Fungal, host and non‐host volatiles modify attraction of the walnut twig beetle, Pityophthorus juglandis, to pheromone lures

Abstract

Abstract Thousand Cankers Disease (TCD) of walnut trees is caused by the pathogenic fungus Geosmithia morbida vectored by the walnut twig beetle (WTB) Pityophthorus juglandis. Monitoring efforts for WTB rely on pheromone‐baited traps, but lures are likely effective at attracting beetles only over short distances. Fungal‐derived kairomones may increase the efficacy of current lures, while additional volatiles may repel beetles from valuable trees. The objective of this study was to determine the extent to which fungal, host and non‐host volatiles modify the attraction of WTB to pheromone‐baited traps. A trapping study that combined fungal, host‐associated and non‐host compounds with WTB‐pheromone lures was conducted over three years in black walnut plantations experiencing a TCD outbreak in Walla Walla, WA. Traps baited with pheromone and G. morbida volatiles (i.e., isoamyl and isobutyl alcohol) consistently attracted more WTB, while other fungal volatiles inconsistently increased attraction compared to those baited with pheromone lure alone. This is the first field study that demonstrates fungal volatiles can increase the attraction of a bark beetle to its pheromone in a hardwood system. One fungal (benzyl alcohol) and two additional volatiles (limonene, piperitone) repelled WTB from pheromone‐baited traps. Although limonene is known to repel WTB, this is the first demonstration that benzyl alcohol and piperitone repel a bark beetle. Fungal volatiles may increase the efficacy of monitoring efforts and may play an important role in management tactics for WTB, especially in detecting the introduction and establishment of nascent populations and protecting trees from colonizing beetles.