Factors Affecting Gastrophysa viridula Populations (Coleoptera: Chrysomelidae) in Different Habitats

Abstract

The effect of habitat on the populations of G. viridula feeding on Rumex obtusifolius was studied in a range of habitats including meadow and 3 experimental plots with varying background vegetation. The most numerous predators were spiders and predatory Heteroptera. They were most abundant on the experimental plots with mature and diverse vegetation. Dispersal of adult beetles from a central release point was measured on the diverse vegetation plot. There was active redistribution of beetles within the plot but relatively little emigration. Approximately 3/5 of the adult population was moving between plants on the plot at any given time. The mean time for each beetle to find a new plant was < 1 day. On the hay meadow, food quantity declined during the season and the mean age of the leaves on which the beetles were feeding increased (implying a reduction in food quality). Consumption of foliage by the beetle on the hay meadow was estimated to be 45% of the peak standing crop of dock leaves. G. viridula completed 3 generations on the cut meadow. There was no 3rd generation of adults on the uncut hay meadow in 1974 and no 2nd or 3rd generations on the diverse and mature plots in 1975. This was because there was no suitable food available at these times. G. viridula survives best on communities at an early successional stage. Populations on hay meadows depend on periodic mowing or grazing to prevent the dock population becoming synchronized in seed production and leaf loss.