Introduction
Whiteflies are very small insects that resemble tiny white moths. Whiteflies usually feed on the lower surface of their host plant leaves. Whiteflies differ from most insects in the way they mate (side by side) and that their eggs absorb water from the host leaf after the eggs are inserted into the lower surface. From the egg hatches a minute crawler stage that moves about the leaf until it inserts its microscopic, threadlike mouthparts to feed by sucking sap from the phloem. Adults and nymphs excrete honeydew, a sticky, viscous liquid in which dark sooty molds grow. Because many species of adult whiteflies are similar in appearance, entomologists use the last nymph stage for specific identification. In 1986, a whitefly very similar to the sweetpotato whitefly suddenly became a noticeable pest of poinsettias and commercial vegetables in Florida and California. This whitefly spread throughout the greenhouse industry in the United States in the next few years and is now the most frequently encountered whitefly pest of poinsettia and gerbera daisy. In 1994, Bellows and Perring described this whitefly as a new species, the silverleaf whitefly. The silverleaf whitefly causes the leaves of melons and stems of poinsettias to blanch noticeably when these whiteflies are abundant.
Key to the Most Common Whitefly Pests of Flowers and Foliage
- Pupal case (when viewed from the side) appears to be sitting on closely set posts of wax around the margin (Figure 172) - GO TO 2
Pupal case not sitting on posts of wax around the margin - GO TO 3 - Pupal case with a dark area along the back; adult with gray bands across the wings (Figure 173A, Figure 173B) - BANDEDWINGED WHITEFLY
Pupal case without a dark area along the back; adult with gray bands across the wings - GREENHOUSE WHITEFLY - Pupal case oval in shape, flat, without prominent caudal setae or caudal projections - CITRUS WHITEFLY
Pupal case with prominent caudal setae and caudal projections, plump, not flat - GO TO 4 - On azalea; pupal case without large dorsal setae, even if leaves are hairy - AZALEA WHITEFLY
Not on azalea; pupal case with large dorsal setae if leaves are hairy or without large setae if leaves are smooth - GO TO 5 - Thoracic tracheal folds relatively wide, wax at margin opening of tracheal folds relatively wide, the posterior wax slightly wider than the bases of the caudal setae, fourth anterior submarginal setae present; does not cause white stem symptom on poinsettia and silverleaf symptom on squash - SWEETPOTATO WHITEFLY
Thoracic tracheal folds relatively narrow, wax at margin opening of tracheal folds relatively narrow, the posterior wax no wider than the bases of the caudal setae, fourth anterior submarginal setae absent; causes white stem symptom on poinsettia and silverleaf symptom on squash - SILVERLEAF WHITEFLY
Figure 172. Pupal case (when viewed from the side) appears to be sitting on closely set posts of wax around the margin. Figure 173A. Pupal case with a dark area along the back. Figure 173B. Adult with gray bands across the wings.
Azalea Whitefly
Azalea whitefly (Figure 174), Pealius azaleae (Baker & Moles), Aleyrodidae, HOMOPTERA
DESCRIPTION
Adult
About 1.5 mm long, the adult is light yellow with the antennae and legs slightly lighter in color. Most of the body is covered with a white, waxy bloom. The eyes appear dark brown. As usual, the small moth-like adults fly about readily when infested plants are disturbed.
Egg
Azalea whitefly eggs are typical of other whiteflies in their irregular cylindrical shape that is somewhat pointed at one end and rounded at the other (base end). The base end has a tiny protuberance that is inserted into the leaf tissue. The eggs are 0.1 mm wide and 0.22 mm long. Color ranges from translucent creamy to dark gray tipped fading to paler gray at the base.
Nymph
The tiny nymphs are oval and light in color without any form of wax secretions.
Pupa
The pupal case is light yellow to an orange yellow in color, without any form of wax secretions and about 0.84 mm long. The marginal areas appear lighter in color than the mid-dorsal area. Some marginal indentations may be present when the pupal case has grown against the leaf hairs.
