Predicting numbers of an insect (Neophilaenus lineatus : Homoptera) in a changing climate

1. Measurements of the density of an upland population of the spittlebug Ne ophilaenus lineatus (L.) (Homoptera, Auchenorrhyncha) were made from 1961 t o 1997. 2. Population change from year to year is shown to be largely density-indep endent. 3. Analyses of meteorological records over the 37-year period showed that t he weather variable with the highest correlation with population change was mean minimum temperature in September. 4. A simple model was constructed relating numerical changes from 1961 to 1 992 to temperature, and this was found to explain 75% of the change in this population. 5. The model was used to predict numerical change from 1993 to 1997 over wh ich period it explained 70% of the change. 6. The model predicts that a projected rise in mean temperature of 1 degree s C would increase the mean population density of N. lineatus by 50%. 7. Experimental cloches at the upland site which raised mean temperature by 1 degrees C, had N. lineatus densities which were 157% higher than in adja cent control quadrats. 8. An experimental raising of field temperature at a lowland site where pop ulation change had been shown to be density dependent did not result in den sity changes, although dates of hatching were earlier.