Attraction of invasive ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) to ethanol-treated tree bolts

Authors: Reding, Michael - Mike; Ranger, Christopher

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/21/2019
Publication Date: 11/6/2019
Citation: Reding, M.E., Ranger, C.M. 2019. Attraction of invasive ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) to ethanol-treated tree bolts. Journal of Economic Entomology. 113(1): 321-329. https://doi.org/10.1093/jee/toz282.
DOI: https://doi.org/10.1093/jee/toz282

Interpretive Summary: We tested the attraction of ambrosia beetles to sections of tree stems (bolts) treated with ethanol. Bolts were 1 to 2 inches in diameter by 8 to 12 inches long and cut from saplings. Ethanol-treated bolts may be more selective for damaging ambrosia beetles than ethanol-baited traps. Furthermore, bolts may be useful for screening insecticides against ambrosia beetles. Ethanol-treated and flood-stressed trees have been effective for attracting ambrosia beetles to test insecticides. However, using living trees to screen large numbers of insecticides is expensive and labor intensive. Bolts could be used to screen a variety of insecticides, then the most promising materials could be further tested on living trees. All tests included ethanol-baited traps to compare attraction and selectiveness of bolts versus traps (the standard monitoring tool). We tested two different techniques for treating bolts with ethanol, soaking and drill+fill. The drill+fill technique may be more compatible with screening insecticides than soaking. We also examined the time-period bolts were attractive and tested attraction of beetles to bolts from a variety of tree species. Xylosandrus germanus was the most common ambrosia beetle in all tests. Ethanol-soaked bolts were usually as attractive or more attractive to X. germanus, Xylosandrus crassiusculus, and Anisandrus maiche than traps. Bolts captured fewer species of ambrosia beetles than traps, indicating they were more selective for damaging species. The drilled+filled bolts were attractive to X. germanus and X. crassiusculus, but numbers were usually lower than in soaked bolts. None the less, attraction was sufficiently reliable to use drilled+filled bolts for screening insecticides. Bolts aged 14 days were not attractive, and attraction generally declined after 7 days of aging. Damaging ambrosia beetles were attracted to bolts from all species of trees tested (red maple, American elm, American hornbeam, black cherry, sassafrass, sycamore, sumac, flowering dogwood, and shingle oak), but X. crassiusculus did not occur in sycamore or oak. Attacks were easier to see on bolts with smooth bark than those with rough bark.

Technical Abstract: Ethanol-treated bolts (tree stem sections) have potential as monitoring and pesticide screening tools for ambrosia beetles (Coleoptera: Curculionidae: Scolytinae). Attacks on ethanol-treated bolts by Xylosandrus species was compared to captures in ethanol-baited traps. Bolts infused (immersed) in ethanol were usually as attractive or more attractive to Xylosandrus germanus (Blandford) than ethanol-baited bottle traps. Xylosandrus crassiusculus (Motschulsky) occurred in bolts in more experiments than traps, but numbers were low and differences were usually not significant. Two techniques for treating bolts with ethanol were compared. Drilled bolts filled with ethanol were attractive to X. germanus and were reliably attacked, but numbers of beetles were often lower than in infused bolts and traps. Aged and fresh ethanol-treated bolts were compared to evaluate residual attractiveness. Bolts aged 7 days usually had fewer X. germanus than fresh bolts and traps, and bolts aged 14 days had no beetles. Ethanol-infused bolts from different species of trees were compared. Xylosandrus germanus attacked all species tested with more attacks usually in red maple (Acer rubrum L.). Anisandrus maiche Stark was attracted to ethanol-infused bolts indicating it may attack trees emitting ethanol. Bolts attracted fewer non-target species than traps, but residual attraction was much less. The selectivity of ethanol-treated bolts for Xylosandrus species should make them useful for monitoring and screening pesticides against those species.