Emerges the same season and must find an alternate host in which to overwinter

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emerges the same season and must find an alternate host in which to overwinter.

Omotoma contains one described species, 0. fumiferanae (Tothill) (Stone et al. 1965). It occurs from coast to coast on various Geometridae, Noctuidae, and Tortricidae. In the West it is an important parasite of Choristoneura occidentalis (Carolin and Coulter 1959). The adult fly deposits a large, flattened white egg on the skin of the host larva. The maggot develops within the egg and penetrates the host as it becomes a pupa. The full- grown maggot issues from the host pupa, drops to the ground, and pupates in the soil, where it overwinters. There is one gener- ation a year.

The genus Tachinomyia (Webber 1941) contains 10 species of moderately large flies that parasitize lepidopterous larvae. The abdomen of the adult male is decidedly elongate ; that of the female shorter and stouter. T. similis (Williston) is a western species that parasitizes Orgyia vetusta, Halisidota argentata, and Leucoma salicis.

Winthemia (Reinhard 1931) contains 24 species in North America, of which several commonly parasitize larvae of forest Lepidoptera. The adults have densely hairy eyes and frequently red markings on the abdomen, hence they sometimes are called "red-tailed tachinids."


The Hymenoptera (Muesebeck et al. 1951-67), with about 15,000 species in North America, is outnumbered in this area only by the Coleoptera and Diptera. Some Hymenoptera are in the front ranks of forest pests. Others are among the most beneficial insects in the forest. There are two suborders, the Symphyta and the Apocrita.


The suborder Symphyta comprises the sawflies and horntails, among which are the principal forest pests in the Hymenoptera. In this suborder, the abdomen of the adult is broadly joined to the thorax and the ovipositor is sawlike for laying eggs in plant tissue.

There are three superfamilies in the Symphyta—Megalodontoi- dea, containing the sawfiy families Pamphiliidae and Xyelidae ; Tenthredinoidea, containing all other sawflies ; and Siricoidea, containing the horntails and their relatives.



This family contains four genera in North America. A can­tholyda [Itycorsia] and Cephalcia (Eidt 1969, Middlekauff 1958) feed upon conifers. Neurotoma and Pamphilius feed on broad-leaved plants. Most pamphilids are of little importance, but some of the conifer-infesting species are pests of ornamental trees, and some are considered potentially important in forest plantations.

The adults have long, slender, many-segmented antennae. The larvae (figs. 253B, 254A) resemble larvae of the free-feeding saw-flies, but differ in having a pair of three-segmented appendages on the last segment of the body and by not having any leglike appendages on the abdomen. The larvae feed gregariously or singly. The gregarious ones, sometimes called false webworms, spin and feed in silken nests which become filled with discarded food, cast skins, and frass (fig. 253A). The solitary ones build silk-tube shelters along the branchlets (fig. 254B). The nesting habit of the larvae and their wrinkled, rear-tapered appearance aid identification. Pupation is in an earthen cell in the ground. There is one generation per year, but diapause for 2 or more years is common.

Acantholyda contains about 20 species in the West (Middle­kauff 1958). Some are gregarious ; others are solitary. Acan­tholyda burkei Middlekauff and A. verticalis (Cresson) are con 

F-523502, F-523503

FIGURE 253.—A false webworm, Acantholyda species, on ponderosa pine:
A, Nest, showing accumulated frass; B, mature larva, 22 mm long.


F-523504, F-523505

FIGURE 254.—Solitary web-spinning sawfly, Acantholyda species, on grand fir:
A, Mature larva, 18 mm long; B, silk-tube shelter on branchlet.

sidered to be important pests of Monterey pine in California. Hosts and distribution of some of the more widely distributed species are :

A. albomarginata (Cresson) Pinus ponderosa 1 and Alaska, British Columbia,

P. muricata1 Wash., Oreg., Calif., and Mont.

A. atrata (Cresson) Tsuga heterophylla and British Columbia, Wash.,

Abies concolor Oreg., Calif., and Idaho

A. balanata (MacGillivray) Pseudotsuga menziesii, Alaska, British Colum 

Picea sitchensis, Abies, bia, and Calif.

and Tsuga

A. brunnicans (Norton) Pinus contorta,1 P. British Columbia, Oreg., sabiniana,' P. ponderosa,' Calif., Mont., Wyo., and

and P. radiata 1 Nev.

