|Crop Knowledge Master|
Aleurodicus dispersus (Russell)
Jayma L. Martin Kessing, Educational Specialist
Ronald F.L. Mau, Extension Entomologist
Department of Entomology
The spiraling whitefly has been recorded on 38 genera of plants belonging to 27 plant families and more than 100 species (Waterhouse and Norris, 1989). It is common to find this pest attacking many vegetable, ornamental, fruit and shade tree crops in Hawaii. Specific plants that are attacked include annona (cherimoya, atemoya, sugarapple), avocado, banana, bird-of-paradise, breadfruit, citrus, coconut, eggplant, guava, kamani, Indian banyan, macadamia, mango, palm, paperbark, papaya, pepper, pikake, plumeria, poinsettia, rose, sea grape, ti and tropical almond.
The spiraling whitefly is a native to Central America and the Caribbean region. In the Americas it has been reported in the Bahamas, Barbados, Brazil, Canary Islands, Costa Rica, Cuba, Dominica, Ecuador, Haiti, Martinique, Peru, Philippines, Panama and southern Florida. In the Pacific it is present in American Samoa, Cook Islands, Fiji, Hawaii, Kiribati, Majuro, Mariana Islands, Nauru, Palau, Papua New Guinea, Pohnpei, Tokelau, Tonga and Western Samoa (Waterhouse and Norris, 1989). This whitefly was first reported in Hawaii in 1978 on the island of Oahu and was reported all major islands by 1981. This whitefly is most abundant in coastal areas and elevations below 1000 feet.
Three types of damage may be caused by the spiraling whitefly: 1) direct damage, 2) indirect damage and 3) virus transmission (Berlinger, 1986).
Direct feeding damage is caused by the piercing and sucking of sap from foliage by immature and adult stages of whiteflies. The majority of feeding damage is done by the first three nymphal stages. This feeding causes premature dropping of leaves. Direct feeding damage, even during heavy infestations, is usually insufficient to kill plants (Waterhouse and Norris, 1989).
Indirect damage is due to the accumulation of honeydew and white, waxy flocculent material produced by the whiteflies. Like other soft bodied insects such as aphids, leafhoppers, mealybugs and scales, whiteflies produce honeydew. This sweet and watery excrement is fed on by bees, wasps, ants and other insects which, in turn, may tend and offer protection to the whiteflies. The honeydew also serves as a substrate on which sooty mold grows. Sooty mold blackens the leaf, decreases photosynthesis activity, decreases vigor and often causes disfigurement of the host and lessens the market value of the plant or makes it unmarketable (Berlinger, 1986). The flocculent material produced by the nymphs is scattered by the wind and creates an unsightly nuisance (Waterhouse and Norris, 1989).
The third type of damage is a result of the ability of this insect to act as a plant disease vector. A small population of whiteflies is sufficient to cause considerable damage (Cohen and Berlinger, 1986). Plant viruses transmitted by whiteflies cause over 40 diseases of vegetable and fiber crops worldwide. Among the 1,100 recognized species of whiteflies in the world, only three are recognized as vectors of plant viruses. In the past decade, whitefly-transmitted plant viruses have increased in prevalence and distribution. The recent impact has been devastating with yield losses ranging from 20 to 100 percent, depending upon the crop, season, and prevalence of the whitefly among other factors.
A few to several dozen tiny, elliptical, smooth surfaced, yellow to tan eggs, along with numerous tiny waxy secretions, are deposited on the surface of a leaf, usually on the underside, in irregular, waxy lines, typically forming a somewhat spiraling pattern. The spiraling of waxy material is the feature from which this whitefly derives its common name, the spiraling whitefly (Waterhouse and Norris, 1989). The eggs are usually laid on the underside of the leaf at right angles to the leaf veins. Eggs hatch in 9 to 11 days under glasshouse conditions with temperatures ranging from 68û to 102.2ûF (20û to 39ûC) (Waterhouse and Norris, 1989).
