop.

Chemical treatment

A first chemical treatment called square pinhead is done with insecticide for these weevils, which must coincide with the moment of appearance of the first squares or capsules, as soon as they begin to develop (they must be the size of a match head of phosphorus ).

This early extermination procedure avoids the appearance of an army of colonizers of weevils or square weevils, which also reduces the need to continue applying insecticide for the rest of the harvest season.

These should be combined with pheromone traps, provided the plants grow at a rate of one trap per 10-20 acres. The second method of application of insecticide is directed against populations that have exceeded the economic threshold, since they will show losses if they are not controlled.

In this treatment, about 100 squares should be randomly selected when they have already reached the size of a pencil eraser. And the insecticide application treatments each week should be repeated, until the reduction in the production of squares or capsules is seen.

Usually this is done in 4-5 day intervals, until the population is reduced. Finally, the third insecticidal treatment is an aerosol called «diapause control», it is aimed at weevils that enter the hibernation period, which must be applied after the harvest is harvested, but also before the weevils enter the wintering habitat.

It is necessary to carry out several sprays, with breaks of between 10 to 14 days. And it is suspended when the weevils perish as a result of strong frosts, or when the remains of the crop are destroyed.

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