CONTRASTING EFFECTS OF SEWAGE-SLUDGE AND COMMERCIAL FERTILIZER ON EGGTO ADULT DEVELOPMENT OF 2 HERBIVOROUS INSECT SPECIES

Municipal sewage sludge containing heavy metals had a toxic effect on the development of the cabbage looper, Trichoplusia ni (Lepidoptera: N octuidae), one of two herbivorous insects commonly found in an Ohio ol d-field which had been subjected to long-term sewage sludge applicatio n. Soils were removed in 1992 from an old-field following 11 years of heavy nutrient enrichment (1978 to 1988) with applications of either s ewage sludge (Milorganite(R)) containing heavy metal contaminants or u rea-phosphate fertilizer. Egg to adult development rate and survival o f the blackfaced leafhopper, Graminella nigrifrons (Homoptera: Cicadel lidae), and the cabbage looper was determined on maize (leafhopper) an d broccoli (looper) seedlings grown in soils from sludge-treated, fert ilizer-treated, or untreated control plots of the old-field. Fertilize r and sludge-treated soils had higher levels of N, P and organic matte r, and a lower pH than the untreated control soils, while sludge-treat ed soils contained significantly higher concentrations of Cd, Cu, Pb, and Zn. Maize appeared to be unaffected by the three soil treatments, and survival and rate of egg to adult development of the leafhopper wa s not affected. Broccoli seedlings grown in both the high nutrient fer tilizer and sludge soils were greener and larger than broccoli grown i n control soils. However, the cabbage looper had significant larval an d pupal mortality (25 to 40%) and prolonged egg to adult development o n sludge-grown broccoli compared to control and fertilizer treatments. As assimilation into the food chain of heavy metals and other organic pollutants, such as PCBs, is in part a function of the interaction of soil chemistry and type of plant, the application of municipal sludge s to old-fields needs to be carefully monitored, as contaminants may h ave significant developmental and behavioural effects on some secondar y links in the old-field food chain.