|Crop Knowledge Master|
Pinnaspis aspidistrae (Signoret)
Victoria L. Tenbrink, Research Associate
Arnold H. Hara, Entomologist
Beaumont Research Center
Host ferns include asparagus, bird's nest, boston, elkhorn, halberd, householly, lace, leatherleaf, maidenhair, polypody, rabbit foot, resurrection, staghorn, table, and wood ferns. Fern scale also infests citrus, croton, cycads, dracaena, geranium, hibiscus, mango, orchids, coconut palm, queen palm, rhapis palm, sentry palm (Howeia) and African violet (Dekle 1965, Zimmerman 1948).
Cosmopolitan. An immigrant to the Hawaiian Islands, fern scale was first listed in 1910 (Zimmerman 1948).
The first sign of fern scales in the field is usually the presence of a mixture of male and female armor on upper and lower leaf surfaces and on stems of plants. Fern scales are small, about 1 to 2.5 mm long (1/16th to 1/8th inch). The adult female armor is semitransparent, pale brown, and oyster-shaped. The cast skin of the first instar nymph forms a spot called a terminal exuvium at one end of the armor (Dekle 1965). Male armor is about 1/2 the size of female armor, white, straight sided (not oyster-like) with three ridges running lengthwise. The terminal exuvium is pale yellow and takes up about 1/4 the length of the armor. Fern scale can be confused with a similar species with overlapping host range, P. buxi., except that males are not found in that species, whereas they are usually plentiful in fern scale infestations (Zimmerman 1948). The armor must be pried off to reveal the insect attached to the plant by hair-like mouth parts. The body is a flat, elongated oval shape without wings, legs, or eyes, Dead ones are dark brown and are dried rather than plump. Armored scales feed on plant juices and cause loss of vigor, deformation of infested plant parts, yellowish spots on leaves, loss of leaves, and even death of the plant (Dekle 1965, Beardsley & Gonzalez 1975). Since scales are spread by introduction of infested material and are difficult to identify to species outside of the lab, scales of the genus Pinnaspis are a quarantine problem on exported potted plants, cut flowers, and cut foliage.
The number of days for each developmental stage and the number of generations per year depend on temperature, humidity, and rainfall (Beardsley & Gonzalez 1975). Based on a generalized life history of other tropical species, 30 days is the approximate time to complete the life cycle from egg to reproducing adult.
Eggs are laid under the armor of the female where they develop and hatch.
The first stage after hatching is the only nymphal stage with legs, so the insects are called crawlers. Crawlers may stay under the maternal armor several hours until outside conditions, especially temperature and humidity, are good. After they leave the cover, they wander for a period ranging from minutes to days, but usually a few hours. At the end of the wandering period they flatten against the leaf or stem and begin to secrete their armor (Beardsley and Gonzalez, 1975).
Newly settled nymphs insert their piercing, sucking mouth parts into plant tissue and start feeding on plant juices. Nymphs shed their skin as they grow and develop (twice in females and 4 times in males). The cast skins, called exuviae, are incorporated into the armor at the narrow end forming a dot. Males feed only during the first and second stages, and do not enlarge their armor after that. The armor of males and females is non-living and is made of cast skins, threads, and liquid, all produced by the insect (Beardsley and Gonzalez 1975).
Female armored scales appear larvae-like. They remain under armor in one place throughout their lives to feed and reproduce. Males are protected by armor until they develop into tiny, winged adults that are very different in appearance and behavior from females.
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 & Gonzalez 1975). It is the crawler stage that can be carried directly from place to place by people, animals, birds, ants, and wind currents (Dekle 1965, Beardsley & Gonzalez 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, although the cause of this is unknown. In the last two armored stages and after emergence from the armor males do not feed. Adult males have wings, but are capable of only weak flight or wind transport. Males live only a few hours, emerging in late afternoon to mate. Mate finding is probably due to attraction to pheremones secreted by females (Beardsley & Gonzalez 1975). Because of their tiny size, short life, and evening activity, it's not likely to find adult males in the field.
Since armored scales are spread chiefly through movement of nursery stock, only propagative material that is free of scales should be planted. Adequate plant spacing is important because armored scales seldom spread from plant to plant unless the crowns of the plants are in contact (Beardsley & Gonzalez, 1975). As plants grow, pruning maintains spacing and allows maximum coverage when using insecticides.
Biological control -- Predators
Labybird beetles, or ladybugs, (Coccinellidae) have been introduced and become established in Hawaii to control armored scales. Some of these, such as Lindorus lophanthae and Orcus chalybeus, have become established on the major Islands. These beetle adults and larvae are carnivorous, eating soft-bodied insects. Scale covers that look chewed and have no insect underneath are signs that predators have been feeding on the scales.
Biological control -- Parasites
Tiny wasps lay eggs in developing scales. They are parasites that absorb food from the scale body. Instead of an adult scale under the cover, an adult wasp emerges. These can be very effective in controlling armored scales (Dekle, 1965). in Hawaii at least two wasps, Arrhenophagus albipes (Encyrtidae) and Aspidiotiphagus citrinus (Aphelinidae) parasitize armored scales.
Scraping and scrubbing to remove scales from plants are effective mechanical control tactics. Removing scales is especially important on exported plant materials, since intact armor is a sign of scale infestation
Insecticide mode of action and formulation are important because the armor covers and protects all stages but the crawler and the adult male. Contact insecticides target the crawler stage; systemics target adult females and feeding nymphs. Since scales have natural enemies, care must be taken to conserve these. Populations of other pests, such as white flies and other scales, may rise if their natural enemies are affected by chemical control. Spraying should be determined by presence of scales in the field rather than by the calendar. Scales are best detected by regularly inspecting all areas of the fields for scales. When detected, directing spray at hotspots rather than uninfested areas helps conserve natural enemies and also delay pesticide resistance
In the packing house, insecticidal soaps can be used in the cleaning water to kill crawlers while scrubbing off adults. Dipping in a soap-pyrethroid solution for five minutes is only 70% effective against adults and nymphs (Hansen et al. 1992). Even if scales are killed, it takes several days for the body to dry, so removal of the armor is required to assure inspectors that
the plant material is insect free.
Beardsley, J. W. Jr. and R. H. Gonzalez. 1975. The biology and ecology of armored scales. Annual Review of Entomology. 20: 47-73.
Dekle, G. W. 1965. Arthropods of Florida Vol. 3, Florida Armored Scale Insects. Division of Plant Industry, Florida Department of Agriculture, Gainesville. 265 pp.
Hansen, J. D., A. H. Hara and V. L. Tenbrink. 1992. Insecticidal dips for disinfesting commercial tropical cut flowers and foliage. Tropical Pest Management 38: 245-249.
Zimmerman, E. C. 1948. Insects of Hawaii Vol. 5 Homoptera: Sternorhyncha. of Hawaii Press, Honolulu. 464 pp.