Silverleaf whitefly, also known as the sweet potato whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae; Fig. 1), attack a wide range of plants, from ornamentals to warm-season vegetables in the U.S. Whiteflies are active from mid-July to mid-October and are found gather together on the underside of the leaves during the daytime (Fig. 2). Although 76 whitefly species are known to exist in the southeastern U.S., only a few species, such as the greenhouse whitefly (Trialeurodes vaporariorum), banded wing whitefly (Trialeurodes abutiloneus), giant whitefly ( Aleurodicus dugesii), citrus whitefly (Dialeurodes citri), cloudywinged whitefly (Dialeurodes citrifolii), and the sweet potato whitefly cause serious problems in greenhouses and nurseries. Among several whitefly species, the silverleaf whitefly, particularly biotype B (Fig. 3), is the most common and destructive whitefly species in nurseries in the southeastern U.S.
Photo credit: Central Science Laboratory, Harpenden, British Crown, Bugwood.org
Photo credit: Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org
Photo credit: Scott Bauer, USDA Agricultural Research Service, Bugwood.org
Biology and damage
The silverleaf whitefly adults have a whitish waxy coating covering their body and four wings. The adults silverleaf whiteflies are approximately 0.8 mm (male) to 1.2 mm (female) long. Silverleaf whitefly is yellowish-white and smaller than other whitefly species, such as giant whitefly, greenhouse whitefly,andbanded wing whitefly. The life stages of whiteflies include egg, nymph, pupa, and adult. Unlike all other whitefly species, silverleaf whiteflies do not lay eggs in a circular pattern. On the underside of leaves, a female deposit from 50 (in cold conditions) to 400 (in warmer conditions) yellow-colored eggs (Fig. 4). The eggs remain partially inserted in the surface of leaves. The color of eggs turns from yellow to purplish-brown just before hatching. Eggs hatch between 4 and 12 days, depending on temperature, into flattened nymphs. The first instar nymphs have six functional legs and antennae and are referred to as crawlers. Once the crawlers find feeding sites on host leaves, they settle down by inserting their mouthparts and begin to consume plant juice. They lose their appendages (legs and antennae) after molting to second instar nymphs (Fig. 5). The later nymphal stages remain on the feeding site for the rest of their development. They undergo four nymphal stages, and the final fourth nymphal stage is referred as a pupa, distinguished by visible red eyes (Fig. 6). Whitefly adults emerge from the pupal stage. They live approximately one month. The silverleaf whitefly can complete a life cycle between 16 and 31 days.
Plant damage occurs because of direct feeding or indirect transmission of plant pathogens, such as plant viruses, through feeding. Adults and developing nymphs of whiteflies (Fig. 7) consume plant sap and cause severe yellowing of leaves (Fig. 8), stunting, rapid drying of foliage, and premature leaf drop. Young plants rarely survive severe whitefly infestation and excessive feeding. In addition, whiteflies excrete excess sugary liquid referred to as honeydew. Honeydew is colonized by sooty mold fungi, which produce a black coating on the leaf surface. The black sooty mold reduces aesthetic appeal, marketability as well as plant health due to lack of photosynthesis.
Host plants
Sweet potato whitefly is polyphagous and can infest and consume plants from multiple families. More than 500 plant species ranging from ornamentals to vegetables are potential hosts for silverleaf whiteflies. In nursery or greenhouse production, silverleaf whiteflies are often found on poinsettia (Euphorbia pulcherrima), begonia (Begonia x semperflorens-cultorum), hibiscus (Hibiscus rosa-sinensis), gerbera (Gerbera jamesonii), lantana (Lantana camara), verbena (Verbena bonariensis), chrysanthemum (Chrysanthemum morifolium), salvia (Salvia officinalis), roses (Rosa spp.), rhododendron (Rhododendron ferrugineum), and sweetgum (Liquidambar styraciflua).
Photo credit: Shimat V. Joseph, University of Georgia.
