The red palm weevil, Rhynchophorus ferrugineus, is a beetle of Asian origin. In recent years, it has made headlines due to its numerous damages to palm trees and, consequently, to public greenery. The fight against this parasite is necessary, as well as obligatory, to prevent the disappearance of palm trees. Thanks to studies and experiments, today it is possible to eliminate the red palm weevil without the use of chemical pesticides. Precise monitoring of its presence and appropriate treatments allowed in organic farming can, in fact, at least partially solve the problem.
In this article, we will start with the visual recognition of the red palm weevil, show monitoring and prevention strategies, and understand which treatments are most effective in combating this dangerous parasite.
Identification of the Red Palm Weevil
Rhynchophorus ferrugineus is an insect belonging to the order Coleoptera, superfamily Curculionoidea. It is known as the red palm weevil (in English, red palm beetle) due to its striking and unmistakable appearance.
This parasitic insect originates from South Asia and made its first appearance in Europe in Spain in 1994. In Italy, it has been present since 2005, gradually spreading to all regions where palm trees are found.
Description of the Red Palm Weevil
The red palm weevil is easily recognizable in its adult form:
- It measures between 19 and 45 mm in length and 11.50 to 15.50 mm in width.
- It has a long, curved rostrum, more pronounced in males, from which brownish hairs protrude, and its antennae are inserted.
- It has six strong legs.
- Its color ranges from red to rust, with small black spots on the thorax.
- It has striated elytra (wings) that are darker in color than the rest of its body.
The eggs are whitish-yellow, oval in shape, measuring from 2.5 to 3.9 mm, and they give rise to larvae. These larvae are legless, up to 50 mm long, with a brownish sclerified head.
Pupae, the intermediate stage between larvae and adults, are initially white, then turn brown. They measure from 35 to 50 mm and are protected inside a puparium. This puparium is constructed by the larvae using plant fibers. It is a true nest, tight and covered with a waterproof layer. The pupal cocoon of the red palm weevil is oval and elongated, measuring up to 80 mm in length and about 35 mm in width.
The Life Cycle of the Red Palm Weevil
The red palm weevil completes its entire biological cycle inside the palm tree.
Adults can live up to 6 months and can fly up to 1 km away. This is one reason for the ease of geographic spread of this beetle. Females lay an average of 200 eggs but can lay up to 700. Oviposition occurs in cavities in the trunk or in areas where leaves are usually cut. Due to the palm’s morphological structure, it is easy for the insect to find recesses in which to reproduce. Once mature, the insect feeds on the host plant for a few days before migrating and reproducing on another plant. The life cycle is continuous, lasting about 3-4 months in total, and multiple overlapping generations of red palm weevils can be found in more favorable environments, with up to four generations per year. It’s important to note that the red palm weevil has a huge reproductive potential.
In less than a week, the eggs hatch into larvae that begin to penetrate the tree’s tissues and feed on them.
With their trophic activity, red palm weevil larvae create deep galleries, moving from one part of the plant to another. The cavities they create are ideal for the insect’s development. The larvae can be found in all parts of the plant, but they generally prefer the vegetative apex. Their development takes between 1 and 3 months, depending on the season. Growth is faster in warmer weather. Once mature, the red palm weevil larva pupates and creates a cocoon using palm fibers, called the “pupal chamber.” This cocoon is easier to find on the outer part of the trunk. From this moment, it takes about a month for the red palm weevil to complete its cycle and become an adult.
Which Plants Does the Red Palm Weevil Affect?
Like the Asian stink bug or the Japanese beetle, the red palm weevil causes severe damage as an “alien” species to our ecosystem, and therefore, it is not naturally counteracted by antagonistic insects. This parasite is essentially harmful to plants belonging to the botanical family Arecaceae, namely palm trees. The most significant damage has been recorded in the following species:
- Phoenix canariensis, Canary Island date palm;
- Phoenix dactylifera, date palm;
- Chamaerops humilis, Mediterranean fan palm;
- Brahea armata, Mexican blue palm;
- Butia capitata, jelly palm;
- Washingtonia, Mexican fan palm.
What Damage Does the Red Palm Weevil Cause to Palm Trees?
