Exotic Weevil Threatens Local Palms
By Vincent Lazaneo
The Red Palm Weevil (RPW), Rhynchophorus ferrugineus is the most destructive insect pest of palms in the world. In August 2010, this weevil was found for the first time in the United States in a dying canary island date palm at a residence in Laguna Beach. Agriculture officials visually surveyed palms in the surrounding area and set out pheromone traps to determine the extent of the infestation. Steps will be taken to try to eradicate the infestation.
Establishment of RPW in Southern California would threaten the state’s 30 million dollar date palm industry and many ornamental palms planted in landscapes throughout southern California. The weevil’s primary hosts are palms including some common, local landscape species: queen palm, fishtail palm, Canary Island date palm, Chinese windmill palm and Mexican fan palm (the California fan palm is reported to be resistant to the pest). Secondary hosts of the weevil include American agave and sugarcane.
Residents of San Diego County who have landscape palms should watch for signs of RPW and report possible infestations to the County Agriculture Dept. at (858) 694-2739. When you have a palm trimmed, ask the arborist to inspect the tree’s crown for signs of damage. Early Red Palm Weevil infestations can be difficult to detect in large palms in the landscape unless access to the actively growing portions can be attained.
Symptoms: It is important that arborists and individuals working in palm canopies be vigilant for signs of larval mines and frass (excrement) in leaf bases in the central growing point of the palm in order to detect signs of early infestation. Larval damage to leaf bases anywhere in the canopy revealed by routine trimming may also be a sign of feeding by young RPW larvae. Dieback in the apical (newest, uppermost, or center) leaves in the canopy is a common symptom of larval damage to the meristem tissue and should be investigated for RPW. Frass accumulating at points of injury or at the base of offshoots may also appear in infested trees.
Palms damaged by RPW can exhibit the following symptoms:
Identification: Adult Red Palm Weevils are very large beetles, attaining body lengths of 1.4 to1.6 inches. The weevils have a long, slender snout which the female uses to penetrate palm tissue and create access wounds in which eggs are deposited.
Coloration in RPW is extremely variable. Adult weevils are predominately reddish-brown in the most typical form. The Red Palm Weevils collected in Laguna Beach have displayed a distinct “red striped” coloration which consists of the dorsal (top side) surfaces appearing uniformly dark brown to black, with a single, contrasting red stripe running the length of the pronotum (top,middle surface of the body between the head and abdomen). Visit www.cisr.ucr.edu to see photos. 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 (four life stages), with larvae and pupae developing within the trunk and apical growth tissues of the palm. Larvae are legless grubs with the body color uniformly pale yellow with a brown head. They may attain lengths greater than 2 inches. The larvae feed within the soft tissues of the growing tip (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 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 snout, or rostrum, to chew a hole into palm tissue. Eggs are then laid into this hole. Eggs may also 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 to 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 larvae form tunnels as they feed which contain frass (excrement and chewed fibers that have a highly distinctive odor) and plant sap. Larvae may pass through 3 to 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 Weevils emerge from cocoons and live for 2 to 3 months feeding on palms, and going through several cycles of mating and egg laying before dying. Females can lay eggs for 8 to 10 weeks.
The adult weevils are strong flyers. They can fly up to a half a mile at a time and can move up to four miles in 3 to 5 days. RPW has also been transported very long distances through the international trade in live palms. It can easily be moved as eggs, larvae or pupae, hidden in infested palms. RPW is native to Southeast Asia and is widespread in the region. The weevil has also spread to Africa, the Middle East, southern Europe, Australia and other South Sea Islands and Aruba in the Caribbean.Vincent Lazaneo is Urban Horticulture Advisor for UC Cooperative Extension. He helped found the San Diego County Master Gardener Association more than two decades ago and serves as its advisor. He is the author of numerous articles on plants and pests that appeared in the San Diego Union-Tribune, California Garden and other publications.
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