There are four immature stages, the first three are referred to as larvae and are continuous feeders (Waterhouse and Norris, 1989). The first larval stage, sometimes called a "crawler", is the only immature stage with functional legs and distinct antennae. Subsequently, the first stage is the only stage capable of active movement. All other immature stages are sedentary.
Once the crawlers settle, they develop a characteristic row of mid-back waxy tufts on the anterior of their body. The waxy tufts continue to grow as more material is secreted. During the third larval stage glass-like rods of wax appear along the sides of the body. These glass-like rods are extruded through special pores on the insects body and may be as much as 1/3 inch (8 mm) long, although most are shorter because of fragmentation (Waterhouse and Norris, 1989).
The first larval stage last for 6 to 7 days, the second 4 to 5 days and the third 5 to 7 days under glasshouse conditions with temperatures ranging from 68û to 102.2ûF (20û to 39ûC) (Waterhouse and Norris, 1989).
The final and fourth immature stage is considered the pupa of this species. This stage feeds during the earlier phases then stops feeding and undergoes internal tissue reorganization before molting into the adult (Waterhouse and Norris, 1989). This stage serves as the basis for most of the taxonomic characterizations and must be observed under the microscope for those characteristics.
The mature pupae bears a copious amount of a white cottony secretion extending upward and outward from the back. Some of the secretion is fluffy and some waxy and in ribbons as long as, or longer than, the width of body. Pupae are colorless or yellowish, nearly oval, flat and approximately 1/25 inch (1 mm) long and 3/50 inch (0.75 mm) wide.
The pupal stage lasts for 10 to 11 days with temperatures ranging from 68û to 102.2ûF (20û to 39ûC) under glasshouse conditions (Waterhouse and Norris, 1989).
The adults are similar in appearance to those of many other species of whiteflies. They are white and quite small 1/12-1/8 inch (2-3 mm) in length and coated with a fine dust-like waxy secretion. They somewhat resemble tiny moths, and both sexes are winged. The eyes of this whitefly are dark reddish-brown. Wings are transparent after emergence from the pupal casing, but develop a white powder covering after a few hours (Waterhouse and Norris, 1989). The forewings each have two characteristic black spots (Paulson and Kumashiro, 1985). Adults live up to 39 days under laboratory conditions (Waterhouse and Norris, 1989).
Females begin laying eggs within a day of emergence and continue to lay eggs throughout her lifetime. Unmated females produce only male progeny while mated females produce both sexes. In an experimental study, 20 pairs of whiteflies produced 1549 progeny in 37 days (Waterhouse and Norris, 1989).
Only the adult stage disperses beyond the leaf on which the egg is laid. They are most active during the morning hours (Waterhouse and Norris, 1989). Mating occurs during in the afternoon (Waterhouse and Norris, 1989).
Populations of this insect thrive in warm, dry weather. Heavy rains and cool temperatures may result in a temporary reduction of spiraling whitefly populations (Waterhouse and Norris, 1989). Mortality increases significantly between temperatures of 104û and 113û F (40û and 45ûC) for immature stages and between 95û and 104û F (35û and 40û C) for adults (Cherry, 1979). The same study by Cherry (1979) showed mortality at temperatures below 50û F (10û C).
After first being reported in Hawaii in 1978, the spiraling whitefly was considered a major economic pest by 1979 and extensive searches were conducted for natural enemies to be introduced to control whitefly populations. Five natural enemies were introduced into Hawaii from the Caribbean to control the spiraling whitefly. One of the three coccinellid beetles, Nephaspis oculatus (previously N. amnicola), has proved effective with high population densities of whitefly (Kumashiro et al., 1983). Although the majority of the prey are nymphs, this beetle feeds on all stages of whiteflies (Yoshida and Mau, 1985). The two parasitic wasps, Encarsia haitiensis (Dozier) and Encarsia sp. were the most effective, especially against low populations densities of whitefly (Kumashiro et al., 1983). Encarsia haitiensis is believed to be host specific (Waterhouse and Norris, 1989). In 1980 to 1981 peak populations of this whitefly were reduced by 79% at lower elevations and 98.8% in higher elevations (Kumashiro et al., 1983) and by July 1981, the spiraling whitefly was considered under control. Predators introduced to control other pests may also contribute in the reduction of spiraling whitefly populations, especially the coccinellid beetles Delphastus (previously Nephaspis) pusillus and N. bicolor, which also attack other whitefly species as well as many scales, mealybugs, and aphids.
