EFFICACY OF AN ANTIAGGREGATION PHEROMONE FOR REDUCING DOUGLAS-FIR BEETLE, DENDROCTONUS-PSEUDOTSUGAE HOPKINS (COLEOPTERA, SCOLYTIDAE), INFESTATION IN HIGH-RISK STANDS

The Douglas-fir beetle (Dendroctonus pseudotsugae) antiaggregation phe romone, 3-methylcyclohex-2-en-1-one (MCH), was applied to stands at hi gh risk for infestation. The MCH was applied in a bubble capsule formu lation to plots ranging from 2.1 to 2.6 ha in size at rates of 45 -76 g/ha. Catches of Douglas-fir beetles in attractant-baited Lindgren fun nel traps located at the plot centers were significantly lower on MCH- treated plots compared with untreated plots. In contrast, catches of t he most abundant predator, Thanasimus undatulus (Say), were unaffected by the MCH treatment. The percentage of Douglas-fir [Pseudotsuga menz iesii (Mirb.) France] trees greater than or equal to 20 cm dbh that we re mass attacked was significantly lower on treated plots (0.2%) compa red with untreated plots (8.5%), MCH alone was effective in reducing t he probability of Douglas-fir beetle infestations occurring in high ri sk stands.