The damage to palm trees caused by the red palm weevil is due to the trophic activity of the larvae and is often asymptomatic. This means that until the infestation is in an advanced stage, it is difficult to detect the presence of the parasite. The first visible damage is seen on the central leaves typical of palms: there are deformities, truncations at the apex, and incisions on the margins. It is easier, unfortunately, to recognize palm trees attacked by the red palm weevil in an advanced stage. The typical symptom is the abnormal shedding of young leaves. These detach at the base, with the peculiarity that the older leaves remain relatively healthier and greener. As the infestation progresses, the entire vegetative apex is destroyed, resulting in the collapse of the canopy, which loses its symmetry and takes on the so-called “open umbrella” shape. When the infestation reaches this stage, the palm tree is compromised and no longer recoverable. In fact, red palm weevil adults migrate, seeking other plants to destroy after completing their work. Approaching the trunk of a palm tree attacked by the red palm weevil, you can hear the noise of the larvae excavating the galleries. Another peculiarity of the damage is the foul odor emitted by the palm. This is due to the erosion of internal plant tissues, causing foul-smelling decay and putrefaction.
How to Prevent the Red Palm Weevil
Agronomic prevention to avoid red palm weevil infestations is difficult to implement. As mentioned earlier, damage is often noticed in advanced stages when it is already too late to intervene. However, there are some common-sense rules, a sort of prophylaxis to follow to be able to intervene promptly. Here’s what they are:
- Periodic and thorough inspection of palm trees in your garden. This operation, in public areas, must be performed by green maintenance professionals;
- Caring for the plant through regular pruning, including the removal of dead leaves and exhausted leaf sheaths. This is a way to determine if you are dealing with normal palm leaf shedding or an ongoing red palm weevil attack;
- Avoiding cutting green leaves for purely aesthetic purposes, as it makes the plant more vulnerable to the red palm weevil;
- Disinfecting wounds from pruning cuts to prevent easy entry for the insect.
The best way to determine the presence of the red palm weevil is by using pheromone traps. These are special traps developed in recent years that use a sexual attraction pheromone specific to Rhynchophorus ferrugineus, commonly called Ferrugineol. These traps are useful for establishing the presence of the red palm weevil in a given area. Unfortunately, individual traps are insufficient for mass capture, as many traps would need to be placed, making this defense very costly. Moreover, the traps should not be placed under the palm tree, as is done, for example, in the fight against the olive fly, but at least 30 meters away from the palm tree to prevent the red palm weevil from being attracted to the palms.
How to Eliminate the Red Palm Weevil
The elimination of the red palm weevil is subject to community and national legislation. The fight against this dangerous parasite is made mandatory by the following measures:
- Decision 2007/365/CE “Emergency measures to prevent the introduction and spread of R. ferrugineus in the Community”;
- DM 07/02/2011 “Provisions for mandatory control of the red palm weevil R. ferrugineus”.
At the regional level, there are also various regulations aimed at containing Rhynchophorus ferrugineus.
Anyone, whether a public or private entity, with palm trees that are inevitably compromised by the red palm weevil, must proceed with the felling and removal of the plant. This is the safest method to prevent the spread of the insect.
In advanced stages of infestation, unfortunately, there is no possibility of saving the plants.
How to Dispose of Red Palm Weevil-Infested Plants
The destruction of palm trees affected by the red palm weevil is not simple and must be carried out by specialized companies. The problems are due to the large size of the plants and the disposal of the remains. The authorized methods for disposing of residues are:
However, only chipping/shredding ensures 100% elimination of the parasite, provided it is carried out within 24 hours of felling. This way, the beetle will not have time to move elsewhere. Specialized companies cut the palm into large pieces, which are wrapped in plastic bags and disposed of at designated sites. It is needless to say that these operations are very expensive.
Insecticides Against the Red Palm Weevil
Chemical control of the red palm weevil is authorized by the Ministry of Health, using registered synthetic insecticides.
Chemical treatments are of two types:
We do not advocate for these defense methods because, at Coltivazione Biologica, we are against the use of chemical pesticides, regardless of the circumstances.
There are methods allowed in organic farming that are effective in controlling early-stage red palm weevil infestations.
We are talking about entomopathogenic nematodes, especially those belonging to the Steinernema carpocapsae strain, which we have already discussed when talking about the black vine weevil.
The authorized and registered product by the Ministry of Health is called NemoPAK SC Palme. The treatment with this product is carried out by direct spraying on the apical bud. In essence, the product is poured onto the central shoot and the side leaves of the palm tree. In the case of plants infested at an early stage, the treatment should be repeated three times at weekly intervals. As a preventive measure, that is, on uninfested palm trees, the action of entomopathogenic nematodes can be used more frequently, with 6 treatments carried out during the summer and autumn seasons. Another useful biological product as a remedy for the red palm weevil is azadirachtin, the active ingredient in the neem tree. This biological product can be used in conjunction with entomopathogenic nematodes and enhances the effectiveness of the treatment.