Scale Insects

Coccoidea. Spanish: Cochinillas, coccídeos (General). Portuguese: Cochonilhas, coccídeos (Brazil).

Wax glands are especially well developed in these usually minute to small (BL 1—2 mm) homopterans and chiefly function to secrete a protective shell or covering for the insect. This takes a scalelike form in many groups. All stages and both sexes have legs with segmented tarsi tipped with a single claw.

Females are quite unlike the males in form and life-style. The latter are active, midgelike, free-living forms with one pair of wings and no feeding beak. Most, but not all, females live their entire adult lives as amorphous bags of tissue without functional legs or wings, remaining attached to their food plants by their incredibly long, hairlike feeding stylets, usually under a protective scale or interred in a hard en-crustment. They lay their eggs under or within their casements. The eggs hatch into tiny mobile crawling nymphs (crawlers) that molt and either settle down to a sessile life as females or remain active and develop into flying males.

There are several different subgroups of scale insects, each with its own structural and secretory characteristics. Female "giant scale insects" (cochinillas de cola, Margaro-didae) have well-formed legs and antennae and cover their bodies in white, waxy, overlapping plates that build up to form large (to 2 cm), hardened spheres. The insects are subterranean, feeding on roots around which they form grapelike clusters. These cystlike structures ("ground pearls") at one time were collected and made into bead necklaces in parts of the Caribbean, especially those of Margarodes formicarum (fig. 8.6d), a species first found associated with ants in the Lesser Antilles (Guilding 1830).

Llaveia axin (fig. 8.6e) is another marga-rodid type from acacias and the hog-plum tree (Spondias purpurea) in Yucatán which were used for centuries by Mesoamerican Indians. The bright orange females, each almost 3 centimeters long, were crushed and kneaded together into a wax ball that formed the base for cosmetics and medicináis and an ingredient of hard waxy finishes applied to early Mayan and Aztec pottery and gourds. Names used for this insect by natives of the area in the past include ni-in, nije, axin, oji, and tuch-cuy (Edwards 1970, Jenkins 1970).

Giant scale insects are also notoriously hardy and long lived. The published record for vitality in an insect is for specimens of Margarodes vitium that remained alive without feeding for seventeen years (Ferris 1919). The species is a pest on grapes in dry areas of South America. Apparently, this ability to lie dormant for long periods is an adaptation to dryness, the adults emerging normally after the first rains.

Other very large coccoids are the leathery "tortoise scales" (Coccidae), which have a convex shape and are covered with a thin layer of wax but no scale (BL 1—20 mm). An example is Neolecanium sallei (Wheeler 1913), found on coral trees (Erythrina) in Central America.

Included in this group are the "fluted scales," so called because of the ridged form of the wax accumulations that build up beneath the body. The most well known representative is the cottony cushion scale (Icerya purchasi; fig. 8.7a-c), a major enemy of citrus throughout America.

Female "armored scales" (escamas—Dias-pididae) typically live under a flattened, disklike scale of wax and cast nymphal skins. This is the largest and probably most injurious group, populations often exploding on their hosts; many are notorious pests of orchard and shade trees and other cultivars. Particularly bad are the California red scale (Aonidiella aurantii; fig. 8.7d) and San Jose scale (Quadraspidiotus perni-ciosus) (Marin 1987).

Mealybugs (Pseudococcidae and Eriococ-cidae) are aberrant scale insects. They are motile and without armor, being covered with a thick, crusty or flaky, white layer of wax instead. They also have long, taillike filaments projecting from the posterior (fig. 8.7f). A serious and widespread pest of pineapple is the pineapple mealybug (Dysmicoccus brevipes). Another group is the "cochineal bugs," discussed below.

Many scale insects produce copious quantities of honeydew, a source of polysaccharide for multitudes of insects near the base of food chains in ecosystems (Salas and Jirón 1977).

References

Edwards, J. G. 1970. Giant margarodid scales from Yucatán. Pan-Pacific Entomol. 46: 68. Ferris, G. F. 1919. A remarkable case of longevity in insects (Hem., Horn). Entomol. News 30: 27-28.

Guilding, L. 1830. An account oí Margarodes, a new genus of insects found in the neighborhood of ants nests. Linnaean Soc. London Trans. 9: 912-914. Jenkins, K. D. 1970. The fat-yielding coccid, Llaveia, a monophlebine of the Margaro-didae. Pan-Pacific Entomol. 46: 79-81. Marín, L. R. 1987. Biología y morfología de la "escama de San José" Quadraspidiatus perni-

Flgure 8.7 WAX BUGS, (a) Cottony cushion scale (Icerya purchasi, Coccidae), first stage nymph ("crawler"), (b) Cottony cushion scale, females, (c) Cottony cushion scale, adult male, (d) California red scale (Aonidiella aurantii, Diaspididae), female and scale, (e) Cochineal bug (Dactylopius coccus, Dactylopidae), female, (f) Longtailed mealybug (Pseudococcus longispinus, Pseudococcidae).

