EFFECTS OF GASEOUS AIR-POLLUTANTS ON APHID PERFORMANCE ON SCOTS PINE AND NORWAY SPRUCE SEEDLINGS

Aphids are frequently found on conifers, but mass outbreaks are seldom reported. On trees stressed by air pollutants the natural resistance can be broken and insect attack combined with pollution stress may pro mote plant damages. To evaluate effects of air pollution on conifer ap hids Scots pine and Norway spruce seedlings have been exposed to gaseo us pollutants (O-3, SO2 and NO2) in growth chambers. The studied aphid species were Cinara pilicornis Hartig on Norway spruce, C. pinea (Mor dv.) and Schizolachnus pineti Fabr. on Scots pine in SO2 fumigations a nd S. pineti in O-3 and NO2 fumigations. C. pilicornis nymphs had peak ed dose response to SO2 concentration. Both the first and third instar larvae of C. pilicornis showed highest mean relative growth rate (MRG R) at 100 ppb SO2 concentration. MRGR of C. pinea peaked at 50 and 156 ppb SO2. The response of S. pineti was more inconsistent During fumig ation the peak MRGR of S. pineti was at 100 ppb and after exposure at 50 ppb SO2 MRGR of S. pineti nymphs was not significantly affected dur ing fumigation or after the end of fumigation experiment by 100 ppb O- 3 or 100 ppb NO2 or the mixtures. The results suggest that SO2 affects more distinctively on aphid performance on conifers than O-3 or NO2. Especially stem-feeding aphids on spruce can exploit physiological dis turbance of host plant under pollutions stress.