Whiteflies

(View illustrations to identify whiteflies)

Whiteflies (family Aleyrodidae) are named for the appearance of the small (0.12 inch, 3 mm or less), pale, powdery adults. Females lay tiny oblong eggs on foliage. The first-instars nymphs that hatch from eggs are initially mobile and called crawlers. Crawlers soon settle to feed and lose their legs. The subsequent three nymphal stages and pupal stage are inactive. Nymphs are generally flattened and oval and may resemble certain soft scales. Whiteflies are identified to species primarily by the color, shape, and waxiness of the fourth-instar nymph or pupa. In approximate order of their abundance, the species in California avocado are redbanded whitefly, nesting whitefly, greenhouse whitefly, mulberry whitefly, and giant whitefly.

For most whiteflies all life stages can be present at any time, with several generations each year. For example, one greenhouse whitefly generation from egg to adult takes about 4 to 6 weeks depending on temperature. However, in California, redbanded whitefly has just one generation per year.

Whiteflies suck phloem sap. They excrete honeydew, which collects dust and supports growth of blackish sooty mold fungi that can foul fruit. Honeydew attracts ants, which interfere with the biological control of whiteflies and many other pests. Giant whitefly, greenhouse whitefly, and mulberry whitefly each have hosts in over a dozen plant families. Nesting whitefly prefers citrus, but also infests avocado and some ornamental broadleaf evergreens. Redbanded whitefly has been found only on avocado in California. Whiteflies have many natural enemies, of which parasitic wasps are especially important, and consequently usually are under very good biological control.

• Conserve natural enemies, especially parasitic wasps, which provide partial to complete biological control of most whitefly species unless disturbed by ants, dust, or insecticides.
• Control dust by watering or paving main orchard roads. Use a water truck or trailer to wet unpaved roads, especially during summer months when dust moving up into the tree canopies can especially disrupt natural enemies.
• Where ants are common on trees, consider applying barriers or insecticide baits to control them. Apply selective pesticides for other pests, such as Bacillus thuringiensis (Bt) for caterpillars, to conserve natural enemies.

No pesticide applications are recommended for whiteflies in avocado. Chemical treatment of whiteflies often is not effective; temporary suppression may be achieved only to be followed by a resurgence of the pest, especially after applying certain broad-spectrum insecticides. Have any unfamiliar whiteflies identified by an expert. New species periodically are introduced into California.

Parasitic wasps are the most important natural enemies. These include many Cales, Encarsia, and Eretmocerus spp. (family Aphelinidae). Parasitized immature whiteflies often change color and have round exit holes through which the adult parasite emerged.

Predators of whitefly nymphs include bigeyed bugs (Geocoris spp.), green lacewings (Chrysoperla spp.), lady beetles (Delphastus spp.), and pirate bugs (Orius spp.). Spiders feed on adult whiteflies.

• Avoid moving uncertified or infested plant material from one orchard to another to minimize pest spread.
• Make sure bins are clean when transporting bins from giant whitefly infested areas to clean groves.
• Do not bring plant materials into California from other states or out of the country because they may be infested.
• Control dust.

Use biological and cultural controls in an organically certified crop.