4 CIRCULAR 920, U. S. DEPT. OF AGRICULTURE 
(Archangelskaya 1), but has not been found infested in the United States 
even when adjacent to heavily infested trees. Additional hosts recently 
reported include Pyrus, Malus, Cydonia vulgaris, and Cerasus (Borchsenius 4). 
The scale is a potentially serious pest. In addition to its weakening effect 
on the tree, the insect’s tendency to migrate to and develop on the fruit 
may Cause severe injury to some fruits. The scale causes conspicuous 
blotches on peaches (fig. 3), nectarines, and plums. When the infestation 
at Davis was discovered, it was estimated that 25 percent of the peach crop 
was damaged even though the trees had been sprayed with oil the preceding 
winter. The hulls of almonds may become heavily infested, but no damage 
to the nuts has been discovered. Although every infestation was inten- 
sively treated as soon as discovered, feasible observations suggest that the 
most important injury may result from infestation on the fruit. 
DESCRIPTION OF STAGES AND HABITS 
The Hall scale is ovoviviparous. The oval, pale-yellow crawlers are 
about 0.23 by 0.12 mm. After a short period of activity, the crawlers 
settle, insert their mouth parts into the host tissue to feed, secrete a protec- 
tive waxy covering, and gradually increase in size. The females molt 
twice and the males three times. Only the adult males have wings. 
Mating takes place soon after the females have gone through the second 
molt. 
The cover of the adult female scale is elongate-oval, about 1.08 by 0.44 
mm., and usually creamy tan with the orange exuvium of the second 
stage at one end. The body is a pale yellow. The male covering de- 
velops in the second instar as a narrow scale, with nearly parallel sides, 
thinner texture, and lighter color, whereas the female scale is more oval, 
denser, and darker. The male completes its development to winged adult 
beneath this narrow cover. 
The young scales settle on all parts of the host. Generally the males 
outnumber the females on foliage, fruit, and twigs of the current season's 
growth, but more females are present on other parts of the trees. Field 
observations indicate that the two sexes are present in nearly equal numbers. 
Many crawlers, especially the females, settle in protected places, such as 
deep crevices in wood, under loose bark, and under bud scales. This habit 
makes both inspection and control difficult. During the spring and summer 
there is also considerable movement from the trunk and larger branches to 
the current year’s twig growth, leaves, and fruit. For example, 1,812 
scales have been found on 1 almond hull and 1,962 on a current-growth 
almond twig 22 inches long. Fruits of peaches, nectarines, and prunes 
have also become heavily infested. 
The reproductive capacity of the females could not be determined from 
field observations. The maximum number of ova and embryonic cells 
observed in a single female was 74. The total progeny might well exceed 
the number of ova seen at any one time. 
SEASONAL HISTORY 
During January the only live scales found are nongravid females. A few 
gravid stages have been found in February, and most of them are gravid 
