Survey for attraction-inhibiting semiochemicals for <i>Ips grandicollis</i> (Coleoptera: Curculionidae) in its native and invasive ranges

The eastern 5-spined ips, Ips grandicollis (Eichhoff), is native to the eastern USA and is an invasive pest of exotic pines (Pinus spp.) in Australia. It can kill stressed trees and transmit ophiostomoid fungi that cause blue staining of wood and reduce the commercial value of timber. Ips grandicollis uses semiochemicals produced by conspecifics to locate mates, while semiochemicals from competitors and nonhosts may reduce the reaction to attractants. To investigate methods to exploit these behaviors in a management strategy, we evaluated the impact of 12 potential semiochemical inhibitors of I. grandicollis attraction using traps baited with aggregation pheromone (ipsenol and cis-verbenol) in the beetle's native (northeast Georgia and central Louisiana, USA) and invasive (southeast Queensland, Australia) ranges over 2 yr. In the first trapping experiment (2022 to 2023), 2 semiochemicals (2-phenylethanol and methyl eugenol) significantly decreased attraction to the lure by 35% to 39% in the native range and 55% to 56% in the invasive range. Camphor reduced trap catches in Louisiana (26%) and Queensland (41%) but not in Georgia. In the second experiment (2023 to 2024), the inhibitory effects of methyl eugenol, 2-phenylethanol, and camphor were tested alone and in binary and ternary combinations. The binary combination of methyl eugenol and 2-phenylethanol reduced attraction by 66% in Georgia. However, such differences were not observed in Louisiana. The ternary combination of these compounds reduced attraction by 76% in the invasive range. Further research on these inhibitors could lead to a sustainable push-pull management strategy for protecting pine trees and log stacks from I. grandicollis attacks.