The potential of three native insect predators to control the rosy apple aphid, Dysaphis plantaginea

The potential of three aphidophagous predators, Adalia bipunctata, Aphidole tes aphidimyza, and Episyrphus balteatus to control the rosy apple aphid, D ysaphis plantaginea Pass., a major pest on apple in Europe, was assessed by means of laboratory and field cage experiments in Northern Switzerland. Un der laboratory conditions, all three predators efficiently preyed upon D. p lantaginea on apple seedlings. The searching success of larvae of A. bipunc tata for individual aphids was not dependent on the size of branches of app le trees varying in leaf surface area from 150 cm(2) to 960 cm(2). Fifty an d 70% of individual aphids were found and killed 6 hours and 48 hours, resp ectively, after release of single second instar larva of A. bipunctata. In a first field cage experiment in 1996, A. bipunctata, and to a lesser exten t E. balteatus, proved to be effective and consistent predators of D. plant aginea during spring conditions, being little affected by cool temperatures and wet weather. In a subsequent field cage experiment in 1997, larvae of A. bipunctata and E. balteatus were released singly and in combination on a phid infested apple seedlings to study interactions between these two promi sing control agents. Both species had a significant negative effect on aphi d population increase. The two species did not significantly interact and t hus, their joint effect is best explained by an additive model. Combined re leases of the two predator species reduced aphid densities to 5% of the con trol. This indicates the potential for augmentative releases of these nativ e aphid predators to control D. plantaginea.