INFLUENCE OF HETEROPTERAN PREDATORS (HET, ANTHOCORIDAE, MIRIDAE) ON LARVAL POPULATIONS OF HAWTHORN PSYLLIDS (HOM, PSYLLIDAE)

The relationship between hawthorn psyllids and their main natural enem ies was studied in Upper Frankonia (Bavaria, Germany) for 4 years. Thr oughout this period, the most abundant psyllid species were Cacopsylla melanoneura and C. peregrina (Psyllidae) which passed through their l arval periods on the hawthorn in spring. Only a few individuals of Cac opsylla crataegi were recorded, with a seasonal occurrence of the larv al instars of this species in the summer months. Psyllid larvae were o bserved to be heavily attached by a multitude of arthropod predators a nd psyllid densities on branches where predators had been excluded wer e significantly higher than on branches with predators present. The he teropterans Anthocoris nemorum, A. nemoralis (Anthocoridae) and Atract otomus mall (Miridae) were considered to be the most important natural enemies of hawthorn psyllids; they regularly reached high densities o n hawthorn shrubs and showed a close synchronization with the developm ent of psyllid larvae in each year. All three species exhibited a posi tive numerical relationship with the abundance of psyllid larvae with A. nemoralis and A. mali exploiting this food resource more effectivel y than A. nemorum, which is known to be a very polyphagous species. De spite high predation pressure on psyllid larvae, it is concluded that these heteropteran predators are not able to prevent outbreaks of psyl lids under favourable climatic conditions as their numerical response to growing psyllid densities occurs with a distinct time delay.