Salas, S., and L. F. Jirón. 1977. Simbiosis entre cochinillas de cola (Homoptera: Margaro-didae) y otros insectos. II. Estructura del sistema y significado ecológico. Brenesia 10/11: 57-64. Wheeler, W. M. 1913. A giant coccid from Guatemala. Psyche 20: 31-33.

Cochineal Bugs

Dactylopidae, Dactylopius. Spanish: Cochinillas. Portuguese: Cochonilhas. Nahuatl: Nocheztli = "prickly-pear fruit blood."

The story of cochineal is one of the most fascinating, involved, and historically important of any relating to human use of an insect product (Donkin 1977). The insect was found by the Spaniards on their first arrival in Mexico and soon exploited as a source of an intense vermilion dye that became widely known. In fact, during the early colonial period, it became the most widely traded and, next to gold and silver, the most valuable product of the Spanish Indies. The pigment, called cochinealin or carminic acid (a tetracyclic carboxylic acid or anthraquinone), is concentrated in the insect's fat body and is repugnant to ants and probably to parasites that would pretend to infect this insect (Goetz and Mein-wald 1980). The substance was thought to have medicinal value in addition to its use as a textile dye and cosmetic tint.

The name "cochineal" refers to the dye and "cochineal insect" or "cochineal bug" to the insect from which it is extracted. The latter consists of two major types, a larger, "domesticated" species (D. coccus), which shows evidence of a long association and partial dependence on human care-taking, and eight smaller "wild" and self-sufficient species, chiefly D. tomentosus. These are exposed scale insects that live openly and without protective scale coverings on the pads of Opuntia cacti, from which they suck sap.

Since earliest times in Mexico, long be fore the Conquest, the bugs have been collected, dried (grana), and processed in various ways into a dyestuff. Typically, the grana was ground into a fine powder that is soaked in hot water, to which natural acids such as citrus juice may be added (Ross 1986). The importance of the bugs is evidenced by the story in Torquemada of bags of "lice" (most certainly of dried cochineal bugs or talegas) stored in Mocte-zuma's treasure house and representing tribute from his subjects (Cowan 1865: 316f.).

Culture and harvesting was best developed in Central Mexico among the Aztecs and remained almost entirely in the hands of the Indian population (nopaleros) until very late in history. A monopoly on supply of the product was maintained by the Spanish for 250 years, but this was eventually broken by entrepreneurs anxious to profit by an industry closer to markets in Europe, India, around the Mediterranean, and even in Australia. The host was easily introduced to these areas but was followed by successful establishment of the insect only in a few places, notably, in the Canary Islands.

Evidence is strong that a similar, though less extensive, industry (from wild Dactylopius) thrived among the ancient Peruvians among whom the Quechua word macno was used for the color and its source. The historical relationships, if any, between the Mexican and South American uses of cochineal is not known.

Although its importance suffered a worldwide decline since the advent of modern synthetic dyes, cochineal has continued to be in demand in many areas of Latin America as a natural food coloring and pharmaceutical. It is even enjoying a general revival in response to the popular demand for natural substances for human consumption (Marin and Cisneros 1985, Moran 1981).

These insects, of course, are still common everywhere that Opuntia grows and are most readily recognized by the thick, stringy wax masses in which they live. These white shelters are conspicuous against the green background of the cactus pads that they may damage by their feeding- In fact, D. opuntiae has been used to control prickly pear cactus in California, India, South Africa, and elsewhere (probably the first organism used deliberately and successfully in biological control) (Moran 1981).

The insects themselves are similar to mealybugs but are smooth, with only minute surface features; they are deep, dark red and have a shiny, waxy surface. Those seen on the cacti are the nymphs (BL 2—3 mm) and adults of females (BL 4 mm), which lack wings and antennae and are bound to a small area of the plant because of their practically useless legs (fig. 8.7e). The motile, winged males are rarely observed. The minute active crawlers develop long waxy filaments, climb high on the plant, and expose themselves to the wind, which disperses them.

References

Cowan, F. 1865. Curious facts in the history of insects. Lippincott, Philadelphia. Donkin, R. A. 1977. Spanish red: An ethnogeo-graphical study of cochineal and the Opuntia cactus. Amer. Phil. Soc. Trans. 67: 1-84. Goetz, M., and J. Meinwald. 1980. Red cochineal dye (carminic acid): Its role in nature. Science 208: 1039-1042. Marín L., R. Cisneros, and F. Cisneros. 1985 [1983]. Factores que deben considerarse en la producción de la "cochinilla de carmín" Dac-tylopius coccus (Costa) en ambientes mejorados. Rev. Peruana Entomol. 26: 81-83. Moran, V. C. 1981. Belated kudos for cochineal insects. Antenna 5: 54-58. Ross, G. N. 1986. The bug in the rug. Nat. Hist. 95: 66-73.

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