Return to:

Hosts

In Hawaii this scale attacks several ornamental plants including Crytomiun and other ferns, Clermontia parviflora, Pipturus, Solanum santiwongsei (Zimmerman, 1948), Dendrobium orchids, and proteas. Bittermelon is also a known host of the hemispherical scale. In other parts of the world, its main host is coffee, and alternative hosts include tea, Citrus, guava, mango, and many other cultivated and wild plants (Hill, 1983).

Distribution

The hemispherical scale is distributed in the tropics and in some sub-tropical areas(Hill, 1983). In Hawaii, this scale is present on the Big Island, Kauai, Maui, and Oahu.

Damage

Hemispherical scales feed on plant juices and cause a loss of vigor, spots on the foliage due to toxins in the scale saliva, deformation of infested plant parts, loss of leaves, retarded plant growth, and even death of the plant (Dekle, 1965; Reinert, 1974; Beardsley and Gonsalves, 1975; Valand et al., 1989). In India, these scales have been responsible for causing premature death of pointed gourd vines (Valand et al., 1989). Hemispherical scales are found clustered on the shoots, leaves, and young fruit of plants. They are often arranged in an irregular line near the edge of the leaf blade (Hill, 1983).

Biology

Studies conducted by Ibrahim (1985) report the developmental time from egg to adult of hemispherical scales on green potato sprouts to be 95.2 days at 64.4° F (18° C) and 31.2 days at 82.4° F (28° C). This study showed that the hemispherical scale could thrive at temperatures between 64.4° F (18° C) and 82.4° F (28° C), with the optimal development occurring at 78.8° F (26° C) (Ibrahim, 1985). Within the viable temperature ranges of this scale, an increase in temperature accelerated the rate of development and a decrease in temperature lengthened development. However, lowering the rearing temperature increased the size of the scales (Ibrahim, 1985).

Male hemispherical scale males are rarely found. It is presumed that reproduction occurs primarily through parthenogenesis (reproduction without fertilization).

EGGS

The eggs are laid underneath the carapace of the adult female (Hill, 1983). The eggs are translucent or whitish just after oviposition and later turn pale yellow and ultimately orange (Ibrahim, 1985). They measure approximately 1/100 inch (0.25 mm) long and 1/200 inch (0.13 mm) wide (Ibrahim, 1985). A study conducted by Ibrahim (1985) reported that the eggs hatched in 23.6, 20.6, 15.6, 15.4, 13.6, and 12.2 days at 64.4û F (18° C), 68° F (20° C), 71.6° F (22° C), 75.2° F (24° C), 78.8° F (26° C), and 82.4° F (28° C), respectively.

NYMPHS

The first instars are called crawlers. They are flat, oval, greenish-brown to pale amber, have six legs (Hill, 1983; Ibrahim, 1985), and are about the same size as the eggs (Ibrahim, 1985). This is the only mobile stage of female hemispherical scales. Crawlers move about the leaf area in search of a suitable feeding sight until one is found (Hill, 1983). In warmer temperatures, 71.6° F (22° C) to 86° F (30° C), the crawlers settle at a feeding site in about 2 days; at cooler temperatures, 64.4° F (18° C) to 68° F (20° C), they settle in about a week (Ibrahim, 1985). The remaining two nymphal stages are essentially stationary at the site selected by the crawler, only under adverse conditions will female nymphs move small distances (Hill, 1983).

The body color of the last two instars ranges from pale yellow to greenish brown to dark pink (Hill, 1983; Le Pelley, 1968). The second and early third instar body shape has an irregular outline and lies flat (Ibrahim, 1985). Towards the end of the third instar, the scale undergoes a rapid growth phase, until it is about the size of the adult (Ibrahim, 1985). Refer to Zimmerman (1948) for a detailed description of the nymphs under a microscopic view.

In a study conducted by Valand et al. (1989) the developmental duration of the first, second, and third instars at 75.2° F (24° C) was 12.5, 21.0, and 20.4 days; at 80.6° F (27° C) 10.1, 25.2, and 19.9 days; at 86° F (30° C) 10.1, 23.7, and 13.1 days respectively.

ADULTS

The mature female scale has a convex, light to dark yellow-brown, smooth and polished, helmet-shaped carapace. When the scale occurs on flat surfaces, the carapace is almost hemispherical, but on small stems it is elongate (Zimmerman, 1948). The adult stage is incapable of locomotion and measures about 1/12 inch (2 mm) long (Hill, 1983). Refer to Zimmerman (1948) and Beardsley, et al. (1976) for detailed descriptions of adults under microscopic view. 

In a study conducted by Valand et al. (1989), where hemispherical scales were reared on pointed gourd, the adult longevity was determined to be 8.5, 7.8, and 8.4 days at 75.2° F (24° C), 80.6° F (27° C), and 86° F (30° C) respectively. Females have a 2 to 3 day waiting period before beginning to lay eggs and lay eggs for 4 to 6 days before dying. In the same study by Valand et al. (1989), the average number of eggs laid per female during her lifetime was 268, 547 and 488 at 75.2° F (24° C), 80.6° F (27° C) and 86° F (30° C) respectively.

