Effects of Air Pollution on Herbivorous Insects

The effects of air pollution on vegetation, in particular reduction in the economic yield of crops have been studied for many years. Various estimates have been made of the economic impact of different pollutants in this respect in both USA and Europe, while more recently interest has started to grow in developing countries (Ashmore et al., Shamsi et al., this volume — Chapters 3 & 6, respectively). The best estimate of such effects was produced by the USA National Crop Loss Assessment Network (NCLAN) programme, carried out in the 1980s. This employed a rigorous common protocol in which experimental plants were grown to maturity in open-top chambers ventilated with air containing a range of 03 concentrations in order to generate dose/response relationships. On the basis of the NCLAN study it was estimated that the current direct economic impact of O3 alone on the ten most important crops in the USA amounted to about $ 3 x 109 per year (Adams et al., 1988). This was equivalent to about 2.8% loss on annual production over the country as a whole. However, comparison with losses due to other stresses indicates that the latter are of a considerably greater magnitude, e.g., a 33% reduction in the annual production in USA resulting from attack by fungal pathogens and insect pests (Bell et al., 1993).