The red palm weevil (Rhynchophorus ferrugineus Olivier, 1790) is a beetle belonging to the Dryophthoridae family.
From a systematic point of view it belongs to:
R. ferrugineus species.
The terms are synonymous:
– Calandra ferruginea Fabricius, 1801;
– Curculio ferrugineus Olivier, 1790;
– Rhynchophorus signaticollis Chevrolat, 1882.
Geographic Distribution and Habitat –
Rhynchophorus ferrugineus is a weevil native to Asia, which often affects and destroys many species of palm trees. The species concerned are various Arecaceae including the most common ornamental palms in the Mediterranean, Phoenix canariensis and Phoenix dactylifera, but also species of economic interest such as the coconut palm (Cocos nucifera) and the oil palm (Elaeis guineensis).
In detail, it is native to Southeast Asia and Melanesia, where it causes serious damage to coconut palm crops.
With the commercialization of infected palm trees, in the eighties it spread to the United Arab Emirates and from there to the Middle East (Iran, Israel, Jordan and Palestine) and to almost all the countries of the southern basin of the Mediterranean Sea (starting from Egypt where has been reported since 1992). From there it spread to Spain (first reported in 1994), Corsica and the French Riviera (2006).
In Italy it was reported for the first time in 2004 in plants from Egypt; in 2005 it was reported in Sicily and then spread rapidly towards the north of the peninsula: it arrived in Campania, where it destroyed hundreds of secular palm trees in public parks and private gardens; in Lazio, it returns to Tuscany and is finally also in Liguria, Marche, Abruzzo, Molise, Puglia, Basilicata, Calabria and Sardinia.
Also reported on the oceanic continent, the Netherlands Antilles and the United States in California.
The red palm weevil is a beetle that at the adult stage measures between 19 and 45 mm with a body width that varies between 11.5 and 15.5 mm.
The insect has a brownish-red livery, with black specks on the upper part of the thorax.
The rostrum is long and curved, more accentuated and covered by a thick brownish down in the male; the antennas are inserted at the base of the rostrum.
The elytra have a fine streak and are darker in color than the pronotum. The scutellum is about a quarter of the length of the elytra, rather broad.
Its eggs are thin, oblong in shape and creamy white in color; they measure on average 2.62 × 1.12 mm.
The larvae are 35 – 50 mm long; they have a whitish color and have a dark brown – brown head; the buccal and chewing apparatus is well developed and strongly chitinized. The body is white in color, consisting of 13 segments. The larvae are apods.
The pupa measures an average of 35 mm × 15 mm; this is initially creamy white to become brown in the more advanced stages.
Attitude and Life Cycle –
Rhynchophorus ferrugineus is a beetle that completes its cycle entirely inside the plant.
In this the female lays up to about 200 eggs at the base of the young leaves or on the wounds of the leaves or in the cavity of the palm trunk. The eggs are transformed in 2 or 5 days into small larvae that pierce the palms, feeding on the tissues of the same, eliminating all the fibrous material. The larvae move towards the interior of the palm by digging tunnels and large cavities.
The larval stage varies, also depending on the temperatures, from 1 to 3 months.
Subsequently, the larvae pupate in a cylindrical puparium formed by fibrous layers (generally this phase takes place outside the trunk, at the base of the plant). After 14-21 days the adults emerge.
The complete life cycle, from egg to fluttering, lasts an average of 82 days. Adults have a lifespan of around 2-3 months.
It has also been estimated that, in the absence of limiting factors, a single pair of Rhynchophorus ferrugineus can give life, over 4 generations, to about 53 million specimens.
Ecological Role –
Rhynchophorus ferrugineus is a beetle that has spread rapidly mainly due to the trade in palm specimens infested with the insect and not recognized as such.
Some species, such as the dwarf palm, were thought to be immune to infestation as it was thought that their gummy secretion could constitute a barrier against the rooting of the parasite, whereas it was found that they too are vulnerable to the weevil.
After the infestation this may not manifest itself (asymptomatic) except only in an advanced stage. The first symptoms are represented by an anomalous bearing of the crown, which assumes a characteristic “open umbrella” aspect. In the most serious cases, the leaves are completely lost, due to the collapse of the foliar rachis, so that the plant appears to be “decapitated”.
In the terminal stage of the infestation, therefore, a real “collapse” of the plant occurs: only at this point the colonies of the insect leave the attacked plant migrating to a new specimen.
Rhynchophorus ferrugineus adults are active both day and night. They are skilled flyers, able to reach new guests within 1km.
Due to its harmfulness, Rhynchophorus ferrugineus is considered a harmful organism subject to emergency measures by the European Community (Decision 2007/365 / EC “Emergency measures to prevent the introduction and spread in the Community of Rhynchophorus ferrugineus”) .
In Italy the DM 07/02/2011 “Provisions on the compulsory fight against the red palm weevil Rhynchophorus ferrugineus” is in force.
