Nipaecoccus viridis (Newstead)
(Synonym: Nipaecoccus vastator Maskell).
Taxonomic placing: Insecta, Hemimetabola, Hemiptera, Sternorrhyncha, Coccomorpha, Coccoidea, Pseudococcidae.
Common names: Sphereical mealybug, Lebbeck mealybug, Karroo thorn mealybug.
Geographical distribution: The pest is present on both sides of the African-Syrian rift, from South to North Africa and to the North of Israel.
Host plants: The pest attacks over 100 plant species in more than 30 families. Major crops include soybean, citrus, mango, tamarind, pomegranate and grapevines. It is a common pest of ornamentals such as Mimosaceae and Moraceae, Hibiscus spp. and Ziziphus spp. In the laboratory the mealybug can be reared on potato sprouts.
Morphology: The adult female is oval; body segmentation is visible prior to oviposition and covered by wax. The body is dark green purple, or dark brown purple, beneath the white-creamy or pale-yellowish wax cover; it is 2.5-4 mm long and 1.5-3 mm wide, depending on the host plant and the specific feeding site. The adult male is brown-purple with well developed forewings, its elongated body is 1.3-2.5 mm long. The ovisac is hemispherical, composed of white loose wax filaments and may contain several hundred eggs. Large females may lay more than 1000 eggs. The female nymph and the two early male nymphal instars resemble the female, but are smaller, being purple. Later they become darker and covered with wax. The male pupa is light-brown to purple and develops in a loose cottony-white cocoon.
Life cycle: Females undergo 3 nymphal stages, often moving a little after each molt to change their feeding sites. They may live up to 50 days, dying soon after depositing all eggs. The male develops through two larval instars, plus prepupal and pupal stages; it stops feeding in the former stage and seeks a pupation site, away from the colony, often in aggregates. Female development is slightly faster than that of the male (20 days versus 19 days) at 25°C, whereas at 32°C female development is slower (19 days versus 15 days). Males, which live up to three days and die after copulation, usually emerge along with the young adult females. The male to female ratio is 1:2. The mealybug reproduces sexually; parthenogenesis has been reported but remains in doubt. Females begin to secrete an ovisac about a day after mating, and 3-7 days later begin to lay eggs, for a period of 6-15 days. Egg survival is adversely affected by high relative humidities (above 60) and temperatures below 20°C. The emerging crawlers move away from the hatching site, aggregating in cracks on stems, twigs, leaves or young fruits. They may crawl long distances and can easily be dispersed by winds. All stages feed on host phloem and parenchyma.
Seasonal history: In the Middle East the pest overwinters as an adult on the stem and main branches of the trees, usually in cracks and crevices where callus tissues have covered recent wounds, in girdling scars and around grafting sites. The crawlers migrate during spring to strongly growing tissues, mainly young shoots and fruit, later colonizing the calyx area. If undisturbed, in due course the colony covers the upper surface of citrus fruits along with the twig to which they are attached. Light infestations can be detected by watching ant activities. Heavy infestations occur from mid-summer onward. The mealybug raises 6-7 annual generations in the Jordan Valley, 4-5 during the warm season, when each lasts 5-6 weeks.
Economic importance: Injury is related to the pest’s pattern of colonizing host plants and to the specific susceptibility of their cultivars. On citrus, of which it is a major pest in the Middle East, the pest frequently causes curling and dwarfing of young growth. Heavy infestations result in deterioration of the crown, which turns yellow, wilts and eventually dies. The mealybug occurs on all plant parts and presumably injects toxins into the host, causing the injuries described above. It prefers to colonize fast growing tissues, contaminating them with honeydew, which results in a thick cover of sootymold. Young fruits may drop as a result of such infestations. Affected fruits develop unsightly lumps and corky scars around sites where the colony feeds, distorting the round shape of the fruit. Heavily infested fruits may turn yellow and drop. This type of injury is typical of outbreaks that occur upon the pest’s invasion of new regions or sites. The severity of such infestations is later reduced, once the pest’s specific parasitoids find the host or, following insecticide misuse, have re-colonized the orchard. In addition, fruit moths are often associated with mealybug-infested fruit, compounding the injury. However, even small, latent mealybug populations may cause severe damage to susceptible citrus varieties, due to injury caused by 1st- instar larvae during their early feeding period. These symptoms include irregular watery green spots on the peel of ripe fruits, which renders them unmarketable. The spots result from microscopic injuries caused by pest individuals, which usually do not survive or abandon the young fruit.
