|Crop Knowledge Master|
Coccus hesperidum (Linnaeus)
|Soft Brown Scale|
Jayma L. Martin Kessing, Educational Specialist
Ronald F.L. Mau, Extension Entomologist
Department of Entomology
Updated by: J.M. Diez April 2007
The soft brown scale attacks a wide variety of field, ornamental and greenhouse plants. Host plants reported in Hawaii include Citrus, loquat, Moraea bicolor, Moraea iridioides, orange, orchids, papaya, rubber, and Santalum haleakalae (Zimmerman, 1948).
This scale has a cosmopolitan distribution. It has been reported in the following countries: Algeria, Australia, Austria, British Guiana, Canada, Caucasia, Chile, Cuba, Dutch East Indies, Ecuador, England, Europe, Haiti, Japan, Mauritius, Mexico, Morocco, New Zealand, Seychelles, South Africa, and West Indies (Quayle, 1941). It was first recorded in Hawaii in 1896 and is presently on all main islands.
Direct damage caused by soft scales is due to the actual feeding of the scale on the host plant. Indirect damage can occur as the growth of sooty mold associated with honeydew production.
The soft brown scale, like other soft scales, feeds from the phloem of the host plant and are be found on stems, leaves and green twigs where they are associated with veins (Copland and Ibrahim, 1985). Damage due to the feeding of an individual scale is small. However, when large populations are present yellowing, defoliation, reduction in fruit set and loss in plant vigor are caused.
Like other soft bodied insects such as aphids, leafhoppers and mealybugs, scales produce honeydew. The soft brown scale produces more honeydew than other species (Copland and Ibrahim, 1985) on the leaves and fruit of its host. This sweet and watery excrement is fed on by bees, wasps, ants and other insects which in turn may tend and offer protection to scale insects. One of the ant species to tend the soft brown scale is the Argentine ant, Iridomyrmex humilis Mayr (Timberlake, 1913). The honeydew is also the medium on which a sooty fungus grows, called sooty mold, which is the most damaging effect of this scale. Sooty mold blackens the leaf, decreases photosynthesis activity, decreases vigor and often causes disfigurement of the host. When the sooty mold occurs on fruit, it often becomes unmarketeable or of a lower grade as the fungus is difficult to wash off (Elmer and Brawner, 1975).
Infestations on Citrus usually occur near ground level, in large colonies tended by ants (Bartlett and Ewart, 1951).
Scale insects belong to one of two types, the armored scales or the soft scales. The soft brown scale is classified as a soft scale. These scales are protected by the chitinous body wall of the insect. Compared to the armored sales, they secrete very little wax. The body is usually smooth in outline, dome shaped, and brown, black or mottled in color. Soft scales retain their legs and antennae throughout adult life. Young females are primarily sedentary, but may move about for a brief time after feeding begins. Females are always wingless and males either have one pair of membranous wings or are wingless also. Although females develop eggs, they are retained within their bodies in a brood chamber.
In warmer climates and in greenhouses there are continuous generations of this scale throughout the year. In California there are 3-5 generations per year out of doors (Nakahara, 1976). In temperate areas the scale overwinters out of doors as far north as the eastern seaboard of Virginia and southern Vancouver Island.
Female soft brown scales primarily reproduce without fertilization (parthenogenesis) and birth live young. Sexual reproduction may occur in some circumstances, but the male scales are rarely found. Although the soft brown scale is slow growing, they compensate by birthing large numbers of young and if left unchecked, a few individuals can grow into very large populations (Copland and Ibrahim, 1985).
Soft brown scales are ovoviviparous in that they produce small larvae that hatch from eggs within the mother. Five to 19 eggs are laid per day over a series of 30-65 days by the adult female (Cancela da Fonseca, 1954-1956). Each female lays between 80 to 250 eggs.
