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Integrated control tactics for the New Guinea Sugarcane Weevil Rhabdoscelus

CIG Projects in PIA | Pacific Islands Area NRCS
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Integrated control tactics for the New Guinea Sugarcane Weevil Rhabdoscelus obscures

Grantee: University of Guam

Abstract:
The New Guinea sugarcane weevil, Rhabdoscelus obscurus (Boisduval) (Coleoptera: Curculionidae), is a native of New Guinea and the adjoining islands. It was originally described from specimens collected in New Ireland, Papua New Guinea and has since spread to many islands in the Pacific, including Australia and Indonesia. Dispersal of the weevil was almost certainly associated with inter-island trading of sugarcane in earlier years, but more recently palms introduced for the ornamental horticultural industry have become the most favored hosts for this weevil. On Guam, this weevil is a major pest of ornamental and other palms such as coconut palm (Cocos nucifera L.), betel nut (Areca catechu L.), champagne palm (Hyophorbe lagenicaulis (Bailey);), pritchardia palm (Pritchardia pacifica Seem. & H. Wendl.), pygmy date palm (Phoenix roebelenii O'Brien), Alexander palm (Archontophoenix alexandrae (F. Muell.) H. Wendl. & Drude), royal palm (Roystonea regia (Kunth) O.F. Cook and date palm (Phoenix canariensis Hort. ex Chabaud) as well as sugarcane (Saccharum officinarum L.). On palms, weevils lay their eggs in the petiole and on the stem. Larvae bore into the living tissue, producing frass filled tunnels that weaken affected parts of the host plant and permit invasion of fungal and bacterial pathogens. Mature larvae pupate in cocoons made of plant fibers close to the exit holes. Currently this weevil poses a serious threat to ornamental palms in the nursery industry and to betel nut production in Guam. Withdrawal of the ban on entry of betel nut into the U.S. mainland from Guam by the FDA has encouraged commercial cultivation of betel nut on Guam. Therefore, an effective management program for this weevil is urgently required.

Many of the farmers and house owners are spraying toxic pesticides such as dimethoate, acephate, malathion, carbaryl, dibrom and warrior to control this weevil. Since the grubs bore inside the plant stems, the chemicals do not affect the immature stages of the weevil. Usually as many as 20 to 30 sprays (average of 25 sprays) are applied each year, which is not only expensive in terms of financial outlay but also is associated with ecological and toxicological hazards. The existing pheromone-based trapping method is not very effective and resulted in low captures. No further studies have been carried out on the integration of pheromones and pathogens for control of this weevil.

We will work in collaboration with the Northern Marianas College, Saipan (CNMI). In this proposal we will try to (a) develop an efficient pheromone trap for catching weevils in field conditions, (b) develop traps based on Petri dishes with fungal spores (Beauveria bassiana and Metarhizium anisopliae) for auto dissemination through trapped weevils, (c) evaluate a mass trapping program in Rota (CNMI), (d) determine the effect of abiotic and biotic factors on the population dynamics of the weevil. Field demonstrations will showcase the achievements of the project to the public. The outlined technology is expected to be transferred to other Pacific islands and countries wherein attacks by R. obscurus are significant. Project results will be published in scientific journals and disseminated to farmers in the Marianas through extension units, the Guam Department of Agriculture, USDA-NRCS and local newspapers. The project coordinator and research team will give radio talks on the outcome of this research versus conventional pesticide application practices.