BIOLOGY
Distribution
This whitefly has been spread worldwide wherever azaleas grow. The first records in the United States were on plants received from Holland in 1910. Without a doubt azalea whiteflies occur in all southeastern states.
Host Plants
Azalea whiteflies infest all species of azaleas.
Damage
Infested plants become unthrifty, honeydew, and sooty mold detract from a healthy appearance. Unless controlled, large clouds of whiteflies take to the air when heavily infested plants are disturbed.
Life History
Little is known about this whitefly and its life cycle. Presumably it is very similar to other whitefly species. This whitefly overwinters as nymphs on azalea leaves. Adults emerge in early spring in North Carolina and lay eggs on the undersides of azalea leaves. The eggs are creamy and translucent, but turn gray as they age.
CONTROL
For specific chemical controls see your county Cooperative Extension publications on ornamental plant pests.
Figure 174. Azalea whitefly. A. Adult. B. Egg. C. Crawler. D. Pupa.
Bandedwinged Whitefly
Bandedwinged whitefly (Figure 175), Trialeurodes abutilonea (Haldeman), Aleyrodidae, HOMOPTERA
DESCRIPTION
Adult
Mature adult bandedwinged whiteflies have zig-zag bands across the front pair of wings. The hind pair of wings are unmarked. With the exception of the front banded wings this whitefly is very similar to greenhouse whitefly.
Egg
The eggs are about 0.12 mm long and 0.10 mm wide. Eggs are placed randomly or in circles on the leaf underside. Newly deposited eggs are pale yellow and turn pale pinkish just before hatching.
Nymph
Young nymphs are 0.37 mm long, and as nymphal stages progress become just over 1⁄2 mm long. They are translucent white, with a yellow spot on each side of the abdomen (Figure S). When the first instar nymph first settles down it begins to secrete a wax fringe that will become the side walls of the pupal case. As growth occurs the nymphal stages will secrete a marginal fringe of translucent setae, and the dorsal medial area of the integument becomes brown.
Pupa
The pupal case is just short of 1 mm long and 0.5 mm wide. The translucent marginal setae are of two lengths and the marginal palisade of wax rods is very distinct. The dorsal medial region is dark brown and uneven; the operculum is yellowish brown.
BIOLOGY
Distribution
Arizona, California, Colorado, District of Columbia, Florida, Georgia, Illinois, Indiana, Kansas, Kentucky, Louisiana, Maryland, Mississippi, Missouri, New Mexico, New York, North Carolina, Pennsylvania, South Carolina, Texas, Utah, and Virginia. In northern areas this whitefly probably survives the winter only in greenhouses, but in warmer areas lives outdoors on weed hosts.
Hosts
Originally described on Abutilon theophrasti, but is now considered a polyphagous feeder. Some common weed hosts are Ambrosia, Bidens, and Sida. Some important ornamental hosts include Euphorbia (poinsettia), Geranium, Hibiscus, and Petunia.
Damage
Infested plants become chlorotic and unthrifty from sap removal. Honeydew and sooty mold also detract from the aesthetics of the crop. Unless controlled, bandedwinged whitefly can be very damaging to a floriculture crop.
Life History
Bandedwinged whitefly reproduces much like the more studied greenhouse whitefly. Temperatures will greatly affect the time required for a complete generation. It is known that eggs will hatch in about 12 days at early April temperatures of a Kentucky greenhouse.
CONTROL
Controls after establishment of major infestations will be very similar for all whiteflies in a situation. Prevention of greenhouse invasion from out-of-doors in the fall will make controls much easier in late fall to early winter. Part of this prevention will have to involve sanitation with respect to weed hosts around the greenhouse, both indoors and outdoors. Also, the proper disposal of rejected and remaining infested plants in the fall is important.
Chemical controls will be similar regimens for nearly all whiteflies. Biological controls would perhaps be an important alternative on perimeter plants, and on plants that have a longer growing season. For specific chemical control recommendations, see your county Cooperative Extension publications ornamental plant pests.