However, the containment measures of this insect are above all of a preventive nature as often the high aggressiveness of this insect makes curative intervention on symptomatic plants aleatory. Also because the control of Rhynchophorus ferrugineus is problematic and very difficult due to the contribution of multiple factors that favor the phytophagous. Adults move easily and can evade any protection or containment barriers by expanding outbreaks of infestation.
It should also be remembered that the choice of inserting native species instead of exotic Arecaceae within ornamental plants should always be considered.
Different prevention and control systems have been adopted in various states.
In India, for example, in date palm plantations, the method that seems to have given good results is the combination of several techniques: continuous monitoring of the plants, the use of pheromone traps for mass trapping of adults, treatment the wounds caused to the palms with insecticides, the filling of the axilla of the leaves with insecticides mixed with sand, the complete destruction of the most infested palms, the use of alternative techniques to fight with entomoparasitic nematodes.
In general, for the control of Rhynchophorus ferrugineus it is possible to carry out endotherapeutic phytosanitary interventions.
Chemical curative treatments must be performed with the use of systemic insecticides and an early diagnosis of the infestation.
Late interventions, in addition to being useless to resolve the attack in the infested plant, are also of little effectiveness. Preventive chemical treatments can have their effectiveness as a chemical barrier but require the use of contact active products, also endowed with a certain toxicity, and the coverage of the whole plant with spraying. The treatment of large specimens, which exposes them to the risk of drift phenomena, and the intervention in urban areas pose further constraints in the choice of the active principle, subordinating effectiveness to the protection of public health.
The use of natural antagonists is currently being studied in various research institutes.
However, the auxiliary arthropods have so far proved insufficient to contain the population dynamics. Better prospects can be obtained with the use of entomopathogens, in particular viruses agents of cytoplasmic polyhedrosis and nematodes. The effectiveness of the latter, at least in the experimental context, would have been highlighted by researches conducted in Spain in both preventive and curative use: the release of adults on plants previously treated with nematodes produced a mortality of 100%; it also seems that the nematodes are able to penetrate the tunnels and reach the larvae, thus allowing an intervention also in the curative setting.
As regards the use of traps, this has been widely tested in various regions of Asia, the Middle East and Spain; this method has highlighted the ancillary utility both in mass trapping and in monitoring the adult population. The indications reported in the literature on the degree of efficacy are discordant, however they highlight a greater efficacy of the use of combined attractants (pheromones and sugar-based food attractants) and the importance of the arrangement of the traps in relation to height.
In any case, the study and experimentation phase is still in the deepening phase.
In addition, there have been little results with the sterile male technique.
On the other hand, the adoptions of integrated pest management are more encouraging. However, this presupposes the adoption of combined techniques that act at various levels: population monitoring, use of mass trapping, examination of the palms for the purpose of early diagnosis, prophylaxis measures which consist in the elimination of possible reproduction sites, in the remediation of possible infestation outbreaks (eg abandoned gardens and palm trees), maintenance of plants in a good phytosanitary state, recourse to preventive and curative chemical treatments, recourse to regulations that impose phytosanitary measures, education and dissemination.
In addition, the literature also mentions the possibility of developing more or less unique early diagnosis methods, such as the use of dogs or the detection of the transpiration rate, which intensifies in infested palms.
In recently introduced environments, such as in Italy, prophylaxis is of fundamental importance in order to avoid the expansion of the phytophagus, intervening early on outbreaks of infestation. In this regard, on the basis of the objective difficulties in diagnosing attacks early and intervening with curative interventions, the following actions are of particular importance:
– monitoring by phytosanitary observers;
– the maintenance of palms in good nutritional and phytosanitary conditions, as the susceptibility to attacks by xylophagous insects increases in plants under stressful or otherwise weakened conditions;
– the adoption of pruning techniques and treatments that reduce the possible penetration sites of the insect;
– the destruction of outbreaks of infestation, represented by attached palms, adopting measures aimed at preventing the flicker of adults (removal of the palms, preparation of physical containment barriers, destruction with shredding and burning in a very short time).
It should also be remembered that the plants now destroyed must be chipped or shredded (possibly on site) and then incinerated in authorized sites. The site of destruction must be as close as possible to the site of the killing operations.
Furthermore, during transport, it is necessary to ensure that the load is not accidentally dispersed, therefore it must be carried out with closed or perfectly airtight means of transport using tarpaulins.
The resulting material obtained must have dimensions not exceeding 2 cm; depending on the characteristics it can be further treated with a contact insecticide, subjected to heat treatment (130 ° C for 3 minutes) or destined for composting centers, etc. Alternatively, it can be buried at least 3 m deep in an authorized landfill.
– Wikipedia, the free encyclopedia.
– Russo G., 1976. Agricultural Entomology. Special Part. Liguori Editore, Naples.
– Pollini A., 2002. Manual of applied entomology. Edagricole, Bologna.
– Tremblay E., 1997. Applied entomology. Liguori Editore, Naples.