Unfortunately Malta has been hit by the devastating Red Palm Weevil. We have been noticing an alarming number of Phoenix canariensis which have been infected by this destructive weevil. Unfortunately one notices the presence when its already too late in the day to save these trees.
Information on Red Palm Weevil was first published in 1891 in India. This pest was first described as a serious pest of the coconut palm in 1906, while in 1917 it was described as a serious pest in the date palm in the Punjab, India.
In 1918, Red Palm Weevil caused serious damage to the date palm in Mesopotamia (Iraq) but no insect specimens were collected to confirm it.
Red Palm Weevil entered and was discovered during the mid-1980s in the Arabian Gulf countries. However, it has become a most destructive pest of date palms in the Middle East.
The cause of the high rate of spread of this pest is human intervention, by transporting infested young or adult date palm trees and offshoots from contaminated to uninfected areas.
The red palm weevil is a member of Coleoptera: Curculionidae. The male and female adults are large reddish brown beetles about 3 cm long and with a characteristic long curved rostrum; with strong wings, they are capable of undertaking long flights.
Damage to palms is produced mainly by the larvae. Adult females lay about 200 eggs at the base of young leaves or in wounds to the leaves and trunks; the grubs feed on the soft fibers and terminal bud tissues. They reach a size of more than 5 cm before pupation. Except just before pupating, they move towards the interior of the palm making tunnels and large cavities. They can be found in any place within the palm, even in the very base of the trunk where the roots emerge.
Pupation occurs generally outside the trunk, at the base of the palms. The larva pupates in a cocoon made of brown dried palm fibres.
Overlapping generations with all life stages can be present within the same palm tree. Generally the adult weevils present in a palm will not move to another one while they can feed on it.
Usually the damage caused by the larvae is visible only long after infection, and by the time the first symptoms of the attack appear, they are so serious that they generally result in the death of the tree. This late detection of the presence of the weevil constitutes a serious problem in the fight against the pest and in any attempt to guarantee pest-free status in adult trees. Despite research carried out so far, no safe techniques for early detection of the pest have been devised.
In Spain, very soon after the red palm weevil killed the first Phoenix canariensis in some gardens of Almuñecar, the relevant authorities initiated various actions to combat the pest.
Intensive chemical treatments have been used to protect the Phoenix palms and to try to cure affected trees. Despite the difficulty in operating in the public gardens environment, foliage spraying has been conducted with various insecticides: Fenitrotion, Clorpirifos, Diazinon or Metidation. Preventive treatment of all the palms, even healthy ones, has been repeated once a month outside the tourist season.
Insecticides such as carbaril and imidacloprid have been injected several times and in various places all around the stems of palms. Simultaneously, a programme of mass trapping using aggregation pheromone and semi-synthetic kairomone has been initiated (Esteban-Durán et al. 1998). But despite all these efforts, more than one thousand Phoenix have been killed. In an area that extends from Motril to Nerja, in the Mediterranean coast of Granada and Málaga, the weevil is still present and has spread to villages close to the initial points of infection.
There is every evidence to suggest that the first weevils were introduced into Spain from adult palms imported from Egypt. Before the arrival of the weevil in the south of Spain, Egypt was the westernmost place where the red palm weevil has been recorded. Furthermore, as the importation of palms from Egypt was not prohibited, Egypt has been the main source of supply of ornamental adult Phoenix palms to satisfy the very substantial demand that exists in all the coastal cities of Spain and, more generally, of southern Europe.
In Egypt itself, the introduction of the red palm weevil was caused by an importation of offshoots from the United Arab Emirates. At the beginning, the extension of this pest into Egypt was restricted to a limited number of locations in two northeastern provinces. In 1995, three years after its first discovery in Egypt, an Egyptian agriculture official considered that the red palm weevil had been eradicated (Ferry 1996). Unfortunately, this announcement was erroneous. In the two provinces where the pest was first recorded, the red palm weevil continues to infect and kill new date palms year after year, despite all the efforts developed to combat it.
Various techniques have been used to try to control the red palm weevil (pheromone traps) and to save infested date palms (chemical control by pouring pesticides into the trunk and injection of entomopathogenic nematodes (Shamseldean 1994)). Despite good results of these techniques in the laboratory, they are not efficient enough in the field to succeed in eliminating red palm weevil. The reason for this is probably the great difficulty in reaching all life stages of the weevil inside an adult palm tree, even with intensive and repeated stem injections or perfusions. Furthermore, such intensive activity is impossible for economic and practical reasons in places with a large number of date palms.
In Egypt, as well as in the south of Spain, the elimination of infested trees has not been applied systematically as soon as the pest were detected. The possibility of saving these trees and avoiding serious economic consequences as a result of their elimination, and the practical difficulties of carrying out this operation have unfortunately limited or delayed the destruction of infested trees. The affected trees have then constituted an important focus for further spread of the red palm weevil.
At present the situation in Egypt is very worrying. Although a small number of date palms are affected, red palm weevils have been recorded in each of the Delta administrative districts, as well as in some orchards along the road between Cairo and Alexandria and even in the capital itself. This extension is certainly partly due to the difficulty of implementing a ban on the exchange or transplanting of offshoots or ornamental adult palms as a rigorous prophylactic measure. Although the red palm weevil does not usually fly very much in the orchards where it is present, it probably flies to new orchards when, after killing all the existing date palms, it does not find enough food.
In Israel, early detection of the pest, when the number of affected trees was still very limited, resulted very quickly in the establishment of a program of integrated pest management. Substantial financial and human resources have been dedicated to avoiding the spread of the pest. Each new affected tree is immediately eliminated. More that 4000 pheromone traps have been located at a high density in 450 ha date plantations along the Jordan Valley. The incorporation of the systemic pesticide Confidor in the irrigation water has also been used. Despite all these efforts, newly infested trees are still being recorded, three years after the first detection of the pest, and red palm weevils are still being caught in traps.
All stages (egg, larva, pupa and adult) are spent inside the palm itself and the life cycle cannot be completed elsewhere. The females deposit about 300 eggs in separate holes or injuries on the palm. Eggs hatch in 2 to 5 days into legless grubs which bore into the interior of the palms, moving by peristaltic muscular contractions of the body and feed on the soft succulent tissues, discarding all fibrous material. The larval period varies from 1 to 3 months. The grubs pupate in an elongate oval, cylindrical cocoons made out of fibrous strands. At the end of the pupation period which lasts 14 to 21 days, the adult weevils emerge. Thus the life cycle is about 4 months.
Even when important and costly means are dedicated to combat the red palm weevil, an efficient solution to fight against it when it first arrives is still missing.
However, the main ornamental tall palms planted in the gardens and in the streets of the Mediterranean coast cities are date palms. Thousands of them are imported from Egypt each year directly or indirectly into Spain and other European countries. These palms must have a phytosanitary passport but in specimens such as adult date palms, a large quantity of hidden insects and diseases, can evidently remain undetected, even after very careful phytosanitary scrutiny, and this is, of course, the case with red palm weevil eggs and larvae.