Biology

Invasive species (III): The red palm weevil, the scourge of palm trees

“Red palm weevil” is the common name of Rhynchophorus ferrugineus , an insect of the order Coleoptera and belonging to the Curculionidae family, better known as weevils or weevils (due to the elongated shape of their alimentary apparatus). It is a native Asian species, with a striking rusty iron color and can reach five centimeters in its adult phase, which is a relatively large size for a beetle, although it does not normally exceed 2 cm in length.

The red palm weevil feeds on different species of palm trees, such as the coconut or the date palm. It is an invasive species in several countries in Africa, America or Europe, including Spain. This species was detected for the first time in our country in Granada, in 1993 , coming from Egypt or from another country in North Africa. It then spread throughout the southeast of the peninsula, then moving north (where its development is more difficult due to the climate and the scarcity of palm trees to feed on) and also reached the Canary Islands.

In the archipelago, the Canary Island palm or Canary Island palm, Phoenix canariensis, an endemic species of the islands , was affected Its distribution limit in the northwest of the peninsula is the province of Pontevedra, where measures are being taken to prevent it from continuing to advance.

Red palm weevil life cycle

Red weevil larvae develop inside the trunk of palm trees, burrowing galleries as they grow. They are capable of almost completely emptying the trunk of the plants, causing the highest specimens to fall, with the consequent danger in parks and public roads with palm trees.

The larvae live for about 100 days inside the trunk; Once developed, they form a cocoon on the outside with fibers from the plant itself and within this envelope they metamorphose. Adult beetles also feed on plants and their ability to fly allows them to colonize new palm trees and spread.

They are capable of flying long distances and each female lays hundreds of eggs. Due to this, the growth of the pest is rapid from the time it is introduced in a locality until it moves through the surroundings.

Adults detect kairomonas, chemicals secreted by palm trees in the air when they have an injury or due to pruning of their leaves, and this helps them find new specimens to feed and lay their eggs.

Pest control

There is an action protocol against red weevil infestations that is effective in many cases. In the Canary Islands, where the insect is considered eradicated, more than 700,000 palm trees were inspected over ten years, of which 200,000 received a treatment against the red palm weevil and only 700 were felled.

[box type = »info» align = »» class = »» width = »»] Cutting down palm trees affected by red weevil should be the last measure to be taken, when the previous ones have been shown to be ineffective. In addition, the trunk must be buried several meters deep to ensure that the adults do not complete their life cycle and leave the dead palm in search of others. All this makes the felling process expensive and cumbersome, resulting in more effective control of the pest through the use of phytosanitary products. [/ Box]

The use of a fungus for biological control of the red weevil is also being studied . It is Beauveria bassiana , an ascomycete fungus that parasitizes different insects, causing them to die. Applied in a controlled way, it is effective in the control of numerous pests, since it does not have harmful effects on human beings nor does it affect pollinating species.

This fungus is being used against the red palm weevil in the Palm Grove of Elche, declared a World Heritage Site and which has more than 200,000 specimens of palm trees, most of the species Phoenix dactylifera , commonly called the date palm.

Future perspectives

red palm weevil
red palm weevil

In the case of the biological invasion of the red palm weevil in Spain, the prospects are not at all dramatic. There are effective methods to control the pest and it has already been eradicated from part of the affected territory (the Canary Islands).

However, it is important not to skimp on efforts to eradicate it from the rest of the Iberian Peninsula as well, and special attention should be paid to those areas where the red weevil is not yet present but may be present in the future. Correct action in the early stages of a biological invasion is important to minimize the negative effects of this and to reduce the cost of fighting the pest.

In the case of the red weevil, a recommendation to take into account is to paralyze the pruning of the palm trees if adults of the beetle are detected in the area , since the open wounds on the trunk of the plants act as a source of propagation of this species.

The symptoms of the presence of the red weevil are the appearance of galleries in the area where the leaves join the trunk, the presence of cocoons formed by plant fibers at the base of the trunk and apparently healthy leaves appear hanging.

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