The pinyon pine sawfly, Neodiprion edulicolus Ross, has periodically caused serious defoliation of singleleaf pinyon, Pinus monophylla Torr. and Frem., in the Intermountain Region. Infestations have been short-lived, however, and widespread tree mortality has not been known to occur.
The first recorded outbreak of N. edulicolus in the Intermountain Region was detected in 1959 along Nores Truck Road near Pioche, Nevada. Mortality of smaller trees occurred. Population levels were low in 1962, 1963, and 1964.
Over 100,000 acres of pinyon pine in the same general area near Pioche and near Caliente, Nevada, were heavily defoliated in 1965 and 1966. Most of the pinyon were rendered unfit for sale as Christmas trees.
The life cycle and stages are typical of Neodiprion species. Eggs overwinter in pinyon needles; eclosion commences in April and is completed by mid-May. Feeding larvae develop through four to six instars; ultimate instars drop to the ground and spin cocoons underneath duff and in sandy soil beneath the host trees in June. Prepupae spend the summer in the cocoon, pupate in the fall, and adults emerge in October and November to mate and oviposit.
Unfavorable climatic factors, followed by heavy parasitism of the remaining larvae, reduced the sawfly population to a low level near Pioche in 1960, and near Caliente in 1966.