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How to identify it
- The largest of several sawflies on ponderosa pine: mature larvae reach 24 mm. The head is brown or black and unmarked, reportedly turning red in the next-to-last larval stage; the body is greyish green with a light grey stripe down the middle of the back and a broad greenish-grey stripe on each side, with light grey, dark greenish-grey and light grey stripes lower down.[1]
- Larvae feed together in colonies on old needles. Disturbed, they raise their heads in unison in a defensive posture and may regurgitate fluid; Forest Service entomologists describe Neodiprion colonies rearing back and forth together and dabbing a droplet of pine resin at predators or parasites.[1][2]
- Eggs sit in slits cut into the edges of needles from autumn through winter, spaced less than an egg slit apart; they appear as small, evenly spaced spots of light brown discoloration along the needle.[1][2]
- Adults are small, stout, thick-waisted wasps. Neodiprion females are 8.5 to 10 mm long and males 7.5 to 8.5 mm with feathery antennae, clear wings, a shiny black body and brown to reddish-brown legs; most species look alike, and identification to species rests on females examined by a taxonomist.[2]
- Sawfly larvae resemble caterpillars but have either no abdominal prolegs or six or more pairs, while caterpillars have five or fewer.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Neodiprion autumnalis | Another ponderosa pine sawfly that overwinters as eggs. Its larvae have honey-yellow to orange heads with a distinct black eyespot and yellow to yellow-green bodies with two darker bands; N. mundus larvae are greyish green with an unmarked brown or black head.[2][1] |
| Pinyon sawfly | Feeds on pinyon pines, not ponderosa. N. mundus is recorded only from ponderosa pine.[1] |
| Red pine sawfly (Neodiprion nanulus contortae) | Also overwinters as eggs in needles, but it feeds on lodgepole as well as ponderosa pine and ranges into Alberta and Montana; N. mundus is known from British Columbia, Oregon and Idaho and feeds only on ponderosa.[2] |
| Caterpillars | Count the fleshy abdominal legs: sawfly larvae have none or six or more pairs, caterpillars five or fewer. Bacillus thuringiensis sprays for caterpillars do not work on sawflies.[1][2] |
Where it lives
Western North America. Natural Resources Canada gives the range as the southern interior of British Columbia south to California, matching its host, ponderosa pine; the Forest Service records it from British Columbia, Idaho and Oregon. Localized outbreaks were recorded in British Columbia in the Deadman River area (1946 to 1951) and along the northern arm of Okanagan Lake (1964).[1][2]
Biology and life cycle
The only host is ponderosa pine, of all ages and sizes, and the larvae eat the previous years' needles rather than the new growth.[1][2]
One generation a year. Adults emerge from late July into August and the female uses her saw-like ovipositor to cut slits into needle edges, laying eggs in late summer; the eggs overwinter, with some embryonic development probably occurring before winter.[1][2]
Larvae hatch in May and feed until late June or early July, then drop to the soil beneath the tree and spin cocoons, the females' larger than the males'. Unfertilized eggs produce males.[1]
Rain and cold while larvae are feeding, nucleopolyhedrosis virus diseases, parasitic wasps and flies, and mice, voles and invertebrates that eat cocoons all help collapse Neodiprion outbreaks.[2]
Damage and signs
Health risk
Adults resemble their bee and wasp relatives, and the female's saw-like ovipositor is used to cut egg slits in pine needles. Neither source mentions any effect on people or pets.[1]
Control
Prevention
Populations rarely cause significant damage and the sawfly never takes the new needles, so on forest and most landscape trees no treatment is needed; weigh the value of the tree against the cost before acting.[1]
Traps and physical control
On smaller landscape trees, remove the larval colonies by hand, or clip off lightly infested branches and destroy the larvae.[1][2]
Pesticides
Several chemical insecticides are effective against pine sawfly larvae when a valuable tree is heavily infested, but Bacillus thuringiensis, the biological spray for caterpillars, does not work on sawflies. Registrations change from year to year, so check current products with your county extension office or state forestry or agriculture department.[2][1]
Common questions
- Colonies of striped grey-green larvae are eating my ponderosa pine's needles. Will they kill it?
- If they are feeding on last year's needles and leaving the new shoot tips green, this is likely Neodiprion mundus, which cannot fully defoliate a tree because it never eats current-year foliage. It is common but rarely destructive.[1]
- Can I spray Bt?
- No. Bacillus thuringiensis works on moth and butterfly caterpillars, not sawfly larvae. Hand removal or clipping infested branches handles most landscape cases; several conventional insecticides work if a tree really needs it.[2][1]
- When are the eggs laid?
- In late summer. Adults fly from late July into August, and the female saws slits along needle edges for her eggs, which stay in the needles all winter and hatch in May.[1]
Sources
- Natural Resources Canada, Canadian Forest Service, “Neodiprion mundus (V.G. Nealis, revision 2025), Trees, insects, mites, and diseases of Canada's forests.” tidcf.nrcan.gc.ca/en/insects/factsheet/1000025 (accessed 2026-11-10)
- USDA Forest Service, Forest Health Protection, “Diprionid Sawflies on Lodgepole and Ponderosa Pines, Forest Insect & Disease Leaflet 179 (Ciesla and Smith, 2011).” www.fs.usda.gov/foresthealth/docs/fidls/FIDL-179-DiprionidSawflies.pdf (accessed 2026-11-10)
- iNaturalist, “Neodiprion mundus taxon page (order and family).” www.inaturalist.org/taxa/1227566 (accessed 2026-11-10)