A. bucephala (Cresson) Pseudotsuga menziesii British Columbia, Wash.,

and Abies concolor Oreg., Calif., and Mont.,

A. burkei Middlekauff Pinus radiata Calif.

A. verticalis (Cresson) Pinus radiata, P. con- British Columbia, Alberta,

torta,' P. ponderosa,' Wash., Oreg., Calif.,

and P. monticola' Mont., Wyo., Colo., and Nebr.

1Recorded as a probable host.


Species Hosts Distribution

Cephalcia contains 10 species in North America (Eidt 1969) . C. californica Middlekauff and C. hopkinsi (Rohwer) are west­ern; C. provancheri (Huard) and C. fascipennis (Cresson) are transcontinental. The eggs are laid on the needles with a small knoblike part inserted into the host tissue. C. provancheri larvae are solitary. C. californica and C. fascipennis are gregarious. These three eat the previous year's foliage and pupate in unlined cells in the soil. Little is known of C. hopkinsi. Hosts and distribu­tion of these four species are as follows :

Species Hosts Distribution

C. californica Pinus ponderosa and Calif., Mont., Wyo., and

P. contorta British Columbia

C. fascipennis Picea engelmannii, P. British Columbia glauca, and P. pungens

C. hopkinsi Pinus ponderosa Ariz.

C. provancheri Picea engelmannii, P. Alaska, Yukon Territory,

glauca, P. mariana, and Alberta, British Colum 

P. sitchensis bia, Idaho, Oreg., Calif., Utah, Colo., Wyo., Man­itoba, and Saskatchewan


The Xyelidae (Burdick 1961, Smith 1967a) are primitive saw-flies. Three of the five North American genera feed on western conifers. None is reported to be economically important. The adults are characterized by antennae having an elongate third segment topped by a many-segmented thread. The larvae are creamy-white, slightly curled, and with weakly developed thoracic legs and prolegs reduced to swellings.

Adult Xyela are in flight a short time. They feed on pollen of willow, alder, maple, oak, grasses, and other plants. Xyela larvae feed in staminate cones of pines. Pleroneura, and Xyelecia larvae bore in the buds and developing shoots of firs. Actual and pre­sumed hosts of western species (Burdick 1961, Smith 1964, Smith 1967b) are shown in table 16.

The larvae are often encountered but seldom identified to spe­cies because they are difficult to rear. The mature larvae of Xyela drop to the ground where they remain 2 years before pupating. During the period of larval drop, people camped under pines sometimes report an invasion of these worms.


The sawflies of this superfamily have diverse habits. Most of them feed openly on the foliage ; others feed in nests, mine in leaves, or form galls. In this superfamily the sawflies are dis­cussed alphabetically by family regardless of habit. For classifica 


tion of adults see Ross (1937), for larvae see Yuasa (1922) ; and for distribution see Benson (1962a) .

Some of the free-feeding sawflies are among the most destruc­tive forest insects. They weaken and kill trees by defoliating them. In the Eastern States and Provinces, introduced sawflies have

Table 16.—Hosts, actual and presumed, and western distribution
of species of

Species Hosts Distribution

Pleroneura brunneicornis Abies balsamea Alberta Rohwer

balsam shootboring sawfly

P. californica (Ashmead) Abies Idaho, Oreg., Calif., and Utah

P. koebelei Rohwer Unknown Oreg.

P. lutea Rohwer Unknown Oreg.

Xyela alberta (Curran) Pinus contorta Alberta, Mont., and


X. alpigena (Strobl) Unknown Colo. (= brunneiceps Rohwer)

X. bakeri Konow Pinus ponderosa and Alberta, British

P. sabiniana Columbia, Wyo., Colo., Ariz., Nev., Calif., Oreg., and Idaho

X. californica Rohwer Unknown Calif., Oreg., Idaho, and Utah

X. cheloma Burdick Pinus ponderosa British Columbia, Idaho, Wash., Oreg., Calif., and Nev.

X. concava Burdick Pinus monophylla Calif. and Nev.

X. deserti Burdick Pinus monophylla Calif.

X. linsleyi Burdick Pinus ponderosa Calif., Wash., and Idaho

X. lunata Burdick Pinus coulteri and Calif. P. sabiniana

X. minor Norton Pinus coulteri, British Columbia,

P. muricata, Wash., Idaho, Wyo.,

P. ponderosa, and Utah, Colo., Ariz.,

P. sabiniana Calif., and Oreg.

X. obscura (Strobl) Pinus ponderosa British Columbia,

(= pini Rohwer), Alberta, Northwest Territories, Wash., Idaho, Mont., Colo., and Calif.

