Pine sawflies affecting ponderosa pine have been active in several locations since 2007. Notable outbreaks have been observed on the Apache-Sitgreaves National Forests (visible along Highway 260 between Pinedale and Overgaard), Kendrick Mountain on the Coconino and Kaibab National Forests, and on San Carlos tribal lands. A new outbreak affecting an estimated 700 acres was observed in the Zuni Mountains of the Cibola National Forest in late 2009. While primarily damaging ponderosa pine, feeding was also observed on a few piñon within this area.
Sawflies are relatives of wasps and bees. These insects generally have only one generation per year. Sawfly infestations can cause temporary tree growth loss and sometimes tree mortality, especially when the trees are already stressed or the defoliation continues into a second year. Often the larvae feed in groups. On landscape trees, homeowners are encouraged to keep their trees healthy by deep infrequent watering during dry spells. Caterpillars can also be removed from the trees with a strong jet of water.