Olfactory response of eastern spruce budworm larvae to red spruce needles exposed to acid rain and elevated levels of ozone.

Second-instar eastern spruce budworm larvae,Choristoneura fumiferana (Clem.), were tested in a two-choice, Y-type, wind-tunnel olfactometer for preferences for red spruce,Picea rubens Sarg., needles exposed for eight weeks to charcoal-filtered air (CFA) or 0.15 ppm ozone (O3) in combination with acidified rainfall at pH 4.2 or 3.0. Volatiles from needles treated with CFA plus pH 4.2 rain (control) were preferred over those from needles exposed to pH 3.0 rain + O3 or O3 alone; O3-treated needles were chosen over those exposed to pH 3.0 rain + O3. No preference was shown between the pH 4.2 and 3.0 rain treatments. Larvae chose purified air flowing through the olfactometer in preference to needle volatiles from the pH 3.0 rain + O3 treatment.