The whitefly begins its life in an egg, usually laid on the underside of a leaf on its host plant. Some species do not lay their eggs randomly. For instance, the Giant Whitefly tends to lay its eggs in some sort of spiral pattern. After hatching the juvenile whitefly goes through 4 larval instars or stages. The first instar, called a crawler, is mobile. The crawler locates a suitable minor leaf vein, taps it and feeds on the plant's phloem fluids. After the crawler molts, the larval whitefly can no longer move about, but continues to feed on phloem fluids. The second and third instar larvae tend to be flattened and oval-shaped. Those of the Giant Whitefly are green to greenish-yellow, blending well with the leaf coloration, and are clustered within the egg spiral. Whiteflies produce honeydew as a waste product. Since the larvae can't move, the accumulation of large amounts of sticky honeydew in the local area could have serious consequences. The whitefly avoids this problem by storing the honeydew temporarily in a depression on the outside of its cuticle. This honeydew is periodically ejected using a specially structured catapult. The fourth instar, the most distinctive, is often used for identification purposes. This stage of the Giant Whitefly is very impressive. The larva is covered with white wax and very long wax filaments. Leaves supporting fourth instar larvae appear to be growing fine whitish beards. The adult insect emerges from the molt ending the fourth stage. Adult whiteflies also feed on phloem fluids. Since adults are not strong flyers, they tend to stay near the vegetation. Adults are easily dispersed by the wind.
In California, some whitefly species have gained notoriety because of the extensive damage they have caused to agricultural crops. In addition to debilitating plants and reducing crop yields, the adults of some species can transmit plant diseases. The honeydew produced can support a black mold fungus. Whiteflies have many natural enemies including a number of beetles (some deliberately introduced) and parasitic wasps.
At Chula Vista, I have found the occasional whitefly on Tree Tobacco leaves. With more local development, I expect to find the Giant Whitefly eventually. Giant Whiteflies lived on cocklebur and non-native acacia trees near the entrance to the Torrey Pines extension. Egg spirals were found on the Tree Tobacco and Castor Bean leaves. I have found Giant Whiteflies on hibiscus and people have reported them on tomatoes, peppers and begonias. The Giant Whitefly is an interesting but, for most people, probably an unwelcome addition to the insect fauna of San Diego County.
Ron Lyons (volunteer 1990-1999)