Behavior

Since female armored scales are not capable of wandering once they have settled and started feeding, long range dispersal happens by passive transport of infested plant material. Short range dispersal happens as crawlers search out places to settle and feed (Beardsley and Gonsalves, 1975). The crawlers can be carried from place to place by people, animals, birds, ants, and wind currents (Dekle, 1965; Beardsley and Gonsalves, 1975). Wind is an agent of dispersal and also one of mortality, since crawlers dislodged by wind may not land on suitable host plants. Male crawlers tend to settle in clusters; the cause of this is not known. Males do not feed in the last two armored stages and after emergence from the armor. The adult males have wings but are capable of only weak flight or wind transport. Males live only a few hours, emerging in the late afternoon to mate. Mate finding is probably due to attraction to pheremones secreted by females (Beardsley and Gonsalves 1975). Because of their tiny size, short life, and evening activity, it is rare to find adult males in the field.

Management

Non-Chemical Control

Scales are usually brought into greenhouse situations with the introduction of infested plant material. All plant material going into the greenhouse should be thoroughly inspected for scales and other insects before being introduced (Copland and Ibrahim, 1985).

Infested trees should receive optimum quantities of mulch and fertilizer to enhance vigor (Hill, 1983). Infested branches can be cut off and left on the ground for parasite emergence (Hill, 1983). 

Several parasites known to attack this scale in Hawaii are Encyrtus infelix (Embleton), Encyrtus barbatus Timberlake, Tomocera californica Howard, and the waspsMicroterys flavus (Howard), Scutellista cyanea Motschulsky and Aneristus ceroplastae Howard (Zimmerman, 1948). Several biological control programs, intentionally planned to control the black scale (Saissetia oleae), have incidentally been successful in controlling the hemispherical scale in California, Guam and Chile (Clausen, 1978). An extensive list of wasps that are parasites of the hemispherical scale throughout the world is given by Le Pelley (1968). The hemispherical scale is usually controlled by its natural enemies, and chemical treatments are usually not necessary. 

Chemical Control

Sprays are effective on the early nymphal stages of scales. However, control is difficult on other life stages. Adults are firmly attached to the plant and remain attached, even after their death. The dead scales may give a false impression of the pest infestation status (Copland and Ibrahim, 1985). Eggs are protected by the waxy covering of the mother and are shielded from chemical sprays. Plant sensitivity to chemical sprays should also be determined since scales are often pests of sensitive ornamental plants (Copland and Ibrahim, 1985).

Chemicals used on scales are usually the same as those used on mealybugs and may include diazinon, dimethoate, formothion, malathion and nicotine (Copland and Ibrahim, 1985). Whenever any chemical is used, always consult the label, to determine the appropriate crop, pest, dose, and precautions.

A drenching spray of insecticidal oil followed by a second application 3 to 4 weeks later is effective against young scales (Hill, 1983). Soaps and other oils are also effective (Le Pelley, 1968).

There is no listing for malathion as of April 2007.

References

Beardsley, J.W. Jr. 1966. Insects of Micronesia, Homoptera: Coccoidea Volume 6, Number 7. Bernice P. Bishop Museum Press, Honolulu. 562 pages.

Beardsley, J.W. and R.H. Gonsalves. 1975. The Biology and Ecology of Armored Scales. Annual Review of Entomology. 20: 47-73.

Beardsley, J.W., J.A. Davidson, J.O. Howell, M. Kosztarab, D.R. Miller, S. Nakahara and M.B. Stoetzel. 1976. Workshop on Scale Insect Identification. Presented at the National Meeting of the Entomological Society of America in Hawaii. 115 pages.

Clausen, C.P. (Ed.). 1978. Introduced Parasites and Predators of the Arthropod Pests and Weeds: A World Review. Agricultural Handbook 480. United States Department of Agriculture, Washington D.C. 545 pages.

Copland, M.J.W. and A.G. Ibrahim. 1985. Chapter 2.10 Biology of Glasshouse Scale Insects and Their Parasitoids. pp. 87-90. In: Biological Pest Control The Glasshouse Experience. Eds. Hussey, N.W. and N. Scopes. Cornell University Press; Ithaca, New York. 

Dekle, G. W. 1965. Arthropods of Florida Vol. 3, Florida Armored Scale Insects. Division of Plant Industry, Florida Department of Agriculture, Gainesville. 265 pp.

Hill, D.S. 1983. Agricultural Insect Pests of the Tropics and Their Control, Second Edition. Cambridge University Press; Cambridge, London, New York, New Rochelle, Melbourne, Sydney. 746 pages.

Ibrahim, A.G. 1985. The Effects of Temperature on the Development of Hemispherical Scale, Saissetia coffeae (Walker). Pertanika. 8(3): 381-386.

Le Pelley, R.H. 1968. Pests of Coffee. Longmans, Green and Co. Ltd.; London and Harlow. 590 pages.

Metcalf, R.L. 1962. Destructive and Useful Insects Their Habits and Control. McGraw-Hill Book Company; New York, San Francisco, Toronto, London. 1087 pages.

Reinert, J. A. 1974. Management of the False Oleander Scale, Pseudaulacaspis cockerelli (Cooley). Proc. Fla. State Hortic. Soc. 87: 518-520.

Valand, V.M., J.I. Patel and D.M. Mehta. 1989. Biology of brown scale 

(Saissetia coffeae) on pointed gourd (Trichosanthes dioica). Indian J. Agric. Sci. 59(9): 610-611. 

Williams, D.J. 1957. The Status of Coccus palmae Haworth and the Identity of Lecanium coffeae Walker (Coccoidea: Homoptera). Entomologist. 90: 314-315. 

Zimmerman, E.C. 1948. Saissetia hemisphaerica (Targioni-Tozzetti). 1948. In: Insects of Hawaii, Volume 5 Homoptera: Sternorhycha. University of Hawaii Press, Honolulu. 464 pages.

MAY/1993

S-COFFEA

Photos