Figure 175. Bandedwinged whitefly. A. Adult. B. Pupa.
Figure S. Bandedwinged whitefly nymph (left) and silverleaf whitefly nymph.
Citrus Whitefly
Citrus whitefly (Figure 176), Dialeurodes citri (Ashmead), Aleyrodidae, HOMOPTERA
DESCRIPTION
Adult
The adult is a tiny, moth-like, four-winged, mealy-white insect with a wing span of less than 4.3 mm. Most often they rest on the undersides of leaves and fly about when plants are disturbed.
Egg
The citrus whitefly lays yellow eggs with a nearly smooth surface. The eggs are about 0.25 mm long, elliptical, and most frequently laid on young tender leaves.
Nymphs
The first instar is the only mobile nymphal stage. After the first instar the nymphs are flattened, oval, and similar in appearance to soft scale insects. Nymphs are translucent, oval in outline, and very thin. The leaf color will show through the thin nymphal body, therefore nymphs are difficult to see.
Pupa
The pupal case is very similar to nymphs, but is slightly thickened and more opaque. The red eye spots of the adult are very prominent in developing pupal cases.
BIOLOGY
Distribution
Reported from Virginia southward and around to Texas, then westward to California.
Host Plants
The primary host plant is citrus of all types, but many ornamentals are also hosts. The most common are Allamanda, banana shrub, Boston ivy, chinaberry, English ivy, gardenia, lilac, pear, osage orange, and privet.
Damage
Direct damage is caused by the removal of sap. Indirect damage is caused by the excretion of copious amounts of honeydew where sooty molds grow. This black mold will contribute to poor aesthetics and perhaps interfere with photosynthesis.
Life History
Winter or colder periods are passed as late nymphal stages on the undersides of leaves. These may be on some remaining plants or weeds growing under benches. In the spring or when heat is applied adults will emerge and deposit eggs on the undersides of new plant growth. These eggs will hatch in 8 to 24 days, depending on the temperature. The nymphal stage will last from 23 to 30 days. Overall the life cycle from egg to adult will vary from 41 days to more than 300. The adult will live as long as 27 days.
CONTROL
Controls are difficult because the eggs and nymphs are located on the underside of leaves, and they may also be resistant to some aerosol chemicals. Adult control usually will involve multiple applications as the nymphs mature and all have emerged as adults. Some of the new synthetic pyrethroids make controls much more successful. However, chemicals must be alternated to lessen the chance of a chemical-tolerant or resistant population developing. In some states biological control using Encarsia lahorensis has been very successful. This parasitoid should be functional in the Gulf Coast states and warmer areas of other states. For specific chemical control recommendations see your county Cooperative Extension publications on ornamental plant pests.
Figure 176. Citrus whitefly. A. Adult. B. Eggs. C. Pupa. D. Infested gardenia leaf.
Greenhouse Whitefly
Greenhouse whitefly (Figure 177), Trialeurodes vaporariorum (Westwood), Aleyrodidae, HOMOPTERA
DESCRIPTION
Adult
About 1.5 mm long, the adult is a white insect that resembles a tiny moth (Figure K).
Egg
The small oblong eggs, pale green to purple, are deposited on the lower leaf surface, often in a circle or a crescent.
Nymph
The first instar nymph is mobile and similar to a scale insect crawler (Figure T). Later nymphal stages are yellowish with red eyes, and are immobile. They resemble soft scale insects, but have an orifice on the back through which honeydew is expelled.
Pupa
The oval pupa is pale green to black when parasitized. The normal color, when empty, is clear-glassy with a fringe of glassy setae, and with some long glassy setae on the dorsal surface (Figure U). The pupal case sits upon a vertical palisade of closely appressed wax rods (these are readily visible in side view).
BIOLOGY
Distribution
Greenhouse whiteflies are worldwide pests of greenhouse-grown ornamentals and vegetables. First discovered in England in 1856, they were found in the northeastern United States in 1870. Tropical Central or South America are suggested origins of the greenhouse whitefly.