The young nymphs, born within the adult female, remain in her brood chamber for a few hours before leaving. The first stage nymphs are dispersive crawlers. The crawlers search until they find a suitable spot to feed from on the plant and then settles. Movement is sluggish and they usually settle near the female. Dispersal by wind may occur during this period (Annecke, 1959). Mortality during this stage may be as high as 80% depending on the humidity and plant host (Copland and Ibrahim, 1985). Molting into the second stage occurs a few days after settling (Annecke, 1959). There are three molts, making three nymphal stages, before the scale reaches adulthood. The second and third nymphal stages are distinguished by the size of the scale. Annecke (1959) distinguishes second stage nymphs to be less than 1/12 inch long and third stage nymphs being greater than 1/12 inch. Nymphs develop into the adult stage in about 2 months at cooler temperatures (Metcalf, 1962). Reed et al. (1968) reports a minimum of 33 days at 80ûF for the development of crawler to third stage female nymph.
The adult females are characterized by a large brood chamber containing white eggs or first stage larvae (Annecke, 1959). The overall body shape is symmetrically oval, dome-like, and 1/8 to 1/6 inch long. They are pale yellowish brown to greenish and flecked with irregular brown spots. Overall color darkens as the insect ages. A detailed description is given by Zimmerman (1948). Essentially, this scale is devoid of any distinguishing features. However, the lack of features makes it readily identifiable from the scale species present in Hawaii (Zimmerman, 1948). During warmer weather, females may live for 90-125 days, producing young for 30-65 days of this period (Annecke, 1959).
Males have not been recorded for this species.
In laboratory rearing, crawlers are attracted to and move towards light (Reed, et. al., 1968). Although they are mostly sedentary after establishing a feeding site, this mite is capable of moving up until it is half grown if the leaf or twig dries or if they are disturbed (Quayle, 1941).
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).
There are over 30 known natural enemies of the soft brown scale worldwide. Parasites and hyperparasites (parasites of the parasites) are generally small flies and wasps that deposit their eggs into the scale. Parasites are known for all scale developmental stages. In some species, several parasites may emerge from one scale. Parasites present in Hawaii are Aphycus alberti Howard and Anicetus annulatus Timberlake (Zimmerman, 1948). Predators of the soft brown scale include ladybird beetles and lacewings (Hart, et. al., 1966).
Populations of soft brown scale are normally controlled by natural enemies. In some cases, these scales are controlled by indigenous parasite populations. When needed, release of reared parasites has been highly effective. Hart (1972) reported that releases of Microterys flavus (Howard) in Texas citrus groves gave longer periods of control than chemically treated areas.
Like some other scales, the soft brown scales are able to encapsulate the eggs of its parasites. Encapsulation may considerably influence the degree of biological control of parasites imported against indigenous hosts (van den Bosch, 1964) as it may hamper or prevent the establishment of introduced natural enemies in new regions (Blumberg, 1977). A study by Blumberg (1977) in Israel reported high encapsulation rates of two imported parasitoids and relatively low rates against the local parasite. Similar results were reported by Reed et al.. (1968) using two imported and one indigenous parasite in Texas. No encapsulations of parasite eggs have been reported in Hawaii.
Tending by ants hampers parasite activity in some parasite species that are slower at depositing their eggs, however control is usually reached over a considerable period (Bartlett and Ewart, 1951). Parasites with rapid egg delivery have little problems with ants.
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). As in the use of all chemicals, consult the label to see what chemicals may be used on specific crops.
Diazinon, dimethoate, and malathion are not labelled as of April 2007.
Sprays are effective on the nymphal stages of scales. However, control is difficult on other life stages. Adults are firmly attached to the plant and remain so after their death that may give a false impression of the pest status (Copland and Ibrahim, 1985). Plant sensitivity to chemical sprays may also be a factor since scales are often pests of sensitive ornamental plants (Copland and Ibrahim, 1985).
