Effects of pollutants on bottom-up and top-down processes in insect-plant interactions.
Pea aphids feeding from birth to maturity on pea plants (Pisum sativum) exposed to SO(2) concentrations of 50 nl litre(-1) or 80 nl litre(-1) showed a significant 19% increase in the rate of nymph production during the reproductive period, compared to control aphids feeding on plants in charcoal-filtered air. The higher nymph production resulted in a mean 4.6% increase in the intrinsic rate of population increase (rm). In longer term glasshouse fumigation experiments pea aphid populations were, on average, 1.8 times greater on pea plants in ambient air plus 45 nl litre(-1) SO(2) than in ambient air alone. Aphid infestation in ambient air caused a 42% reduction in pea yield and affected most plant parameters adversely. Ambient air plus SO(2) had no direct effect on yield, but, in combination with aphid infestation, a further 10% reduction in yield was recorded.