Aphid control

Most crops can be attacked by aphids. Damage is caused in three ways: sucking plant sap when feeding so reducing plant vigour, excretion of honeydew leading to sooty mould and some species can transmit plant viruses leading to distortion and disfigured plant growth. 
Biological control with parasitoids, predators and fungal pathogens is available depending on crop and environmental conditions. There are a large number of aphid species and identification can be important when parasitic wasps are to be used. Depending on the aphid species there can be alternate plant hosts. Winged forms develop under conditions of high density to migrate to alternate hosts. Resistance to some insecticides is a serious issue with some species. 

Parasitic Wasps

The adult wasp inserts its egg into the aphid, a parasite larva develops killing the aphid, producing a characteristic golden-brown papery 'mummy' with Aphidius and Praon species, and black 'mummy' with Aphelinus species. Aphids parasitised with Ephedrus hide to die. 
An adult parasitic wasp later emerges through a round hole on the mummified aphid. The adult wasps also feed as a predator on aphids, killing one or more each day. 

Species of parasitic wasp available:

Aphidius colemani  Particularly effective against round-bodied aphid species such as Myzus persicae (peach-potato aphid) and Aphis gossypii (melon cotton aphid). They are not effective against Aulacorthum or Macrosiphum species. It can control large populations of aphids, but will take time to achieve this and may leave many parasitised 'mummy' bodies on plants.
Aphelinus abdominalis  Controls a wide range of aphid species including Macrosiphum euphorbiae (potato aphid) and Aulacorthum solani (glasshouse potato aphid). It has a very long life span. 
Aphidius ervi
Specifically for the larger elliptical shaped species including Macrosiphum euphorbiae (potato aphid) and
Aulacorthum solani (glasshouse potato aphid). Several other aphid species such as the pea aphid are also parasitised. 
Aphidius matricariae  Has a slightly different host range to A. colemani and includes Ovatus crataegarius (mint aphid). 
Ephedrus cerasicola (Mixture Only) Has a long life cycle and high rate of egg-laying capacity. Effective on a wide range of aphid species. 
Praon volucre (Mixtures Only) Controls a wide range of aphid species including a number not controlled by other available aphid parasites and has a long life cycle.  

Formulations

Introduce at the rate of one wasp or mummy per 2m2 per week for Aphidius colemani, Aphidius ervi, Aphidius matricarae and Aphelinus abdominalis. For Veg mix (ACE)and CE mix a rate of one wasp per m2, Aphiline Berry, flower and strawberry mix are supplied in a release pack to treat 200m2.

The mixtures reduce the need for accurate pest species identification and are suitable preventative use against a range of aphid species. Particularly in mixed cropping situations. 

Recommended biological controls for aphid