San José scale
Diaspidiotus perniciosus (Comstock) (Hemiptera: Diaspididae)
Orientation to pest
San José scale, Diaspidiotus perniciosus (Comstock), is native to Asia (northern China, Korea, the Russian Far East) and is invasive in North America and in other temperate and subtropical areas throughout the world. It is found throughout the United States and Canada. It is a highly polyphagous species, reported from 43 different families of plants, but is economically most troublesome on members of the rose family. The scale has multiple generations per year in many areas and, if not suppressed by parasitoids, can be very damaging, killing heavily infested trees. It is not a pest in native forests, but is common on ornamental, shade, and fruit trees.
Hosts commonly attacked
Common hosts include many rosaceous plants, such as especially apple (Malus), plums and cherries (Prunus), peaches (Prunus persica (L.) Batsch), almonds (Prunus dulcis [Mill.] D.A.Webb), pear (Pyrus), and Pyracantha. Species of Malus, Prunus, Pyrus, and Pyracantha.
Distribution
This invasive species, while native to northeastern Asia, is found throughout North America, and more generally around the world in temperate and subtropical regions.
Images of San José scale
 United States National Collection of Scale Insects Photographs Archive, USDA Agricultural Research Service, Bugwood.org 768x512 |
 United States National Collection of Scale Insects Photographs Archive, USDA Agricultural Research Service, Bugwood.org 768x512 |
 United States National Collection of Scale Insects Photographs Archive, USDA Agricultural Research Service, Bugwood.org 768x512 |
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| Figure 2. Crawler of San José scale | Figure 3. Nymphs of San José scale settled around two adult females | Figure 5. View of twig infested by San José scale | |
| Figure 1. Adults (top photo) of San José scale, Quadraspidiotus perniciosus; females (bottom photo) with scale cover removed to show scale body | Figure 4. Adult male of San José scale (left); drawing of male (right) | Figure 6. Damage on apples from San José scale. Note both scales and red discoloration around scales | |
Important biological control agents related to this pest species
As San José scale moved around the world into various apple growing regions, it come in contact with local parasitoids, some of which adopted this scale as a new host. Also, several of the Asian parasitoids associated with this scale in its native range moved naturally with the scale to new regions (on apple breeding stock). Worldwide, the list of parasitoids is long and complex (see Van Driesche et al., 1996, pp. 28-31, see under web links for URL). Of these many parasitoids, the most important in North America are two North American species, Aphytis diaspidis (Howard) and Aphytis mytilaspidis (Le Baron) and two Chinese parasitoids, Encarsia perniciosi (Tower) and Coccophagoides kuwanae (Silvestri). In much of the United States, this scale is now generally held at acceptable levels by some combination of these parasitoids, unless they are absent naturally or have been suppressed by local use of pesticides.
Web links for information on San José scale
- FHTET Biological Control Bulletin | USDA Forest Service
Van Driesche et al. 1996 see pages 28-31 - Virginia Fruit Fact Sheet | Virginia Tech
- Tree Fruit IPM | Insect Identification Sheet No. 12 | Cornell University
- Orchard Pest Management Fact Sheet | Washington State University
- Pest Management Guidelines | University of California Statewide IPM Program
- Fruit Insect Focus Article | KTFREC, West Virginia University
- Species Catalog on ScaleNet
Complete list of all recorded natural enemies, hosts, and distribution records; also an index to all publications on this species - HYPP Zoology fact sheet | INRA, France
Articles
- CAB (Commonwealth Agricultural Bureaux). 1986. International Institute of Entomology, Distribution maps of pests, No. 7. Commonwealth Agricultural Bureaux, United Kingdom. [map of world distribution of San José scale]
