Influence of heteropteran predators (Het., Anthocoridae, Miridae) on larval populations of hawthorn psyllids (Hom., Psyllidae)

Abstract

Abstract The relationship between hawthorn psyllids and their main natural enemies was studied in Upper Frankonia (Bavaria, Germany) for 4 years. Throughout this period, the most abundant psyllid species were Cacopsylla melanoneura and C. peregrina (Psyllidae) which passed through their larval periods on the hawthorn in spring. Only a few individuals of Cacopsylla crataegi were recorded, with a seasonal occurrence of the larval instars of this species in the summer months. Psyllid larvae were observed to be heavily attacked by a multitude of arthropod predators and psyllid densities on branches where predators had been excluded were significantly higher than on branches with predators present. The heteropterans Anthocoris nemorum, A. nemoralis (Anthocoridae) and Atractotomus mali (Miridae) were considered to be the most important natural enemies of hawthorn psyllids; they regularly reached high densities on hawthorn shrubs and showed a close synchronization with the development of psyllid larvae in each year. All three species exhibited a positive numerical relationship with the abundance of psyllid larvae with A. nemoralis and A. mali exploiting this food resource more effectively than A. nemorum , which is known to be a very polyphagous species. Despite high predation pressure on psyllid larvae, it is concluded that these heteropteran predators are not able to prevent outbreaks of psyllids under favourable climatic conditions as their numerical response to growing psyllid densities occurs with a distinct time delay.