Whiteflies are actually more closely related to aphids, scales and mealybugs. They are not flies. Whitefly populations are increase rapidly in the warm, long days of summer, and they will be around until the weather cools and the rains of late fall begin. The most common whitefly on the Central Coast is the greenhouse whitefly. The host range of this insect is large and it finds avocado, beans, mums, hibiscus, lantana, morning glory, squashes, peppers, strawberry, tomato, peas and many, many other plants to its liking, The female lays her eggs on the underside of leaves. The eggs hatch to produce a nymph, which very quickly settles down and “inserts” its hypodermic needle mouthparts into the leaf to begin sucking out plant nutrients. While feeding, the nymph will excrete honeydew, which makes plant surfaces sticky and also provides a substrate for the growth of sooty mold fungi, which coats leaves, stems, and fruit with a black coating.
During warm weather whiteflies can mature from egg to egg laying adult in 15 to 20 days. There are several ways to manage whiteflies. For light infestations, washing the infested plants down with a stream of water is helpful. The adults are very weak fliers, so if you can knock them off the plant and get them stuck in the mud under the plant, they will die. If you know a pest management landscape maintenance person, he can get and release whitefly parasites that can help bring a persistent whitefly population under control. The parasites should be released periodically through the spring and summer months to maintain effective whitefly suppression. Finally, there are several insecticides, which can be used to suppress whiteflies. For ornamental plants, there is now a systemic product available to the home gardener.