Enhanced pheromone-based trapping method for New Guinea sugarcane weevil, Rhabdocelus obscurus (Coleoptera: Curculionidae)

The New Guinea sugarcane weevil Rhabdocelus obscurus (Boisduval) (Coleoptera: Curculionidae) is native to New Guinea and its adjoining islands. 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, betel nut, champagne palm, pritchardia palm, pygmy date palm, Alexander palm, royal palm and date palm as well as sugarcane. In addition, the pheromone-based trapping method using bucket traps typically results in low capture rates. Among the existing control methods of the pest, chemical application is both undesirable and expensive. In this study, several important factors that affect pheromone-based catches, such as types of traps, trap dimensions, color and position of the traps have been optimized. Ramp traps baited with pheromone lures have been found to be superior to ground and pitfall traps, and traps with larger dimensions (40 × 25 cm) were more efficient that those with smaller dimensions (30 × 15 cm). In a color-choice test, the weevil clearly preferred brown traps over yellow, red, gray, blue, black, white and green. Therefore, brown colored ramp traps of 40 × 25 cm appear to be very efficient in catching Rhabdocelus obscurus adults.