Fungal and non-host volatiles modify the response of invasive ambrosia beetles to ethanol lures

Non-native ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) increasingly threaten the health and productivity of natural and planted forests worldwide, however effective tools and tactics to manage these pests remain elusive. Ambrosia beetles are intimately associated with symbiotic fungi that produce volatiles, but how beetles respond to these compounds is poorly understood. Semiochemical-based tactics employing fungal volatiles may improve detection and management efforts to decrease economic and environmental damage to forest resources.

We conducted field experiments to determine the extent to which fungal compounds, as well as several non-host compounds, modify the response of invasive ambrosia beetles to an attractant (i.e., ethanol). Our study focused on the response of three prevalent exotic ambrosia beetles: Xylosandrus crassiusculus (Motschulsky), Xylosandrus germanus (Blandford), and Xyleborinus saxesenii (Ratzeburg, 1837). Beetles were collected in bottle and multi-funnel traps baited with ethanol and fungal volatile lures in mixed-hardwood forests in Indiana over three years (2018-2020). Our results demonstrated that while individual fungal volatiles failed to increase attraction of adult beetles to ethanol lures, several compounds reduced the number of beetles captured. Both Xylosandrus species were repelled by isobutyl alcohol and benzyl alcohol, while X. crassiusculus was also repelled by isoamyl alcohol. Other fungal and non-host volatiles were inconsistently repellent to all three beetle species. Fungal and non-host volatiles may be used as cues to determine host suitability and thereby influence the response of colonizing females. The use of these repellants may hold promise to increase the efficacy of management tactics to protect vulnerable nursery stock and forest trees.