|An adult Red Palm Weevil (Rhynchophorus ferrugineus)|
This blog post is about an insect known as the Red Palm Weevil (Rhynchophorus ferrugineus) widely considered to be the most destructive insect pest of palms in the world. The above photograph showing the adult Red Palm Weevil (RPW) was taken by my husband in Malta in 2011. This insect which is originally native to South East Asia is spreading all over the world at an alarming rate and leaving behind it a devastating trail of dead palm trees. It is my hope that by drawing attention to the Red Palm Weevil in my blog I will be able to inform people and raise awareness. The Red Palm Weevil has been recorded throughout the Maghreb region of North Africa including Tunisia.
Aside from the aesthetic beauty of palm trees in urban amenity horticulture, the date palm (Phoenix dactylifera) carries a huge economic importance in terms of date production to the world economy including the Tunisian economy. Statistics from the Food and Agriculture Organisation in the year 2000 show that Tunisia is in the top ten of leading date exporting countries http://www.fao.org/docrep/006/y4360e/y4360e07.htm. Tunisia exports a variety of date called Deglet Noor (Arabic: دڤلة النور date of light).
Having emphasised the importance of palms not only to Tunisia but to other countries around the world, let us now try and learn a little more about the Red Palm Weevil. In my research on the internet, I came across an excellent and informative website by the University of California, Riverside, Center for Invasive Species Research (CISR). I contacted all three authors of this research and Dr Mark S. Hoddle Director of Center for Invasive Species Research, Extension Specialist, Department of Entomology kindly got in touch with me and granted me permission to use copyright protected text and photographs from their website in my blog post about the Red Palm Weevil with the aim of educating and informing the international readership of my blog. My thanks to him and to his colleagues for their continuing research into this insect.
Identification: Adult Red Palm Weevils are very large beetles, attaining body lengths, including the rostrum of 35 to 40mm (1.4-1.6 inches). The weevils have a long, slender rostrum or “snout” which the female uses to penetrate palm tissue and create access wounds in which eggs are deposited. Coloration in Rhyncophorus ferrugineus is extremely variable and has historically led to the erroneous classification of color-defined polymorphs (variants) as distinct species. Coloration in the adult weevils is predominately reddish-brown in the most typical form. The Red Palm Weevil’s collected in Laguna Beach have displayed a distinct “red striped” coloration which consists of the dorsal surfaces appearing uniformly dark brown to black, with a single, contrasting red stripe running the length of the pronotum. Consequently, there are two different color types or color morphs for RPW, adults that are predominantly reddish in color, and the others that are dark with a red streak, like the Laguna Beach specimens. The Red Palm Weevil, like other beetles, develops through complete metamorphosis, with larvae and pupae developing within the trunk and apical growth tissues of the palm meristem. Larvae are legless grubs with the body color uniformly pale yellow with a brown head. Larvae may attain lengths greater than 50 mm (2 inches). Larvae feed within the soft tissues of the meristem or leaf bases creating frass filled mines, enlarging and penetrating deep within the upper trunk areas as the larvae mature. Mature larvae construct a pupal chamber or cocoon made up of coarse palm fibers in which they pupate and occupy for approximately three to four weeks. The cocoons are located within the damaged tissue of the palm.
Life Cycle: To lay eggs, females use their long beak, or rostrum, to chew a hole into palm tissue. Eggs are then laid into this hole. Eggs may be laid in wounds, cracks, and crevices in the trunk, from the collar region near the roots, up to the base of frond petioles and axils near the crown of the palm. Females can lay 58-531 eggs which hatch in about 1-6 days. Larvae that hatch from eggs, feed on the surrounding palm tissue and bore their way into the center of the palm. The tunnels larvae form as they feed fill with frass (excrement and chewed fibers that have a highly distincitve odor) and plant sap. Larvae may pass through 3-7 instars or stages that may last for about two months before the pupal stage is reached. Larvae pupate inside cocoons in the palm trunk, or in concealed places at the base of palm fronds. The pupal stage may last from 11 to 45 days. The entire life cycle, egg to adult, can take 45 to 139 days. Adult Red Palm Weevil emerge from cocoons, and females can lay eggs for around 8 to 10 weeks. Adult weevils live for about 2 to 3 months feeding on palms, and going through several cycles of mating and egg laying before dying. The sex ratio is slightly biased towards females (1 male to about 1.2 females). In Egypt, it has been estimated that RPW can have up to 21 generations per year. This pest can be reared in the laboratory on sugar cane, and a variety of artificial diets.
Control Options: Suppression of Red Palm Weevil infestations can be attempted in several ways. Insecticides are probably the most common control tool used against Red Palm Weevil, and can applied in a variety of ways for RPW suppression including applications as dusts, liquid sprays. Trunk injections or soil applications of systemic insecticides that move inside the palm poisoning weevil larvae and adults may also be effective. Good sanitation practices are needed to prevent Red Palm Weevil spreading from infested palms. Chipping, burning, and burying infested material deeply can reduce the likelihood that Red Palm Weevil will emerge and escape from infested palms. Mass trapping has been used to reduce Red Palm Weevil densities. In this instance, aggregation pheromones are loaded into bucket traps along with palm material and granular insecticides. RPW adults are attracted by the pheromones and the plant material and fly into buckets. Once inside the bucket trap, the pesticide kills the weevils before they can escape. Biological control is the use of natural enemies, like predators, parasites, and pathogens to kill a pest. Red Palm Weevil is attacked by a variety of different natural enemies including parasites and small predators that attack weevil eggs, while bacteria, fungi, and nematodes can kill weevil larvae. Many of these biological control agents do not provide adequate control of Red Palm Weevil in the field. Host plant resistance can reduce the ability of Red Palm Weevil to damage palms because the weevil is unable to effectively exploit these hosts. The California fan palm, Washingtonia filifera, which is native to southern California and western Arizona, and the European fan palm, Chamaerops humilis, appear to be resistant to Red Palm Weevil infestations.
For latest news on Red Palm Weevil, visit the CISR blog