Dialeurodes citri (Ashmead)
Taxonomic placing: Insecta, Hemimetabola, Hemiptera, Sternorrhyncha, Aleyrodidae.
Common name: Citrus whitefly.
Geographical distribution: This whitefly occurs in Asia, North and South America, Europe, Russia and the Mediterranean region. CIE Map #111.
Host plants: Dialeurodes citri is polyphagous; among citrus species and varieties it prefers orange and easy peeler cultivars.
Morphology: The adult is about 1.5 mm in length, with white wings and a yellow body covered with white wax. The bodies of the first three nymphs are transparent, whitish; the fourth-instar nymph, during which the insect pupates, has a Y-like mark on its body.
Life cycle: On citrus in Israel the pest usually completes three annual generation, in April-June, in July-August and the third, which usually overwinters, lasts until the following spring. A small fraction (5%) of the population develops in the autumn, thus creating a fourth generation whose adults also emerge in the spring. The threshold of development is at 11.3°C. Reproduction is by arrhenotoky and the stalked eggs (about 90-110/ female) are inserted into the lower leaf sides; young, fully-extended leaves are preferred. The inner, shaded parts of trees are preferred for oviposition. Under long day conditions a generation requires about 7-8 weeks at 25°C. The adults live for about two weeks.
Economic importance: Damage is mostly due to the copious amounts of honeydew secreted by the nymphs and colonized by sootymold fungi. This contaminate the fruit, obstructs respiration and disrupts photosynthesis, leading to leaf drop and yield reduction. Heavily-infested leaves become intermittently white-and black, due to the pests’ coloring and the sooty mold.
Management
Sampling: Due to the oviposition preferences of the pest, only young, fully-extended leaves should be sampled during its first generation. Four leaves/tree, one from the interior of each examined tree plus three from the periphery, preferably from the northern and southern sides should be taken. For first-generation egg sampling, a precision level of 0.30 can be achieved by leaves from 11 trees, a total of 44 leaves. For the second and third generation egg sampling, leaves from nine trees, a total of 36, would suffice to obtain a precision level of 0.25. For larval sampling (which incorporate threshold sooty mold levels), in the first generation seven trees (28 leaves) may be taken for the same precision level, whereas nine trees (36 leaves) should be sampled for the second and third generations.
Mechanical control: The sootymold can be washed away with soaps before marketing.
Chemical control: IGRs are very effective. When applied in late April to early May they kill the developing eggs, and in early June they affect the molting pest. Chemical treatments should be considered only for very heavy infestations, in order to rapidly reduce pest numbers prior to the release of natural enemies.
Biological control: Two introduced Aphelinid endoparasitoids, Encarsia lahorensis (Howard) and and an Encarsia sp., attack the pest. Several Coccinellidae, namely Clitostethus arcuatus (Rossi) and Serangium parcesetosum Sicard, also feed on the pest and may reduce its populations.
References
Argov, Y., Rossler, Y., Voet, H. and Rosen, D. 1999. The biology and phenology of the citrus whitefly, Dialeurodes citri, on citrus in the coastal plain of Israel. Entomologia Experimentalis et Applicata 93: 21-27.
Argov, Y., Rossler, Y., Voet, H. and Rosen, D. 1999. Spatial dispersion and sampling of citrus whitefly, Dialeurodes citri, for control decision in a citrus orchard. Agricultural and Forest Entomology 1: 305-318.
Argov, Y. Rossler, Y., Voet, H. and Rosen, D. 2000. Introducing Encarsia lahorensis against Dialeurodes citri in Israel: a case of successful biological control. BioControl 45: 1-10.
Bar-Zakay, I. 1992. IGR’s in Citrus: achievements versus problems. Hassadeh 72: 572-575 (in Hebrew with an English abstract).
Metwally, S.M., Shenishen, Z., Boraei, H.A., El-lleneidy A.H. and Mesbah, A.H. 1999. Clitostethus arcuatus (Rossi) (Coleoptera: Coccinellidae) a predator species, of the citrus whitefly, Dialeurodes citri (Ashm.) (Homoptera: Aleyrodidae) in Egypt. Egyptian Journal of Biological Pest Control 9: 61-66.
Uygun, N., Ohnesorge, B. and Ulusoy, R. 1990. Two species of whiteflies on citrus in Eastern Mediterranean: Parabemisia myricae (Kuwana) and Dialeurodes citri (Ashmead). Morphology, biology, host plants and control in Southern Turkey. Journal of Applied Entomology 110: 471-482.
Yigit, A., Canhilal, R. and Ekmekci, U. 2003. Seasonal population fluctuations of Serangium parcesetosum (Coleoptera: Coccinellidae), a predator of citrus whitefly, Dialeurodes citri (Homoptera: Aleyrodidae), in Turkey’s eastern Mediterranean citrus groves. Environmental Entomology 32: 1105-1114.
Website
Yael Argov, The Israel Cohen Institute for Biological Control, Citrus Marketing Board of Israel, P.O. Box 80, 50250 Bet Dagan, Israel. E-mail: yael@jaffa.co.il