Pest Information: Whiteflies
Whiteflies are one of the most important pests in
greenhouses, nursery and ornamental settings. Several different species
of whiteflies occur in greenhouses and on ornamentals and one or more
of them attacks a variety of hosts including geraniums, fuchsia,
hibiscus, and poinsettia. Most whiteflies are similar in appearance.
The adults are small, snow white colored and four winged. Their larvae
are very small, oval flat and pale-green to yellow, and are found on
the underside of the leaf. The larvae suck the sap from the plant.
Infested foliage can be noticed as it lacks vigor, then wilts, turns
yellow, and dies. The leaves are covered with a coating of honeydew, a
sweet, sticky material on which a sooty-colored fungus often grows,
completely covering the foliage.
The female whitefly deposits 30 - 500 small,
cigar-shaped, yellowish eggs during her lifetime. These are attached to
the undersides of the leaves by a short stalk and are often laid in a
small ring, as the female circles about with her mouth parts inserted
in the leaf. Egg hatch is affected by temperature, but generally occurs
in 7 - 10 days. Upon hatching the first instar nymphs move a short
distance then settle on the leaf to feed, remaining in this position
until they become adults. They suck the sap from the phloem tissue of
the leaf, feeding greedily on the plant juices for about 3 to 5 weeks,
depending on temperature and species. In this space of time they pass
through four instars, or immature stages. Greenhouse whitefly nymphs
have fine, white, waxy threads, radiating from their greenish bodies.
Silverleaf whitefly nymphs are flattened or convex, without these
fringes of threadlike hair.
The adult whitefly is very active, four-winged and
has the appearance of having been thoroughly dusted with very fine
white material. The hind wings are almost equal in size to the front
wings, providing an easy character to differentiate them from aphids,
psyllids, and similar insects. Both females and males can fly, and they
feed, like the nymphs, on the undersides of the leaves. Under most
conditions generations overlap and all stages of the insect may be
found infesting plants at any time.
There are many whiteflies that can attack greenhouse and nursery crops including:
Greenhouse Whitefly (Trialeurode vaporariorum)
Sweet potato Whitefly (Bemisia tabaci)
Silverleaf whitefly (Bemesia argentifolii)
Wooly Whitefly (Aleurothrixus floccosus)