Whitefly (Trialeurodes vaporariorum) is one of the most common and troublesome of greenhouse pests. The adults are small white moth-like insects that occur in large numbers on the undersides of leaves. Their whitish-green nymphs and pupae resemble scales and, like the adults, feed by sucking sap from the underside of leaves. Whiteflies produce few initial symptoms allowing numbers to build until plants lose vigour, leaves droop, turn yellow, wilt, and sometimes die. Leaves become glazed with sticky honeydew. Eggs are laid in circles on underside of leaves near the tops of plants. Whiteflies are vectors of viral diseases.
The immature stages are relatively immune to insecticides but the adults can be killed by spraying with insecticidal soap. If the plant have become heavily infested control measures may have to be taken every 3-4 days in order to kill the adults as they develop. Adults are attracked to yellow objects, so use sticky traps initially. Severely infested plants should be rogued. Avoid aubergine, sweetpotato, tobacco and cotton crops.
Control with soft soap sprayed onto underside of leaves, then introduce the parasitic wasp Encarsia. Neem mimics whitefly growth hormones and effectively kills whitefly nymphs.