Pheromone trapping of the sugarcane weevil borer, Rhabdoscelus obscurus (Boisduval) (Coleoptera: Curculionidae): an evaluation of trap design and placement in the field

Abstract  The sugarcane weevil borer ( Rhabdoscelus obscurus ) is a pest of sugarcane and palm plantations in high rainfall areas of far north Queensland. Pheromone mass trapping of adult borers is an effective method of monitoring and may also impact on their population densities. Trials to evaluate different designs of pheromone trap showed the 'water trap' to be the most effective in capturing the highest number of adult borers. The water trap is a 20 cm-diameter pot with a plastic bag inserted to hold water with pheromone lures and cane pieces held together in a plastic container suspended over the water from a square of wire mesh. Results also showed that adult borers in adjacent fields are able to sense the lures and migrate into treated fields. The sex ratio of captured borers in split-cane traps (which is a standard population monitoring tool) was male biased from February to April but was more balanced later in the year. However, the pheromone traps mainly attracted female borers all year round, except during May. Thus, we recommend pheromone traps to be deployed early in the season (November to early December) to attract the maximum number of adult females at a critical time for the population as it starts to build up. In addition, placing pheromone traps inside cane paddocks did not improve the total catch in most cases. Therefore, placing pheromone traps under the shade of trees outside the paddock or at the edge of the paddock under sugarcane can be a feasible mass trapping method that can easily be implemented by cane growers.