Predation potency and intraguild interactions between generalist (Forficula auricularia) and specialist (Episyrphus balteatus) predators of the rosy apple aphid (Dysaphis plantaginea)

Abstract

To evaluate whether aphid antagonists are suitable targets for biological approaches to control aphid populations, their voracity and intraguild interactions must first be elucidated. The aim of this laboratory study was to compare two predators of the rosy apple aphid (RAA) Dysaphis plantaginea: the generalist Forficula auricularia and the specialist Episyrphus balteatus. Predation by 2nd and 3rd instar larvae of E. balteatus and 3rd and 4th instar nymphs of F. auricularia was evaluated individually and in combination for 24h in Petri dishes. Five different densities (25, 50, 75, 100 and 200) of 1st or 3rd instar nymphs of RAA were incubated at three different temperatures (15, 20 and 25°C). Overall, the older life-stages of both predator species were more voracious than younger individuals. The two predator species did not negatively interact. Instead, when the RAA density was not limiting they had an additive effect. Although the predators consumed significantly higher numbers of RAA when the younger life-stages were offered, they fed more efficiently on the older life-stages of RAA with consumption of 1.8- to 2.7-fold higher biomass. In general, the most RAA were consumed at 20°C. Syrphids consumed more RAA at 15°C than at 25°C whereas earwigs consumed slightly more aphids at 25°C than at 15°C. Overall, the two predators consumed a constant proportion of RAA at the first four RAA densities until reaching satiation. This finding suggests that in theory they would be effective in regulating RAA numbers in early spring when field RAA populations are beginning to build up. The potency of both predators, alone or in combination, should now be tested for augmentative approaches in semi-field and field studies.