Natural enemies (Rosy apple aphid)

A wide range of predators and parasites are natural enemies of rosy apple aphid. However, when weather and tree growth conditions are favourable in spring, population increase by the aphid is too rapid for natural enemies to prevent population increase and damage. Natural enemies have a greater effect when plant growth slows or ceases in summer.

Predation of aphids and their eggs in the autumn may be more significant as the number of overwintering eggs may be substantially reduced resulting in a smaller number of colonies developing in spring. This may be the reason why more colonies often develop in spring in insecticide treated than untreated orchards.

Some ant species attend aphid colonies, protecting them from generalist predators so that they can feed on the honeydew produced by the aphids. The common black ant (Lasius niger) will even move aphids to fresh leaves to start new colonies. Research by Niab at East Malling has shown that sugar-based pellets can disrupt ants, preventing them from attending the aphid colonies, exposing the aphids to predation and successfully reducing aphid populations. 

British Apples and Pears Ltd funded a project where Niab tested six different sugar pellet formulations provided by Russell IPM both for their suitability in field experiments and to test their ability to disrupt ant tending of rosy apple aphid. Two pellet formulations were attractive to ants on the orchard floor, but further work is required to determine the optimum pellet placement. The pellets were also found to be attractive to foxes so further work is required to develop pellets that are attractive to ants but distasteful to mammal predators.

Predatory insects and spiders

• A wide range of predatory insects prey on rosy apple aphid including earwigs, predatory anthocorid and mirid bugs, lacewing and hoverfly larvae, predatory midge larvae, ladybird adults and larvae and spiders.

Parasitic wasps

• Ephedus persicae is the most important species in spring but contributes little to natural control of the aphid. Ant attendance and hyperparasitism decrease the impact of parasitic wasps.

Entomopathogens

• Outbreaks of fungal pathogens (Entomophthora sp) have been reported from rosy apple aphid colonies occasionally causing population crashes but their importance has not been investigated adequately.