BIOLOGY AND CONTROL OF PALM WEEVIL Rhabdoscelus maculatus IN FOLIAGE NURSERIES

Abstract

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A study on the Biology and control of palm weevil Rhabdoscelus maculatus was carried out at Tropiflora ornamental palm nurseries in Sri Lanka. This weevil, an important pest of ornamental palms, was recorded for the very first time in Sri Lanka at Tropiflora Nurseries. Although the incidenceof this weevil is restricted to ornamental palms at present, there is a very realistic threat of it becoming a pest of important cultivations such as coconut and sugarcane. The present investigation was therefore, carried out with the view of confirming the identification of weevil, studying its biology and ultimately finding a suitable, environmentally friendly method for its control. Biological, morphological and behavioural aspects of the weevil were studied under laboratory, semi-natural and natural conditions. The adult is a small, reddish-brown weevil with two black markingson the elytra and the thorax. Mature female weevil lays eggs inside cavities made in the leafsheath. Under laboratory conditions, period for egg incubation was 5.00 ± 0.82 days. The larva is creamy white, legless grub with rounded, highly sclerotized, reddish brown head capsule. The frequency distribution analysis of head capsule width revealed six larval instars. Early weevil infestationof palms is indicated by a jelly like substance oozing from the holes in the leaf sheaths. R. maculatus larvae take about 7.75± 3.70weeks to complete its development and they pupate insidea cocoon made with tightly bound, fibrous material in 2.50 ± 0.76 weeks. The total life cycle of this weevil is completed in 10-12 ~s and observations of its life cycle in palm fields indicatedfour generations per year. The life span of adult weevils is between 8-10 months under semi-naturalconditions. The femaleweevil preferred Crysolidocarpus lutescens most for oviposition followed by Livistonia rotundofoliaand Saccharum ofJicinarum respectively. However, host acceptability in the case of Cocosnucifera was zero. The aggregation pheromone of the sugarcane weevil R. obscurus, (E2)-6-methyl-2-hepten-4-ol & 2-methyl-4-octonol(Rhynchophorol) and 2-methyl-4-octanol, was found in this study to be highly effectivein attracting R. maculatus. Plastic bucket-traps baited with the aggregation pheromone in combinationwith plant kairomones (ethyl acetate and cut sugarcane) captured significantly more weevilsthan traps baited with the combination of pheromone and sugarcane or individual lures alone. In the field, such traps were effective in attracting weevils throughout the one month experimentation period. The Trapping-out strategy using different combinations of lures almost completely brought down the palm weevil population to an extremely low level in the field. Significantly,in this study, pheromone and kairomone combination was found to be the most efficaciousagent for capture of adult weevils. The overall results of this study demonstrate amply that this trap-out strategy using the aggregation pheromone and host kairomones could be successfullyincorporated into Integrated Pest Management (IPM) programmes to suppress palm weevilpopulations.