The influence of nitrogenous fertilizer on the grassland Auchenorrhyncha (Homoptera).
Samples of Auchenorrhyncha were collected from fertilized plots in southern England between April 1978 and November 1979. Twenty-nine species were recorded, of which 26 probably breed regularly on the experimental area. The addition of NPK fertilizer reduced leafhopper species diversity by disproportionately increasing the total number of individuals, which effectively reduced the equitability index. Delphacids were more abundant on plots receiving nitrogen fertilizer whereas cicadellids were more abundant on unfertilized areas. The major effect of nitrogen addition was to increase the food quality and the living area (plant architecture) available to leafhoppers. Both increased food quality and increased living area were beneficial to the leafhopper complex, allowing the community to increase rapidly in numbers (i.e. the total captured was 4122 in 1978 and 17 964 in 1979). Leafhoppers were more abundant on plots with 'preferred' leaf nitrogen level. Adult aggregation and female reproductive success were greater at the 'preferred' leaf nitrogen level.