Inhibitory effect of monoterpenes on response of Pityogenes bidentatus to aggregation pheromone released by piezoelectric sprayer for precision release of semiochemicals

A piezoelectric sprayer for dispensing semiochemicals was developed and use d for a field test of bark beetle semiochemicals. The sprayer consists of a geared pump that pushes a syringe slowly to dispense semiochemicals in sol vents through a microtube to a glass micropipet fixed to a piezoelectric hi gh-frequency vibrator. The frequency is adjusted via a function generator t o about 120 kHz until the harmonic properties of the glass micropipet, draw n by an electrophysiological pipet puller, cause vibrations that atomize th e solvent from the micropipet tip. The sprayer, syringe, pump, function gen erator, and power supply were hung on one arm of a rotating trap pair (trap s 6 m apart) that was slowly rotated at 2 revolutions per hour (rph) to eve n out the position effects on trap catches. The aggregation pheromone compo nents of Pityogenes bidentatus, grandisol and cis-verbenol, were released b y standard tube dispensers in one trap and compared to the release of simil ar amounts by the sprayer in the other trap. No significant differences in catch were observed. No effect of the solvent hexane on aggregation could b e observed. The trap pair also caught approximately equal numbers of bark b eetles when the baits were identical. The release of (+)- and (-)-alpha-pin ene, (+)-3-carene, and terpinolene, monoterpenes of host Scotch pine, Pinus sylvestris, at increasing rates from 0.01 to 10 log-equivalents in decadic steps (each at 0.1-100 mu g/min) resulted in decreasing responses to aggre gation pheromone (only 9% at highest rate). Inhibition by the individual mo noterpenes tested at the 100 mu g/min rate was significant for (+)- and (-) -alpha-pinene and terpinolene (12, 13, and 15% of control, respectively). T he inhibition by the host Scotch pine monoterpenes may allow P. bidentatus to avoid resistant trees that release large amounts of toxic monoterpenes i n their resin and instead colonize dying and diseased limbs or slash, the u sual host substrate. The piezoelectric sprayer should prove generally usefu l to dispense precise amounts of semiochemicals in field and laboratory exp eriments.