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How to identify it
- Mature larvae are 17 to 25 mm (0.7 to 1 inch) long with eight pairs of prolegs, a honey-yellow to orange head capsule with a distinct black eyespot, and a yellow to yellow-green body with two darker lengthwise bands. Larvae of N. fulviceps and N. ventralis share this coloring; N. autumnalis and the closely related N. fulviceps are separated mainly by their life cycles.[1]
- Larvae feed in colonies until nearly mature; when disturbed they rear their heads back and forth in unison and bring up a droplet of pine resin to dab on a predator or parasite. Young larvae eat only the needle cortex and leave the midrib; older larvae eat whole needles, and mature larvae often feed singly or in pairs.[1]
- Eggs are small, white or pale yellow-green and ovoid, set in niches in the upper surface of the needles at even spacing, where they show as spots of light brown discoloration. They are present from fall through winter.[1]
- The first sign of an infestation is crown thinning as the old foliage disappears, with frass pellets collecting under heavily fed trees. In heavy infestations the mature larvae also clip the current year's needles.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Red pine sawfly | Its western subspecies shares lodgepole and ponderosa pine and also overwinters as eggs, but its mature larvae have shiny black heads; N. autumnalis larvae have honey-yellow to orange heads with a black eyespot.[1] |
| Pine sawflies | Of the seven Neodiprion species on lodgepole and ponderosa pine, N. autumnalis is the most widely distributed, emerges as an adult in fall, and overwinters as an egg; some of the others, such as N. burkei and N. fulviceps, winter in cocoons and emerge in spring.[1] |
| Redheaded pine sawfly | N. autumnalis is a western species of ponderosa pine whose larvae have honey-yellow to orange heads with a black eyespot and two darker bands on a yellow to yellow-green body.[1] |
Where it lives
Arizona, California, Colorado, Idaho, Kansas, Montana, Nebraska, Nevada, New Mexico, Oregon, South Dakota and Washington, extending east to western South Dakota, western Nebraska, Colorado, western Kansas and New Mexico, and throughout the pine-growing regions of Mexico. Outbreaks have occurred in the ponderosa pine-grassland transition zones of east-central Colorado and north-central Arizona.[1]
Biology and life cycle
The host is ponderosa pine, and in Mexico several Mexican pines. Like other Neodiprion, the larvae feed almost exclusively on old foliage.[1]
There is one generation a year. Adults emerge in late summer or fall and the female saws individual egg niches into the needle edges, the number per needle depending partly on needle length. The eggs overwinter and hatch the following spring; larvae can feed until late summer, then drop to the duff and upper soil to spin brown to red-brown cocoons 7 to 10 mm long, the female cocoons larger. Some prepupae stay in extended diapause.[1]
Water stress in the host changes the insect's success. In Arizona cage trials, larvae on root-trenched, drought-stressed ponderosa pines clipped and rejected more foliage, ate more needles, weighed less as pupae, survived less well and fed longer than larvae on watered or untreated trees. Stress on the trees raised late-season egg laying by N. autumnalis but did not change larval development or survival, and the researchers judged that stress alone could not explain outbreaks.[2][3]
Rain and cold while larvae are feeding, nucleopolyhedrosis virus diseases, parasitic wasps and flies, and mice, voles and invertebrates that eat cocoons all help end outbreaks.[1]
Damage and signs
- Outbreaks strip the older needles almost completely and on many trees the mature larvae clip the current year's needles too. Widely spaced trees growing on dry sites with poor soils are the most heavily damaged.[1]
- Sawfly outbreaks reduce growth and occasionally kill trees, sometimes with bark beetles finishing the weakened ones. They are short, usually two to four years, and most frequent on poor sites, outwash plains and shallow infertile soils, and in open-grown stands or even-aged plantations.[1]
- In the early 1990s outbreaks covered 3,500 acres in western South Dakota and 84,000 acres in eastern Wyoming.[1]
Health risk
None of the sources mention any effect on people or pets; the larvae's defense is a droplet of regurgitated pine resin aimed at predators and parasites.[1]
Control
Prevention
Outbreaks are short-lived and end on their own as weather, virus disease, parasites and cocoon predators catch up; the sites most at risk are open-grown, widely spaced pines on dry, poor soils.[1]
Traps and physical control
Light infestations on ornamental pines can be removed by clipping off the infested branches and destroying the larvae.[1]
Pesticides
Several chemical insecticides applied from the ground or air are effective, but Bacillus thuringiensis, the caterpillar insecticide, does not work on sawflies. Private landowners can get current registered products from county extension offices or state forestry and agriculture departments.[1]
Common questions
- Is Neodiprion autumnalis the same as the ponderosa pine sawfly I read about?
- Several Neodiprion species feed on ponderosa pine and none has a widely used common name; N. autumnalis is the most wide-ranging of them. It is told from the look-alike N. fulviceps mainly by timing: autumnalis adults fly in fall and the eggs overwinter, while fulviceps winters in a cocoon and lays in spring.[1]
- Why are the larvae rearing up and spitting?
- Disturbed Neodiprion larvae rear their heads in unison and regurgitate a droplet of pine resin to smear on predators and parasites. It is a defense, not a threat to people.[1]
- Can I use Bt on them?
- No. Bacillus thuringiensis works on moth and butterfly caterpillars, not sawfly larvae. Clip out infested branches on small trees, or ask extension which registered insecticides are effective.[1]
Sources
- USDA Forest Service, “Diprionid Sawflies on Lodgepole and Ponderosa Pines, Forest Insect and Disease Leaflet 179 (Ciesla and Smith, January 2011).” www.fs.usda.gov/foresthealth/docs/fidls/FIDL-179-DiprionidSawflies.pdf (accessed 2026-11-10)
- Oecologia (Springer), “Influence of watering and trenching ponderosa pine on a pine sawfly (D.G. McCullough and M.R. Wagner, Oecologia 71:382-387, 1987) (abstract).” doi.org/10.1007/BF00378711 (accessed 2026-11-10)
- Oecologia (Springer), “Influence of induced water stress in ponderosa pine on pine sawflies (M.R. Wagner and D.P. Frantz, Oecologia 83:452-457, 1990) (abstract).” doi.org/10.1007/BF00317194 (accessed 2026-11-10)
- iNaturalist, “Neodiprion autumnalis taxon page (order and family).” www.inaturalist.org/taxa/783994 (accessed 2026-11-10)