forest, shade, ornamental, and fruit trees. Some of its most im- 
portant forest and shade tree hosts are: elm, ash, poplar, linden, 
willow, redbud, magnolia, and mountain-ash. Female scales are 
flat, circular, 1 to 2 mm. in diameter, and have a slightly raised, 
dark or yellow central area or nipple (fig. 30). Immature scales 
are small, nearly black, and have a black nipple surrounded by a 
ee ring. Male scales are oblong-oval and nearly twice as long 
as wide. 
COURTESY CONN. AGR. EXPT. STA. 
FIGURE 30.—San Jose scale, Quad- 
raspidiotus perniciosus. Note 
large number of immature 
scales. 
The winter is spent as a partly grown larva. Mature males ap- 
pear in May and mature females in June. Fertilized females give 
birth to 200 to 600 living young each. Young larvae or “crawlers” 
swarm over the tree before settling down to feed. The bark of 
heavily infested trees may be literally coated with a grayish 
crust.Male scales reach maturity in 3 to 4 weeks; the females in 
about 7 weeks. There are one to several generations per year, 
depending on locality. 
For many years after it spread over the United States, the San 
Jose scale was considered one of the most serious pests of orchard, 
shade, and ornamental trees in the country. In recent years it has 
generally been less troublesome. Two species of parasites, Pros- 
paltella perniciosa Tower and Aphelinus proelia (Walker), have 
been quite effective in its control in the Northeast. 
The walnut scale, Quadraspidiotus (=Aspidiotus) juglansregiae 
(Comstock) has a wide variety of hosts including walnut, ash, 
maple, boxelder, horsechestnut, cottonwood, buckeye, and linden. 
Female scales are flat, circular, pale grayish-brown, and about 3 
mm. in diameter. The exuvium is subcentral and reddish-brown. 
Young scales usually settle down around the female in a regular 
formation. Infestations heavy enough to kill twigs and branches 
have been observed in the South. There are two or more genera- 
tions per year. The related species, Q. forbesi (Johns), has been 
observed feeding on cherry and Q. gigas (Thiem & Gerneck) on 
poplar and willow. 
107 
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