Contact and systemic insecticides recommended for other pests on the same plant hosts may temporarily reduce spiraling whitefly populations (Waterhouse and Norris, 1989). Dilute aqueous solutions of detergents and soaps have been reported as helpful.
Temporary control measures for the homeowner suggested by the Hawaii Department of Agriculture (Anonymous, 1980) are listed below.
* Use a mild solution of soap, mixing an inexpensive liquid dish washing detergent at a rate of no more than 1 tablespoon per gallon of water, and thoroughly spray the underside of infested leaves. Sensitive plants such as ferns may suffer a "burning" effect so less detergent (1 teaspoon) per gallon of water should be sprayed on these plants.
* Apply a strong stream of water onto the underside of infested leaves as often as possible without wasting water. This can be done during normal watering of plants.
* Judicious pruning of leafy plants. Thin out excess branches to give the plant an "umbrella" appearance with scattered openings in the canopy to allow sun, wind, and rain to penetrate. This will reduce the surface area of foliage that needs to be sprayed and eliminate shelter for the spiraling whitefly.
* Heavy mulch of sawdust, wood shavings, bark and other organic material around the base of the plants out to the drip line (circumference of root spread indicated by extremities of branches) of plants to conserve soil moisture during hot, dry or windy weather. The spiraling whitefly removes plant fluids and increases moisture loss over the amount due to normal transpiration. Therefore, the plants will require additional soil moisture to prevent wilting.
* Periodic fertilization of plants to improve plant vigor. Healthy plants will be better able to withstand spiraling whitefly infestations.
Anonymous. 1981. Hawaii Pest Report. 1(5): 1-10. Hawaii Department of Agriculture Plant Pest Control Branch.
Anonymous. 1980. Bio-Control of the Spiraling Whitefly. Biological Control Section Plant Pest Control Branch Department of Agriculture. 2 page pamphlet.
Berlinger, M.J. 1986. Host Plant Resistance to Bemisia tabaci. Agric. Ecosystems Environ. 17: 69-82.
Cherry, R,H, 1979. Temperature Tolerance of Three Whitefly Species Found in Florida. Environ. Entomol. 8: 1150-1152.
Cohen, S. and M.J. Berlinger. 1986. Transmission and Cultural Control of Whitefly-borne Viruses. Agric. Ecosystems Environ. 17: 89-97.
Kumashiro, B.R., P.Y. Lai, G.Y. Funasaki and K.K. Teramoto. 1983. Efficacy of Nephaspis amnicola and Encarsia haitiensis in Controlling Aleurodicus dispersus in Hawaii. Proc. Hawaiian Entomol. Soc. 24 (2 & 3): 261-269.
Paulson, G.S. and B.R. Kumashiro. 1985. Hawaiian Aleyrodidae. Proc. Hawaiian. Entomol. Soc. 25: 103-124.
Russell, L.M. 1965. A New Species of Aleurodicus Douglas and Two Close Relatives (Homoptera: Aleyrodidae). Florida Entomologist. 48(1): 47-55.
Waterhouse, D.F. and K.R. Norris. 1989. Aleurodicus dispersus spiraling whitefly. pp. 12-23. In: Biological Control Pacific Prospects - Supplement 1. Australian Center for International Agriculture Research, Canberra.
Weems, H.V. 1971. Aleurodicus dispersus Russell (Homoptera: Aleyrodidae), a Possible Vector of the Lethal Yellowing Disease of Coconut Palms. Entomology Circular No. 111. Florida Department of Agriculture and Consumer Services Division of Plant Industry.
Yoshida, H.A. and R.F.L. Mau. 1985. Life History and Feeding Behavior of Nephapis amnicola Wingo. Proc. Hawaiian Entomol. Soc. 25: 155-160.