Chemical applications should be used only when parasites are not economically effective. The application of pesticides may offset control by natural enemies and present other problems in the future. Population explosions of this scale have been reported in California (Bartlett and Ewart, 1951; Elmer, et. al., 1951; Elmer and Brawner, 1975) and South Africa (Annecke, 1959) due to parathion spraying and in Texas (Hart, et. al., 1966) due to methyl parathion. Elmer and Brawner (1975) identified the elimination of the major parasite, Metaphycus luteolus (Timberlake) as the primary reason for the scale increase. Bartlett and Ewart (1951) attributed the population increase in soft brown scale to the resistance of the scale to parathion and the high susceptibility of the parasite. The stimulation in fecundity of the soft brown scale combined with the reduction of parasites and predators is reported by Hart and Ingle (1971) with the use of methyl parathion.
Annecke, D. P. 1959. The Effect of Parathion and Ants on Coccus hesperidum L. (Coccidae: Homoptera) and its Natural Enemies. J. Entomol. Soc. South Africa. 22: 245-274.
Bartlett, B. R. and W. H. Ewart. 1951. Effect of Parathion on Parasites of Coccus hesperidum L. J. Econ. Entomol. 44: 344-347.
Blumberg, D. 1977. Encapsulation of Parasitoid Eggs in Soft Scales (Homoptera: Coccidae). Ecological Ent. 2: 185-192.
Cancela da Fonseca, J. 1954-1956. Contribuicao para o estudo do Coccus hesperidum L. II. Subsidios para o estudo da sua biologia e ecologia. Broteria. 50(2-3): 53-93; 51(1): 38-51; 51(4): 161-173; 52(1): 19-35.
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. N. W. Hussey and N. Scopes. Cornell University Press; Ithaca, New York.
Elmer, H. S. and O. L. Brawner. 1975. Control of Brown Soft Scale in Central Valley. Citrograph. 60(11): 402-403.
Elmer, H. S., W. H. Ewart and G. E. Carman. 1951. Abnormal Increase of Coccus hesperidum in Citrus Groves Treated with Parathion. J. Econ. Ent. 44(4): 593-597.
Hart, W. G., J. W. Balock, and S. J. Ingle. 1966. The Brown Soft Scale, Coccus hesperidum L., in Citrus Groves in the Rio Grande Valley. J. Rio Grande Val. Hort. Soc. 20: 69-73.
Hart, W. G. and S. J. Ingle. 1971. Increases in the Fecundity if Brown Soft Scale Exposed to Methyl Parathion. J. Econ. Entomol. 64: 204-208.
Hart, W. G. 1972. Compensatory Releases of Microterys flavus as a Biological Control Agent Against Brown Soft Scale. Environ. Ent. 1: 414-419.
Nakahara, S. 1976. Brown Soft Scale - Coccus hesperidum Linnaeus. pp. 93-94. In: Syllabus for Workshop on Scale Insect Identification. Presented at the National Meeting of the Entomological Society of America in Hawaii. 115 pages.
Reed, D. K., W. G. Hart and S. J. Ingle. 1968. Laboratory rearing of Brown Soft Scale and Its Hymenopterous Parasites. Ann. Ent. Soc. Am. 61(6): 1443-1446.
Timberlake, P. H. 1913. Preliminary report on the parasites of Coccus heperidum in California. J. Econ. Entomol. 6(3): 293-303.
Quayle, H. J. 1941. Soft Brown Scale Coccus hesperidum Linn. pp. 96-101. In: Insects on Citrus and other Subtropical Fruits. Comstock Publishing Co. Inc., Ithaca, New York.
Zimmerman, E. C. 1948. Coccus hesperidum Linnaeus pp. 301, 304-306. In: Insects of Hawaii. A Manual of the Insects of the Hawaiian Islands, including Enumeration of the Species and Notes on Their Origin, Distribution, Hosts, Parasites, etc. Volume 5. Homoptera: Sternorhyncha. 464 pages.