Spatial and Climatic Factors Influence Ambrosia Beetle (Coleoptera: Curculionidae) Abundance in Intensively Managed Plantations of Eastern Black Walnut

Invasive ambrosia beetles are among the most economically important pests of forest and plantation trees world-wide. The development of effective management guidelines for these pests in plantations of high-value hardwood species is hindered by a lack of baseline information regarding their seasonal abundance and dispersal behavior. By analyzing long-term monitoring data from intensively-managed plantations of eastern black walnut (Juglans nigra L.) in north-central Indiana, we identified key spatial and climatic variables that could improve the timing and precision of management actions to reduce ambrosia beetle populations. We also used geospatial analyses to compare species-specific spatial patterns of population density and evaluate the sensitivity of the trap density deployed in our long-term monitoring efforts. Xyleborinus saxesenii Ratzeburg and Xylosandrus crassiusculus Matschulsky (Coleoptera: Curculionidae) were more abundant during the spring in years preceded by a hot, dry growing season, and cold winter. Both species were positively associated with plantation edges during the fall flight period. However, X. saxesenii was less abundant in plantations close to forest corridors, whereas X. crassiusculus was more abundant in plantations closer to woodlots and other walnut plantations. Geospatial analysis revealed X. crassiusculus is active in larger, more spatially continuous patches than X. saxesenii, and that 200-m trap spacing is likely to be sufficient to detect both species in the spring flight period but may be insufficient to detect X. saxesenii during the fall flight period. Our findings underscore the power and utility of long-term monitoring to improve management strategies.