CAUTION: This information was developed for North Carolina and may not apply to other areas.
Citrus Whitefly, Dialeurodes citri, Aleyrodidae: HOMOPTERA
The most common insect complaint on gardenia in North Carolina is citrus whitefly. Small adult citrus whiteflies damage their host plants directly by ovipositing and feeding. Immature citrus whiteflies suck sap from the leaves. Also, the honeydew excreted by the feeding whiteflies provides an excellent medium for the sooty mold fungus Capnodium citri. This fungus coats the leaves and stems of infested plants, making them look unhealthy, and may reduce photosynthesis. Heavily infested gardenias with substantial sooty mold may drop their leaves prematurely. The adult whiteflies themselves are often not seen, but the scale insect-like pupal stage may be more evident.
The citrus whitefly was introduced from Asia. Until the advent of synthetic organic pesticides, this pest caused an estimated loss of 45 to 50 percent of the citrus crops in Florida and the Gulf states. Among many other host plants, gardenias seem to be highly susceptible. In fact, one of the infestations eradicated in California (at considerable expense) originated from a gardenia that had been smuggled into the state. The citrus whitefly has been reported on at least 38 genera of evergreen and deciduous plants. Preferred host plants include citrus, chinaberry, gardenia, privet, prickly ash, pomegranate, and Japanese persimmon.
The adult is a small, moth-like insect, orange but covered by a snow-white waxy bloom.
Eggs are almost microscopic and pale yellow-green in color. Crawlers are tiny and pale green, have six legs, two antennae, and two red eyespots. The flattened nymph is pale green and scalelike.
Each female citrus whitefly may lay up to 125 eggs, which are partially inserted into the lower leaf surface. In heavy infestations, eggs may be so numerous that leaves are malformed and growth is impaired. The eggs hatch in 6 to 21 days, and tiny, pale-green crawlers move about the plant seeking a place to feed. When they insert their long, threadlike mouthparts into the lower leaf surface, they become immobile. After the first molt, legs and antennae are lost. After two additional molts, the pupae form. The adults finally emerge from T-shaped splits in the pupal skins. There are three broods each season in Alabama and Florida. Summer broods require about 2 months for development. The last brood overwinters in the immature stage.
At least three species of lady beetles are known to feed on citrus whitefly crawlers and nymphs, but they are seldom numerous enough to effect control by themselves. A tiny parasitoid wasp, Encarsia lahorensis, is a valuable beneficial and has been introduced into several states, including NC, to help reduce citrus whiteflies. Lacewing larvae are also known to eat whiteflies.
Insecticides should be applied in late spring before the emergence of first-generation adult whiteflies. The spray should be directed to the undersides of the leaves. Horticultural oils are very effective when timed correctly and with several applications. They do less harm to the beneficials. In the past, products such as orthene or malathion were recommended. Some of the pyrethroids such as Talstar, Tame, or some of the homeowner tree and shrub products containing cyfluthrin, bifenthrin, and resmethrin, are highly effective. Some of the systemic insecticides containing imidacloprid (Merit and Bayer Advanced) or dinotefuran (Safari and GreenLight Tree and Shrub with Safari) are highly effective when used properly.
Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical.
For assistance, contact your county North Carolina Cooperative Extension Service agent.
Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.