Host Plants
Greenhouse whiteflies infest a wide variety of ornamental and vegetable crops, and they can survive outdoors during the growing season, particularly in sheltered locations. Even trees may be infested (redbud, Kentucky coffee berry, and avocado).
Damage
Infested plants become chlorotic and unthrifty. Honeydew and sooty mold further detract from the appearance of the crop. Unless controlled, greenhouse whiteflies may completely destroy the commercial value of floricultural crop.
Life History
Greenhouse whiteflies reproduce relatively slowly (one generation every 30 to 45 days), but each may lay up to 400 eggs and live as long as 2 months. Adults are usually found on the lower surface of new leaves. The new crawlers move about the plant for a day or two, often from leaf to leaf before inserting their mouthparts to feed. Once this occurs they probably do not move again until mature. The crawlers molt into nymphs and then into pupae. Finally, a new generation of whitish yellow adults emerges. They are soon covered by a white waxy bloom.
CONTROL
Lower greenhouse temperatures used in the culture of some bedding and potted plant varieties tend to encourage infestations, because naturally occurring parasitic wasps (Encarsia formosa) are reproductively inhibited at temperatures below 24°C (75°F) (Figure V).
Control of whiteflies is difficult because the eggs and immature forms are resistant to many aerosol and insecticide sprays. One must make regular applications of pesticides to control emerging adults until the last of a whole generation of immature whiteflies has emerged. However, some of the synthetic pyrethroid and synthetic insect growth-regulator pesticides are extremely effective and need not be applied as often. For specific chemical control recommendations, see your county Cooperative Extension publications on ornamental plant pests.
Figure 177. Greenhouse whitefly. A. Adult. B. Egg. C. Crawler. D. Pupa.
Figure K. Greenhouse whiteflies.
Figure T. Greenhouse whitefly nymph.
Figure U. Greenhouse whitefly pupa (top) and silverleaf whitefly pupa.
Figure V. Encarsia formosa emerging from a silverleaf whitefly pupa (bottom); parasitized silverleaf pupa (upper left); greenhouse whitefly pupa (upper right).
Silverleaf Whitefly
Silverleaf whitefly (Figure 178), Bemisia argentifolii Bellows and Perring, Aleyrodidae, HOMOPTERA
DESCRIPTION
Silverleaf Whitefly
Thoracic tracheal folds relatively narrow, wax at marginal opening of tracheal folds relatively narrow, the posterior wax no wider than the bases of the caudal setae, fourth anterior submarginal setae absent; causes white stem symptom on poinsettia and silverleaf on squash.
Sweetpotato Whitefly
The description is slightly different from the silverleaf whitefly. Thoracic tracheal folds relatively wide, wax at marginal opening of tracheal folds relatively wide, the posterior wax no wider than the bases of the caudal setae, fourth anterior submarginal setae present; does not cause white stem symptom on poinsettia nor silverleaf on squash.
Adult
The silverleaf whitefly is slightly smaller (about 0.96 mm in the female and 0.82 mm in the male) and slightly yellower than most other whitefly pests of flowers. The head is broad at the antennae and narrow towards the mouth parts. The wings are held roof-like at about a 45° angle, whereas other whiteflies usually hold the wings nearly flat over the body. Hence, the silverleaf whitefly appears more slender than other common whiteflies.
Egg
The eggs are inserted on end in the undersides of new leaves. The eggs are whitish to light beige with the apex tending to be slightly darker.
Nymph
The nymphal stages appear glassy to opaque yellowish and may or may not have dorsal spines, depending on leaf characteristics. The body is flattened and scale-like with the margin relatively near the leaf surface (Figure S). There is not a marginal palisade of waxy spines.
Pupa
The pupa or fourth nymphal instar will be somewhat darker beigeish yellow and opaque and 0.6 to 0.8 mm long. Pupae are relatively more plump compared to previous nymphal stages (Figure U). The apex of anterior and caudal spiracular furrows have smalls amount of white wax deposits. The caudal setae are prominent, and the caudal end is somewhat acute. Dorsal spines are present when the host leaf is hairy and absent when the host leaf is smooth.
