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Citrus Blackfly, Aleurocanthus woglumi Ashby (Homoptera:Aleyrodidae)1
Ru Nguyen and Avas B. Hamon2Introduction
Citrus blackfly, Aleurocanthus woglumi Ashby, a serious citrus pest of Asian origin (Dietz and Zetek 1920), was discovered in the western hemisphere, in 1913 in Jamaica. It spread to Cuba in 1916, Mexico in 1935 (Smith et al. 1964) and was detected in Key West, Florida in 1934. It was eradicated from Key West in 1937 (Newell and Brown 1939). Rediscovered in Ft. Lauderdale, Florida in 1976 (Dowell et al. 1981), citrus blackfly was detected in Palm Beach and Dade counties in 1977; Lee, Highlands and Brevard counties in 1979; Manatee County in 1986; Polk County in 1989; Marion and Volusia counties in 1991; and Alachua County in 1992 (Nguyen, unpublished data). At present, it is widely spread over central and south Florida from Cross Creek to Key West.Economic Importance
Citrus blackfly infests over 300 host plants, but citrus ( Figure 1 ) is the most suitable for large population development. It damages citrus by sucking nutrients from foliage which weakens the plants. Citrus blackflies excrete honeydew on which sooty molds develop. Sooty molds coat citrus leaves, causing them to appear black. Sooty molds can severely impair leaf respiration and photosynthesis.
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Figure 1. Citrus black fly damage. Description and Life History
Eggs are laid in a spiral pattern ( Figure 2 ) on the underside of the leaf. Each female lays 2-3 egg spirals during her 10-14 day life span. Eggs hatch within 7-10 days (Dowell et al. 1981). The first instar (Figure 2) is elongate-oval, averaging 0.30 mm long x 0.15 mm wide and is brown in color, with two glassy filaments curving over the body. The first instar lasts 7-16 days. The second instar is more ovate and convex than the first instar, averaging 0.40 mm long x 0.20 mm wide, and is dark brown in color with numerous spines covering the body. The second instar lasts 7-30 days. The third instar is more convex and much longer than the second, averaging 0.87 mm long x 0.74 mm wide. The body is shiny black with spines stouter and more numerous than those in the second instar. The third instar lasts 6-20 days (Dietz and Zetek 1920, Smith et al. 1964). The fourth instar, or so-called pupal case ( Figure 3 ), is ovate and shiny black with a marginal fringe of white wax. The sex is readily distinguishable. Females average 1.24 mm long x 0.71 mm wide; males are 0.99 mm long x 0.61 mm wide. The pupal stage lasts 16-50 days (Dietz and Zetek 1920, Dowell et al. 1981). The life cycle from egg to adult ranges from 45 to 133 days depending on the temperature (Dietz and Zetek 1920). Six generations per year are produced in south Florida (Nguyen et al. 1983). The adult ( Figure 4) emerges from a T-shaped split appearing in the anterior end of the pupal case. At emergence the head is pale yellow, legs are whitish, and eyes are reddish brown. Within 24 hours after emergence the insect is covered with a fine wax powder which gives it a slate-blue appearance (Dietz and Zetek 1920).
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Figure 2. Citrus black fly eggs laid in a spiral pattern and first instars.
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Figure 3. Pupal case.
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Figure 4.
Biological Control
Citrus blackfly has several natural enemies. In Florida, the most effective agents for controlling citrus blackfly are the parasitic wasps Encarsia opulenta Silvestri and Amitus hesperidum Silvestri (Hart et al. 1978). Female A. hesperidum ( Figure 5 ) lay eggs in all three larval stages of citrus blackfly with a preference for the first stage. A female citrus blackfly larva will support two and occasionally three or four parasites while a male citrus blackfly larva will support only one parasite ( Figure 6 ). Development of A. hesperidum is synchronized with its host-adult female parasites are ready to lay eggs when the susceptible larval stages of citrus blackfly are present. Each female parasite can produce up to 70 offspring in 4-5 days with adequate hosts available. However, this parasite has poor searching ability and a short life span. A. hesperidum is most effective with high density citrus blackfly populations, especially during cool temperature and high humidity seasons. An A. hesperidum population will expire soon after suppression of the citrus blackfly population (Nguyen et al. 1983). E. opulenta ( Figure 7 ) has a lower rate of reproduction than A hesperidum, but has better searching ability. Females may survive up to 6 weeks. Generally, E. opulenta can maintain a citrus blackfly population at a lower level than A. hesperidum. Mated females of E. opulenta lay a single diploid egg in any larval stage of the host, although the second stage appears preferable ( Figure 8 ). This egg will produce a female parasite. Virgin female E. opulenta may deposit a haploid egg in a fully-developed female larva of E. opulenta (her own species) and this egg will produce a male parasite (adelphoparasite). The sex ratio in the field is 1:7 (male:female) (Smith et al. 1964, Nguyen 1987).
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Figure 5. A. hesperidum.
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Figure 6. Parasitized citrus black flies.
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Figure 7. E. opulenta.
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Figure 8. E. opulenta eggs laid in citrus black flies. Literature Cited
Dietz, H. F. and J. Zetek. 1920. The blackfly of citrus and other subtropical plants. USDA Bulletin 885:1-55.Dowell, R. V., R. H. Cherry, G. E. Fitzpatrick, J. A. Reinert, and J. L. Knapp. 1981. Biology, plant-insect relations, and control of the citrus blackfly. Florida Agricultural Experiment Station Bulletin 818: 1-48.
Hart, W. G., A. Selhime, D. P. Harlan, S. J. Ingle, M. Sanchez-R, R. H. Rhode, C. A. Garcia, J. Caballero, and R. L. Garcia. 1978. The introduction and establishment of parasites of citrus blackfly, Aleurocanthus woglumi in Florida (Hem.:Aleyrodidae). Entomophaga 23: 361-366.
Newell, W., and A. C. Brown. 1939. Eradication of the citrus blackfly in Key West, Fla. Journal Economic Entomology 32: 680-682.
Nguyen, Ru. 1987. Encarsia opulenta (Silvestri) a parasite of Aleurocanthus woglumi Ashby (Hemiptera:Aphelinidae). Florida Department of Agriculture & Consumer Services, Division of Plant Industry, Entomology Circular No. 301:1-2.
Nguyen, Ru, J. R. Brazzel, and C. Poucher. 1983. Population density of the citrus blackfly, Aleurocanthus woglumi Ashby (Homoptera:Aleyrodidae), and its parasites in urban Florida in 1979-81. Environmental Entomology 12: 878-884.
Smith, H. D., H. L. Maltby, and E. J. Jimenez. 1964. Biological control of the citrus blackfly in Mexico. USDA-ARS, Technical Bulletin No. 1311: 1-30.
Footnotes
1. This document is CIR 360, one of a series of the Entomology and Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date September 1993. Reviewed May 2003. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.2. Ru Nguyen, Entomologist, Bureau of Methods Development and Biological Control, and Avas B. Hamon, Taxonomic Entomologist, Bureau of Entomology, Nematology, and Plant Pathology, Division of Plant Industry, P.O. Box 147100, Gainesville, Florida 32614-7100.
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