|During summer, SPB broods develop
rapidly. Within 4-6 weeks after a tree is attacked, the new brood of adult
beetles emerges, even though tree foliage may still be green. Because of
this delay in foliage fade, many spots may already be " inactive"
(abandoned by SPB) before ground check crews can check them. Inactive spots
do not require control.
|Certain SPB spots, however, expand
in summer as adult beetles emerge from brood trees and attack pines at the
spot's edge. Continuous spot growth is most common when beetle populations
are high. From the air, the expanding spot appears as a group of red- and
yellow-crowned trees (fig. 1), and ground crews checking these spots often
find beetles in adjacent green trees. Not all spots expand after detection,
but those which do- unless controlled- may cause large timber losses