BIOLOGY
Distribution
Silverleaf whitefly probably occurs around the world in tropical and subtropical areas and in greenhouses in temperate areas. It has been reported from California, Florida and it occurs in North Carolina.
Host Plants
Alfalfa, beans, brocolli, Citrus, Ficus, Lantana, lettuce, melons, cotton, grape, sweet potato, and poinsettia are definite hosts of the silverleaf whitefly. Gerbera daisies are probably hosts.
Damage
Direct damage is caused by the removal of sap, and indirect damage as a disease vector. The silverleaf whitefly is a vector for several important virus diseases of lettuce and melons in the southwestern United States. Both the adult and nymphal stages contribute to direct damage. Chlorotic spots sometimes appear at the feeding sites on leaves, and heavy infestations cause leaves of cucurbits and stems of poinsettias to blanch ("silver") and wilt. The excretion of honeydew and the subsequent development of sooty mold fungi also reduces the appearance, photosynthesis, and other physiological functions of the plant. Even though the silverleaf whitefly is considered an economic pest, economic thresholds have not been generated for this pest on ornamental plants.
Life History
(The following information was observed with whiteflies that were undoubtedly silverleaf whiteflies although at the time they were thought to be sweetpotato whiteflies.) Developmental times from egg deposition to adult emergence appears to be primarily controlled by temperature, humidity, and host plant. These times will vary from 16 to 38 days depending on these factors. The number of eggs laid by each female over her lifetime varies considerably, but appears to be around 80 to 100. There have been reports (in Israel) that repeated applications of insecticides have produced a highly fecund (300 eggs/females) strain of silverleaf whitefly. Apparently, at temperatures above 36°C eggs fail to hatch. "Crawlers" hatch from the eggs and crawl about until they insert threadlike mouthparts into the underside of the leaf to feed. They tuck their legs and antennae underneath and settle down closely to the leaf surface.
Crawlers molt into scalelike nymphs that also suck out sap. Nymphs molt a second and third time. The fourth stage eventually becomes a nonfeeding pupa. The adult whitefly develops within the pupa. Adults emerge from the pupa through a T-shaped slit about a month from the time the egg was laid. Females live about two weeks.
CONTROL
Control of silverleaf whiteflies is difficult because the eggs and older immature forms are resistant to many aerosol and insecticide sprays (in addition, the adults are extremely resistant to dry pesticide residue). For good control, the pesticide mixture must be directed to the lower leaf surface where all stages of the whiteflies naturally occur. One must make regular applications of pesticides to control crawlers and second stage nymphs until the last of a whole generation of immature whiteflies has hatched. However, some of the pyrethroid pesticides are somewhat more effective and need not be applied as often. Neem seed extract is not as acutely toxic as some of the synthetic pesticides, but has the advantage of being toxic to young nymphs, inhibiting growth and development of older nymphs, and reducing oviposition by adults. For specific chemical control recommendations, see your Cooperative Extension publications on ornamental plant pests.
Figure 178. Silverleaf whitefly. A. Adult. B. Egg. C. Crawler. D. Nymph.
Publication date: Jan. 1, 1994
AG-136
Other Publications in Insect and Related Pests of Flowers and Foliage Plants
- Aphids Found on Flowers and Foliage
- Beetles Found on Flowers and Foliage
- Bugs Found on Flowers and Foliage
- Caterpillars Found on Flowers and Foliage
- Flies and Maggots Found on Flowers and Foliage
- Leafhoppers Found on Flowers and Foliage
- Mealybugs Found on Flowers and Foliage
- Mites Found on Flowers and Foliage
- Scale Insects Found on Flowers and Foliage
- Slugs and Snails Found on Flowers and Foliage
- Thrips Found on Flowers and Foliage
- Whiteflies Found on Flowers and Foliage
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