At first they feed along edges of needles that arise from twigs of the previous year and later devour entire leaves on all parts of the tree. The larvae are usually gregarious unless forced to disperse due to depletion of foliage or weather conditions such as high winds or heavy rainstorms. By July or August, depending on geographic range, the larvae are usually full grown. However, a few larvae may be found as late as September. Because adults may emerge over a period of a month or more, various larval stages, cocoons and adults may be found at the same time in early summer.
Some larvae spend two or three winters within the cocoons before they pupate and emerge as adults.
However, factors may still not be sufficient to prevent outbreaks. Introduced species of parasitic wasps, such as Mesoleius tenthredinis Morley and Olesicampe benefactor Hinz. Fries, Brown and Smith and Entomophthora sp. Malathion can be used in place of Sevin, either as a wettable powder or liquid concentrate. Follow manufacturer's directions as to use.