Aphid Parasite
The Aphid Parasite (Aphidius colemani) is a small wasp about the size of a gnat (2-3 mm long), which can not sting humans. They are found in nature, but are also sold for release in gardens and greenhouses in order to control aphid populations. They prefer temperatures between 10-25°C and relative humidity between 70-80%. The Aphid Parasite is used in the control of green peach and melon aphids.
The female wasp curls up her abdomen, stabs an aphid, and lays 1 egg inside the body. Each female may lay in excess of 100 eggs.
The wasp larva will hatch, and feed on the aphid, which kills it, then it will spin a cocoon while still in the aphid's body. When the larva in the cocoon matures into a wasp, it emerges out the back of the aphid body, which by now has swollen to look like a hard, light whitish-brown shell.
In the home garden, the wasps should be naturally occurring where they are suited. But providing a habitat, and not using pesticides, they should stay and parasitize aphids.
In commercial greenhouses, as a preventative measure, one wasp can be released for every 2 square metres weekly for 3 consecutive weeks. If there is an existing aphid infestation, 2 wasps per square metre should be released each week, for 3 consecutive weeks.