San Jose scale, Quadraspidiotus perniciosus (Comstock) (Homoptera: Diaspididae). Photo by C. L. Cole.
Common Name: San Jose scale
Scientific Name: Quadraspidiotus perniciosus (Comstock)
Order: Homoptera
Description: Female scale insects are tiny, orange, sac-like insects beneath 1/16 inch diameter, circular, gray, waxy coverings marked with concentric rings surrounding a central, raised nipple. Male scale insects have smaller, 1/25 inch long oval coverings with a circular, raised dot located near one end.
Life Cycle: Intermediate. Mature females and immature (second nymphal instar) stages survive the winter. Rather than eggs, female scale insects produce tiny six-legged, mobile, yellow-colored young, called “crawlers.” This stage spreads the infestation to new areas on the host plant, including bark, leaves and fruit, and to new hosts. After inserting their thread-like mouthparts into the plant and feeding for 2 to 3 days, female crawlers secrete their initial scale coverings and never move from that spot. Males develop into 2-winged adults in 2 or 3 weeks and emerge from their scales to seek females to mate. Up to six generations may be produced annually. All stages of development can occur throughout the year except during the winter.
Habitat and Food Source(s): Host plants include apple, pear, peach, plums, Osage orange, other fruit trees, shrubs and shade trees. Populations of this scale insect can develop rapidly.
Pest Status: A major pest of citrus and stone fruits in Texas; medically harmless.
Damage: The first signs of infestation include a decline of tree vigor, leaf drop and appearance of sparse yellow foliage, particularly on the terminal growth. Reddish spots on the underside of bark and around scales on leaves or fruit result from feeding of immature stages. In severe cases, the entire surface of bark can become covered with layers of overlapping grayish scales. Cracking and bleeding of limbs occur and heavily injured trees may die.
For additional information, contact your local Texas A&M AgriLife Extension Service agent or search for other state Extension offices.
Literature: Metcalf et al. 1962; Thomas et al. 1972.