Effects of augmentative releases of eggs and larvae of the ladybird beetle, Adalia bipunctata, on the abundance of the rosy apple aphid, Dysaphis plantaginea, in organic apple orchards

The impact of augmentative releases of larvae and eggs of the indigenous la dybird beetle Adalia bipunctata (L.) (Coleoptera: Coccinellidae) against th e rosy apple aphid Dysaphis plantaginea Pass. (Homoptera: Aphididae), a maj or pest insect on apple trees, was assessed in field experiments in Switzer land, during 1997. In a first experiment, eggs and larvae were released on 3-year old apple trees infested with five aphids at four different predator -prey ratios (0:5, 1:5, 1:1, 5:1). In a second experiment, eggs and larvae were released at a predator-prey ratio of 5:1 on branches of apple trees na turally infested with aphids. In both experiments, the interaction with ant s was taken into account and the releases were done at two different times in spring. The results showed that an augmentative release of larvae signif icantly prevented the build-up of colonies of D. plantaginea. Significant r eductions in aphid numbers were recorded at the two highest predator-prey r atios, 1:1 and 5:1. Larvae were efficient just before flowering of apple tr ees at a time when growers normally have to spray their trees. On trees whe re ants were present the larvae of A. bipunctata were significantly less ef ficient. Effects of eggs of A. bipunctata, however, were less reliable. At the first date of release (5 April), they did not hatch, probably as a cons equence of bad weather conditions.