NO EFFECTS OF SULFUR-DIOXIDE ON LARVAL PERFORMANCE OF EPIRRITA-AUTUMNATA (LEPIDOPTERA, GEOMETRIDAE)

Naturally growing ramets of mountain birch, Betula pubescens subsp. to rtuosa, enclosed in plastic chambers and fumigated with either ambient air or 1 of 4 SO2 concentrations (90, 210, 502, 810 mu g/m(3)) for 7 d were infested by last instars of Epirrita autumnata (Borkhausen) and fumigated for another 7 d. No larval mortality was observed during th e experiment. In chambers treated by SO2, larvae consumed less biomass but converted it more efficiently than in chambers filled with ambien t air. None of treatments deviated from control in either larval relat ive growth rate or pupal weight. However, pupae from chambers with 90 mu g/m(3) of SO2 gained approximate to 5% of weight compared with cham bers with 810 mu g/m(3) of SO2, indicating that zero net effect of hig her SO2 concentrations may appear because of the compensation of negat ive direct effects (toxicity) by positive indirect effects (improved q uality of fumigated plants).