Photo credit: Shimat V. Joseph, University of Georgia
Monitoring and management
In nurseries, whitefly infestations are a persistent problem as infested plants are continuously being introduced. Preventing the introduction of whitefly-infested plants to the nursery should be the primary strategy for effective whitefly management. Regular inspections and immediate insecticide applications are necessary to protect plants from whitefly introductions once infested plants are detected in the facility. Isolation of newly introduced plant stock for 1-2 weeks before planting can also reduce infestations to nursery plants. Whiteflies are particularly attracted to plants that are at bloom, especially plants with yellow flowers. Regular monitoring of the plants and physically removing infested leaves with a high infestation can reduce the whitefly population. Prompt removal of plant residues and weeds from the nursery may help reduce whiteflu nymphs and pupae. Whiteflies can be monitored using yellow sticky cards deployed at canopy height. If monitored on the plant, it is critical to check for whiteflies on the underside of leaves.
Many biological agents can control the whitefly population. Beneficial insects, such as lacewing (Neuroptera: Chrysopidae or Hemerobiidae) larvae, adult and nymphs of minute pirate bugs (Hemiptera: Anthocoridae), and lady beetles (Coleoptera: Coccinellidae), can effectively feed on whitefly eggs and nymphs. Parasitoids, such as Eretmocerus eremicus (Hymenoptera: Aphelinidae), are effective in controlling silverleaf whiteflies in greenhouses. A predatory beetle, such as Delphastus catalinae (Coleoptera: Coccinellidae), effectively consumes eggs and nymphs.
Insecticides are an effective tool for whitefly control in nurseries and landscapes. Because whiteflies infest the undersurface of the leaves, adequate insecticide coverage or use of translaminar (moves across the leaf blade) products are essential. Whitefly populations can be successfully controlled with 4-5 applications at 5-7 day intervals. Rotating insecticides with distinctly different modes of action are critical to delaying insecticide resistance. Refer to the insecticide resistance action committee webpage (https://irac-online.org/modes-of-action/) as guide to determine insecticide class, and do not select insecticides within the same category number (class) for back-to-back sprays. Many contact and systemic insecticides are effective whiteflies organophosphates (such as acephate, and malathion), neonicotinoids (such as imidacloprid, and dinotefuran), pyrethroids (such as cyfluthrin, and bifenthrin), and insect growth regulators (such as pyriproxyfen, and buprofezin). Biorational insecticides such as insecticidal soaps, horticultural oils, neem oil, and petroleum-based oils can also effectively control whiteflies. Carefully read the insecticide label before application because the label is the law! Contact your nearest county extension office for the latest insecticide recommendations for whitefly control in nursery and greenhouse by calling 1-800-ASK-UGA1.
References
Barrett, B. A. (2012). Managing whiteflies on indoor and outdoor plants (2012). Lawn and garden. University of Missouri Extension. Retrieved from https://extension.missouri.edu/ publications/g7275
Dale, A. (2017). MG254 Managing whiteflies on landscape ornamentals. EDIS (1). University of Florida IFAS Extension. Retrieved from https://journals.flvc.org/edis/article/view/104456
Hoddle, M. The biology and management of the silverleaf whitefly, Bemisia argentifolii Bellows and Perring (Homoptera: Aleyrodidae) on greenhouse grown ornamentals. University of California Riverside Applied Biological Control Research. Retrieved from http://biocontrol.ucr.edu/bemisia.html
Osborne, L. S., & Landa, Z. (1992). Biological control of whiteflies with entomopathogenic fungi. Florida Entomol. 75:456-471.
Sani, I., Ismail, S. I., Abdullah, S., Jalinas, J., Jamian, S., & Saad, N. (2020). A review of the biology and control of whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae), with special reference to biological control using entomopathogenic fungi. Insects 11: 619.
Schlaeger, S., Pickett, J. A., & Birkett, M. A. (2018). Prospects for management of whitefly using plant semiochemicals, compared with related pests. Pest manage. Sci. 74: 2405-2411.
van Iersel, M. W., Oetting, R. D., & Hall, D. B. (2000). Imidacloprid applications by subirrigation for control of silverleaf whitefly (Homoptera: Aleyrodidae) on poinsettia. J. Econ. Entomol. 93: 813-819.
