What is a biological control of greenhouse whiteflies?

The parasitic wasp Encarsia formosa is an effective biological control of greenhouse whiteflies [Trialeurodes vaporariorum]. But temperatures mustn't be allowed to fall below 24 degrees Centrigrade/75 degrees Fahrenheit. Otherwise, the biological control dies before the pest because the lower temperatures keep the wasp from reproducing.

Answer

The above answer is correct. If you are unable to hold the required temperature try

using pots of Tagetes dotted around. They don't kill the whitefly but the whitefly dislike the smell and go elsewhere.