Response of <i>Dendroctonus brevicomis</i> to different release rates of nonhost angiosperm volatiles and verbenone in trapping and tree protection studies

Abstract

Abstract A blend of eight nonhost angiosperm volatiles (benzyl alcohol, benzaldehyde, guaiacol, nonanal, salicylaldehyde, ( E )‐2‐hexenal, ( E )‐2‐hexen‐1‐ol and ( Z )‐2‐hexen‐1‐ol) without [NAV] and with [NAVV] (–)‐verbenone (4,6,6‐trimethylbicyclo[3.1.1]hept‐3‐en‐2‐one) were tested at low (L), medium (M) and high (H) release rates for their ability to reduce attraction of western pine beetle, Dendroctonus brevicomis LeConte, to attractant‐baited ( exo ‐brevicomin [racemic, 3 mg/d], frontalin [racemic, 3 mg/d] and myrcene [18 mg/d]) multiple funnel traps. NAV‐L (40 mg/d) had no significant effect. Verbenone alone (50 mg/d) and NAV‐M (240 mg/d) both significantly reduced attraction, but no significant difference was observed between the two treatment means. NAV‐H (430 mg/d) significantly reduced catches by ∼60% and 78% compared to verbenone alone and the baited control, respectively. In a second experiment, combining (–)‐verbenone with NAV (NAVV) increased the effects observed in Experiment 1. NAVV‐M (240 mg/d) resulted in an ∼69% and 83% reduction in trap catch compared to verbenone alone and the baited control, respectively. Significantly fewer D . brevicomis were captured in NAVV‐H (430 mg/d) than any other treatment resulting in an ∼93% reduction in trap catch compared to the baited control. In a third experiment, NAVV was tested at three release rates for its ability to protect individual ponderosa pines, Pinus ponderosa Dougl. ex Laws., from attack by D . brevicomis . Cumulative release rates varied in direct proportion to tree diameter, but represented quarter, half and full NAVV rates. NAVV significantly reduced the density of D . brevicomis attacks, D . brevicomis successful attacks, and levels of tree mortality on attractant‐baited trees. Only three of 15 NAVV‐treated trees died from D . brevicomis attack while ∼93% mortality (14/15) was observed in the untreated, baited control. Quarter and half rates were ineffective for reducing tree mortality.