No, the giant whitefly doesn't block out the sun with huge wings. However, it is a giant by whitefly standards measuring in at 3/16 inch long.  It was first discovered in southern California in the early 1990s and is now found in many areas of California, including Napa County.

Giant whitefly can severely infest many ornamental plants. A recent call to the UC Master Gardeners of Napa County help desk has documented two serious infestations of giant whitefly, one on an unspecified tree and one on an ornamental plant. 

Some plants are more affected by the giant whitefly than others. They include begonia, hibiscus, giant bird of paradise, mulberry and various vegetables. Certain varieties of citrus and avocado are also affected.

IDENTIFICATION AND LIFE CYCLE Whiteflies go through three developmental stages: egg, a progression of immature stages called nymphs, and the adult stage. This species can also be identified by the spirals of wax that are deposited by adults as they walk on leaves. Eggs are laid among the wax deposits. After hatching, the nymphs produce long hairlike filaments of wax up to 2 inches long giving a bearded appearance to affected leaves. After adults emerge, the majority will remain on the same plant to feed and lay eggs.

PEST DAMAGE Whiteflies can damage plants directly by their feeding. Both nymphal and adult whiteflies feed by inserting their needlelike mouthparts into the vascular tissue or phloem of the leaves and suck out the plant sap. The plant can suffer from lack of water and nutrients, resulting in a weakened plant, but rarely in plant death.

Sooty mold: During feeding, whiteflies excrete a sticky, sugary solution called honeydew that accumulates on leaves and fosters the growth of the black sooty mold fungus. This sooty mold is not only unattractive, it also reduces the photosynthetic (food-producing) abilities of the leaves.

MANAGEMENT Try to manage giant whiteflies in your landscape with an integrated program that includes removal of infested leaves and, if necessary, washing whiteflies off leaves with water. Insecticides are not generally recommended. A forceful stream of water (syringing) directed at colonies can be just as effective as insecticide sprays.

Leaf or Plant Removal: The tendency of giant whitefly adults to remain on the plant where they developed leads to a strongly clustered distribution. Leaf removal is most effective when populations are restricted to a few plants or leaves. Place infested material in plastic bags, seal, and remove the bags from the property. Leaf removal will work better on some plants than others. On more preferred host plants, such as red hibiscus, control will require early detection, rigorous leaf removal, and syringing with water. In high traffic or visible areas that are near walkways, doors, or windows, removing or replacing infested plants may be your only option.

Syringing: With high whitefly populations, syringing (spraying with water) is recommended at least once a week. As populations decrease, intervals can be lengthened to once every 2 or 3 weeks. An additional advantage of syringing is improved plant appearance.

Biological Control Native insect predators such as green lacewings (Chrysopa and Chrysoperla spp.), syrphid fly larvae (also called hover flies), and lady beetle adults and larvae attack giant whitefly in California but do not provide adequate biological control. Parasitic wasps are often found parasitizing giant whitefly leaves. These tiny, stingless, parasitic wasps lay their eggs inside the whitefly larvae. When the wasp eggs hatch, their larvae feed on the giant whitefly larvae. The wasp then pupates and emerges, leaving behind either a hollow shell. While these parasites don't completely eradicate all of the whiteflies, they can dramatically reduce their numbers.

Natural enemies: The whitefly parasites mentioned above are being released by University of California and California state scientists. It is hoped that these parasites will permanently establish and distribute themselves throughout infested areas. Release off commercially available natural enemies by home gardeners should not be necessary..

Chemical Control Although some insecticides are registered to control giant whitefly either by foliar or soil application, their use is not recommended if parasites are present in the area. To determine if parasitic wasps are present, use a hand lens to examine several leaves containing whitefly nymphs. Look for a dark discoloration of the nymph or the tiny holes that parasites make when they emerge from the dead larva. If there is evidence of parasites, don't use insecticide treatments.

If you do choose to use insecticides, select least-toxic products such as insecticidal soaps or oils. Remember to follow label directions and spray undersides of leaves where whitefly colonies are found. WARNING ON THE USE OF CHEMICALS

___________________________

All photos courtesy of Kenneth Fuller except for photo showing eggs, pupae & nymphs from UC Statewide IPM 

UC Master Gardeners of Napa County provide free home gardening advice. Visit, call or complete the 

Plant Problem Diagnosis Sheet  for assistance. 

Monday, Wednesday and Friday, 9 a.m. to 12 p.m.
UC Cooperative Extension 
1710 Soscol Avenue, Suite 4, Napa
(707) 253-4143

http://ucanr.edu/sites/ucmgnapa/

REFERENCES: UC IPM  

http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7400.html

Whitefly ID : http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7401.html

Dreistadt, S. H., J. K. Clark, and M. L. Flint. 2001.

Integrated Pest Management for Floriculture and Nurseries. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 3402.

PUBLICATION INFORMATION: Pest Notes: Giant Whitefly: Integrated Pest Management for Floriculture and Nurseries. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 3402.