Developing a push-pull semiochemical pest management strategy for control of Ips grandicollis (Coleoptera: Curculionidae: Scolytinae) in pine plantations

Somia Afzal

doi:10.25907/01002

Exotic pines (Pinus spp.) are planted commercially in Australia as a source of softwood timber used for sawlogs, engineered wood products, poles, girders, and pulp and paper. The bark beetle Ips grandicollis (Eichhoff) (Coleoptera: Curculionidae: Scolytinae) is a significant invasive pest of these softwood plantations, particularly when trees are stressed, during drought, or following fire. The beetle is native to eastern North America and spends much of its life within the phloem, or beneath the outer bark, of host trees, to which it transfers mutualistic fungi that block conductive tissue and cause blue staining, reducing the commercial value of the wood. Adult beetles use volatile semiochemicals as cues for host location and communication. For example, aggregation pheromones and host volatiles induce attraction (pull), whereas semiochemicals from competitor species and non-host plants may induce an avoidance (push) response. This thesis investigated the semiochemical-based push-pull technique as a potential eco-friendly management strategy for I. grandicollis, with the overarching goal of protecting Pinus trees and logs from beetle attacks. Through a meta-analysis of 863 experiments over 32 years, I found that candidate semiochemicals used in a push-pull approach reduced the number of beetles caught at lures and tree attack/mortality from Ips spp. by an average of 66%, compared to controls. This estimate reflects meta-analysis results and confirmed that conspecific and heterospecific volatiles, non-host volatiles, and repellent host volatiles all reduced Ips populations and, therefore, were potential candidate compounds for developing a push-pull management strategy. Volatile profiles of seven isolates of four I. grandicollis-associated ophiostomatoid fungi -Ceratocystiopsis sp., Ophiostoma ips, Sporothrix pseudoabietina, and Graphilbum ipis-grandicollis - were examined for up to 18 days, with and without supplemental host monoterpenes (α- and β-pinene). Twenty-one volatile compounds were identified, including two associated with aggregation (cis-verbenol) and anti-aggregation (verbenone) in the Ips genus. 2-phenylethanol, an aromatic alcohol that mediates ecological interactions between beetles, was also produced, reflecting the potential contribution of ophiostomatoid fungi to the chemical ecology of I. grandicollis. Twelve semiochemicals, identified from the meta-analysis, fungal volatile analysis, literature, and preliminary laboratory studies as putative repellent compounds, were assessed for their effect on I. grandicollis aggregation behaviour. In a field experiment, funnel traps were baited with a lure (ipsenol and cis-verbenol), either alone (control) or in combination with one of the 12 test compounds in the native range (northeast Georgia and central Louisiana, United States of America (USA)) and invasive range (southeast Queensland, Australia) of the beetle. Of those tested, two semiochemicals—2-phenylethanol and methyl eugenol—significantly decreased I. grandicollis attraction to the lure in both the native and invasive ranges. Camphor also reduced trap catches in Louisiana and Queensland but not in Georgia. Based on these results, the potential for a synergistic effect of methyl eugenol, 2-phenylethanol, and camphor in all possible combinations was tested in a second field experiment. 2-phenylethanol/methyl eugenol in a binary combination showed a significant reduction in trap catch compared to the control at all sites. A ternary combination of 2-phenylethanol/methyl eugenol/camphor reduced I. grandicollis attraction to the lure by up to 76% in the invasive range, indicating the potential of these compounds to protect trees and log stacks. My meta-analysis revealed that semiochemical deterrents significantly reduced the frequency of Ips males (the pioneer sex that initiates attacks on trees). This was tested by comparing sex ratios of beetles trapped in the field and undertaking laboratory beetle behavioural observations in the presence of test compounds. Trap catches were always significantly female-biased, but traps baited with camphor proportionally decreased males compared to the control in the first field experiment. Y-tube olfactometer results were inconsistent with field trial results, highlighting the importance of testing compounds in a real field environment, rather than relying solely on laboratory experimentation. To test the best candidate repellents in the field, a small-scale log stack study was carried out using the three compounds that reduced lure attraction most effectively in the previous trapping experiment. The combination of 2-phenylethanol, methyl eugenol and camphor as the “push” and ipsenol and cis-verbenol-baited traps as the “pull” showed no difference in I. grandicollis attack and blue stain severity from control logs. This highlights the need for further research to test these compounds under different application methods and release rates to clarify their effectiveness. This thesis demonstrated the potential of semiochemical-based control, broadly, from meta-analysis results of Ips spp., to the identification of compounds specifically aimed at controlling I. grandicollis. It also expanded our understanding of potential management strategies for I. grandicollis by revealing the identity of semiochemicals from associated fungal species. This highlighted differences in I. grandicollis' responses to semiochemicals under laboratory and field conditions, as well as the reduction in lure attraction during trapping experiments in its native and invasive ranges. These findings contribute to future research aimed at equipping forest managers with tools for Ips management, particularly under climate change scenarios involving more frequent fires and droughts.

Developing a push-pull semiochemical pest management strategy for control of Ips grandicollis (Coleoptera: Curculionidae: Scolytinae) in pine plantations

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