Dose reduction and alternatives to the phenol pheromone in monitoring and management of the grass grub Costelytra zealandica

Aimee R Harper, C Rikard Unelius, Richard J Townsend, David Maxwell Suckling

Endemic New Zealand grass grub Costelytra zealandica is a pest of introduced pasture that uses phenol as a sex pheromone. The pheromone could be used to monitor and manage grass grub populations, but the irritating properties and toxicity of phenol for human handlers, as well as the possible ecotoxicological effects, pose obstacles to the deployment of the pheromone. This study aimed to limit the use of phenol by dose-response studies and investigation into alternative attractants and synergists to phenol. No difference in trap catch was seen across the range of 1-100 mg of phenol, while rates below this (0.001-0.1 mg) caused a large drop in catches. Our results indicated that 1 mg loading in lures was enough to indicate beetle presence over one week. 4-Hydroxybenzaldehyde and p-cresol proved unattractive in this study, both as single attractants and as synergists with phenol. Phenyl acetate, phenyl benzoate and diphenyl carbonate all formed phenol under hydrolytic conditions to act as successful propheromones, while phenyl acetate was found to be as attractive as phenol on its own. This study described several ways to reduce or avoid the use of phenol in the field while maintaining lure effectiveness.