aphids (greenfly & blackfly)

Damage:
Aphids feed on plant sap and excrete a sticky "honeydew" on which growths such as sooty mould often develop

They normally feed at shoot tips, which restricts and deforms plant growth.

Sooty mould reduces the amount of light reaching the plant leading to leaf yellowing and defoliation.

Life Cycle:
Any aphid about to give birth is effectively three generations in one! Not only is the adult aphid about to give birth to immature aphids, but these already have the next generation of young developing inside them.

Young are produced at a rate of about 3 to 6 per day for several weeks.
When aphid colonies become dense some wingless aphids will move off to find new places to produce their young.

The aphid colony will also start to produce a much higher proportion of winged aphids which are capable of finding new breeding sites further a field.

Aphids can generally over-winter in a greenhouse on weeds or crops. 

Biological Control of Aphids.

Aphids can be controlled biologically in greenhouses or conservatories by using their natural enemies Aphidius or Aphidoletes or a combination of both.
A Ladybird, Lacewing, Garden Predators Box can help to encourage beneficial insects to stay in your garden to help control Aphids outside.