In the Middle East the yellow citrus varieties, Marsh grapefruit, red grapefruit, pummelo and Sweetie (Citrus paradisi X C. grandis) are more susceptible.
Management
Chemical control: Since the activities of natural enemies do not suffice to prevent infestations of young fruit of susceptible citrus varieties, the watery green spots can be prevented by a spring application of the organophosphate chlorpyriphos or of acetamiprid. The former is needed in early summer when large populations occur, populations that usually result from the eradication of natural enemies due to the misuse of insecticides, or to a delay in natural enemy recovery after a very cold winter. Pesticides applied onto the grafting position is an effective preventive measure in permanently infested sites.
Biological control: About 30 species of primary hymenopterous parasitoids were reared from pest colonies. Most are Encyrtidae. In Israel Anagyrus indicus, Anagyrus sp. near pseudococci, Leptomastix nigrocoxalis Compere and Pseudaphycus near perdignus are the more prominent. Anagyrus indicus was successfully introduced into Jordan in the early 1980’s. Control in Egypt was achieved by introducing L. nigrocoxalis (as Leptomastix phenacocci Compere) and Anagyrus aegyptiacus Moursi from Java. Ants carry the mealybugs inside and between trees, disrupting parasitoid activity. Over 25 species of predators have been recorded from pest populations, with the dominant being Coccinellidae, (Neuroptera, Chrysopidae and larvae of Cecidomyiidae. Few species of Scymnus (Coccinellidae) were reared from mealybug colonies in the Jordan Valley. Indigenous predators of other mealybugs, mainly those attacking the citrus mealybug, shifted to the spherical mealybug after it invaded new areas.
References
Bartlett, B.R. 1978. Pseudococcidae. In: Clausen C. P. Introduced Parasites and Predators of Arthropod Pests and Weeds: A World Review, pp 146-148. ARS, USDA, Agric. Handbook 480, 545 pp.
Ghosh, A.B. and Ghosh, S.K. 1989. Description of all instars of the mealybug Nipaecoccus viridis (Newstead) (Homoptera, Pseudococcidae). Environment and Ecology 7: 564-570.
Meyerdrik, D.E., Khasimuddin, S. Bashir, M. 1988. Importation, colonization and establishment of Anagyrus indicus (Hym. : Encyrtidae) on Nipaecoccus viridis (Hom., Pseudococcidae) in Jordan. Entomophaga 33: 229-237.
Shaaraf, N.S. and Meyerdrik, D.E. 1987. A review on the biology, ecology and control of Nipaecoccus viridis (Homoptera: Pseudococcidae). Miscellaneous Publication of the Entomological Society of America 66: 1-18.
Sharaf, N. S. 1997. Host plants and natural enemies of mealybugs and other related Homopterans, with special reference to the spherical mealybug Nipaecoccus viridis (Newstead), in Jordan. Dirasat Agricultural Sciences 24: 383-390.
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AUTHORS
Zvi Mendel. E-mail: zmendel@volcani.agri.gov.il
Agricultural Research Organization; The Volcani Center Department of Entomology; P.O. Box 6, Bet-Dagan, 50250, Israel. Tel: 972-3-9683636 Fax: 972-3-9683849
Daniel Blumberg. E-mail: dblum@volcani.agri.gov.il
Agricultural Research Organization; The Volcani Center Department of Entomology; P. O. Box 6, Bet Dagan 50250, Israel. Tel.: +972-3-9683518; Fax: +972-3-9604180