The Red Palm Weevil (Rhynchophorus ferrugineus) is a reddish-brown beetle about 3.5cm long, originally coming from Southeast Asia. This little pest is a Coleopteran snout beetle, with a slightly comical snout and elbowed antennae, and will feed on a broad range of palms including coconut, sago, date, and oil palms.

It was ‘deported’ to Spain and the Canary Islands in exported plants and can be found now in other Mediterranean countries, and is thought to have entered Portugal on imported palms, potentially threatening other palm trees in the region. It has been found in North Africa, the Middle East, the Med and parts of the Caribbean and Central America, and constitutes a severe agricultural problem by apparently wiping out many palm farms.

You may have seen palm trees stricken down, with leaves fallen or falling, leaving a very unattractive trunk, which eventually has to be removed completely. As some of these palms have been standing proud in their locations for some years, why doesn’t someone do something about getting rid of the evil weevil that causes the damage? Some owners, on finding out the palm is infected, chop it down and dump it, where unfortunately the beetles just jump ship to another tree and chomp their way into that one as well.

The Red Palm Weevil (RPW) has various and numerous host plants. Here in Portugal, it is primarily palms, and among these especially the Phoenix canariensis, a feather palm that can reach up to 15m, and constitutes an important part of Portugal's scenery. Although it has no harvestable crop to speak of, this handsome tree is the most visible and significant palm in our local landscape and has been extensively planted, especially in the Algarve - in parks, hotels, villa developments and private gardens, giving a tropical feel to the environment. Portugal would look very different without its most common palms and apparently there is every indication we might lose these exotics, in addition to other more unusual members of the family if serious, national and community-wide measures are not taken.

The concealed feeding habit of RPW borer is the main reason why spraying environmentally harmful chemical insecticides is not controlling the pest. Systematic insecticides can be injected directly into palm trunks, and applying systematic insecticides to the soil helps to eliminate the weevils in the egg stage, but must be repeated two or three times every year. Natural predators would seem to be the best option, with over 50 natural enemies reported to attack them, with fungi being the most promising ones for biological control.

Detection

Detecting the weevil threat in the first place (at larvae stage) is difficult, as when a palm tree shows visible signs of distress, it generally means that the infestation is well-advanced, and at this point, it is too late to rescue the tree. The first detectable signals of an infested tree originate from the noise produced by the weevil larvae while consuming the core of a trunk. Until now, the early detection techniques of RPW rely mainly on visual inspection and pheromone trapping. Several methods to detect RPW infestation have recently emerged, and these include remote sensing, highly sensitive microphones, thermal sensors, drones, acoustic sensors, and sniffer dogs.

The problem is still relatively new to Portugal but it is just another stage in a process that began in the 1980s when the beetle started to spread. Moreover, this new arrival in the Algarve is only a small part of a much larger picture, the naturalist E.O. Wilson recognised long ago as a major challenge of our age - the invasion of exotic species. Portugal has certainly not been exempted.

As well as the common Agave and sugarcane, over 30 palm species including both of Europe’s two native palms are on the RPW menu, with the insect being particularly fond of date palms and, for reasons which remain a mystery, it is especially drawn to males of the Canary Island Date. In neighbouring Andalucia in Spain, it is said that in the first eight months of 2008 alone, over 10,000 palm trees had been destroyed because of the weevil. This should warn us about what Portugal can expect.

Author

Marilyn writes regularly for The Portugal News, and has lived in the Algarve for some years. A dog-lover, she has lived in Ireland, UK, Bermuda and the Isle of Man. 

Marilyn Sheridan