Cochineal scales—Dactylopius spp.
At least three cochineal scale (Dactylopiidae) species occur in California. These sucking insects feed only on cacti, usually on prickly pear (Nopalea, Opuntia, and Platyopuntia spp.). Scale presence is undesirable on prickly pears planted as drought-tolerant ornamentals and thorny living fences and for their edible fruit and pads.
Identification
Settled stages of Dactylopius spp. have a bright red body. Adult females are 1/16 to 1/4 inch long. Except for the pinkish crawlers and adult males, cochineal scales are immobile and covered with pale, sticky, wax. Their red color often is not visible unless the body cover is pierced. The delicate adult males have one pair of wings and two long thin tail filaments.
California cochineal scale, Dactylopius confusus, females are imbedded in more profuse white wax secretions than the other Dactylopius spp. Once settled and feeding, it generally is not possible to distinguish one individual California cochineal scale from another.
Opuntia cochineal scale, D. opuntiae, usually occurs in groups around the bases of prickly pear spines. The white covers secreted by each female are separate.
Tomentose cochineal scale, D. tomentosus, produces much less wax than the other California species. Its wax is more transparent and consists of relatively straight filaments. The body of settled tomentose cochineal scales generally is visible through the wax filaments.
Similar-looking species include the cactus spine scale, Acanthococcus coccineus, and A. dubius. Both Acanthococcus spp. form white egg sacs on cactus, which resemble the white covers of Dactylopius.
The cactus mealybug, Spilococcus mamillariae, also forms white egg sacs on cactus. Its body fluid color is gray rather than bright red.
The spinose mealybug, Hypogeococcus spinosus, resembles Dactylopius spp. It has a reddish body, but it is not as bright red. Spinose mealybug is seldom encountered in California outside of plant nurseries.
Life cycle
All species of Dactylopius have several generations per year. Female scales develop through three life stages (instars). Males have five instars.
Female cochineal scales lay eggs, which hatch into mobile first instars (crawlers), each less than 1/25 inch long. Female crawlers are covered with elongate, stiff bristles that enable the insects to disperse on the wind. Once settled, females feed in the same place for the rest of their life and secrete wax that covers the body. Females molt (shed their skin) twice, and after the second molt are mature and ready to mate. Each mated female can lay hundreds of eggs over a period of several weeks.
Male crawlers have fewer and shorter bristles than females, but can be wind dispersed. The immature males spend several days feeding and moving on the plant before secreting a waxy, open-ended, hollow cocoon. Inside the cocoon, the male molts into a stage sometimes called a pupa, although scale insects do not have a true pupal stage. Males then molt into a winged adult, which leaves the cocoon and flies to find a female to mate. Adult males live only a few days and do not feed.
Damage
Cochineal scales when abundant can stunt the growth of prickly pear and cause chlorosis where they feed in groups. In addition to their fouling of plants with sticky wax and the red staining when their body is squished, prolonged feeding by abundant cochineal scales can cause severe decline and eventually the death of prickly pear.
Solutions
If a plant is heavily colonized by cochineal scales, you can
- prune off and discard the most damaged pads,
- use a forceful spray of water to wash away scales' waxy covering, and
- spray insecticidal soap on the exposed scale bodies.
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Beneficial uses of cochineal scales
Cochineal scales have been deliberately introduced in locations around the world.
Biological control of weedy cacti. These scales help to biologically control introduced prickly pear. These cacti are undesirable where they displace forage plants needed for livestock and wildlife. At least four Dactylopius spp. were introduced into South Africa (PDF) to control invasive cacti. The opuntia cochineal scale was introduced on Santa Cruz Island, California, to control prickly pear that outcompete native vegetation needed by desirable wildlife.
Natural dye. In Mexico and South America, the cochineal insect, Dactylopius coccus, has been cultured for centuries as the source of the bright red carmine dye. The cochineal industry was lucrative for several hundred years and peaked around 1876, when as much as 7 million pounds of cochineal were produced.
The development of synthetic (petroleum-derived), aniline dyes caused a dramatic decline in cochineal production. Subsequent concern that synthetic red dyes may pose health human health hazards have renewed interest in cochineal scale production. Cochineal insects are still cultured for their carmine dye in the Canary Islands, Mexico, and Peru.
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For additional information, consult the Pest Notes: Scales and The Scale Insects of California Part 2: The Minor Families.
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Cochineal scales on prickly pear
Opuntia cochineal scales
Tomentose cochineal scales
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