X. priceae Burdick Pinus coulteri Calif.

X. radiatae Burdick Pinus radiata Calif.

X. serrata Burdick Pinus muricata Calif.

Xylecia nearctica Ross Abies concolor and possibly Idaho, Wash., Oreg.,

Pinus contorta and Calif.


been particularly destructive to spruce, larch, and pine. In the West, where introduced sawflies are fewer, native species occa­sionally cause extensive heavy defoliation in natural forests, kill­ing some trees and reducing the growth and vigor of others, thus subjecting them to attack by other insects. In forest plantations, on Christmas tree areas, and on ornamentals, sawflies sometimes are a persistent problem.

Adults have a thick body with the head, thorax, and base of the abdomen nearly equal in width. The wings are membranous with a conspicuous network of veins. The front pair of wings is larger and more heavily veined than the hind pair. Body color is varied but tends to match the color of bark and foliage surfaces—incon­spicuous greens, browns, and black. The adults range in length from about 6 mm to over 25 mm, with most of them being less than 12 mm. The female has a sawlike attachment at the end of the abdomen that she uses to cut slits in plant tissues in which she lays eggs.

Larvae resemble hairless caterpillars except that most of them have seven or eight pairs of leglike appendages on the abdomen. True caterpillars have fewer. The larvae of many sawflies spin capsulelike, papery cocoons in which to pupate. Some species spin their cocoons in the soil and forest litter, others on the foliage. The cocoons may aid in identification (Wong 1951). Some sawflies pupate in earthen cells in the ground.

Sawflies typically have one generation a year ; however, some of the brood of many species go into diapause in the cocoon and require 2 to several years to complete development. Sometimes a large percentage of a sawfly population goes into extended dia­pause. Another characteristic of many sawflies is that outbreaks occur sporadically at long intervals. Outbreaks usually subside quickly. Between outbreaks, populations characteristically are very low.

Many sawflies have a large complement of insect parasites. Others are decimated by disease. Those that pupate on the ground often are heavily preyed upon by small mammals.

Parasites have been imported and colonized with considerable success for biological control of introduced sawflies. Application of viruses for, control has shown promise. Chemicals for control have been applied principally in plantations and on ornamentals.


Adults of the family Argidae may be identified by their three-segmented antennae. The genus Arge contains about 12 species, mostly eastern, some of which feed on forest trees. The birch saw-fly, A. pectoralis (Leach) (Schwarz 1909), ranges westward from


the Atlantic States and Eastern Provinces to British Columbia on birch. It also feeds on alder and willow. Eggs are laid in rows in the edges of a leaf. The full-grown larva is about 20 mm long; the head is reddish yellow with black eyespots; the abdomen is yellowish with several longitudinal rows of black spots. Occasion­ally this sawfly causes conspicuous defoliation locally but it is not a serious pest. A. clavicornis (F.) is a transcontinental species of similar habits. Color of the adults is widely varied. Willow, birch, and alder are hosts.


The family Cimbicidae contains our largest sawflies. Larvae of the genus Cimbex are solitary feeders on broad-leaved trees. They are conspicuous because of their size, but are seldom abundant; hence they are of little economic importance. Two species occur in the West.

The elm sawfly, C. americana Leach, ranges west to Oregon and British Columbia. Hosts are willow, elm, poplar, alder, birch, and other broad-leaved trees. The adults are robust, about 20 mm long, and have short knobbed antennae and smoky wings. They vary in color, typical ones being steel blue to black. The typical female has three or four pairs of yellow spots on the dorsum of the abdo­men; the abdomen of the male is black. The larvae are hairless, transversely wrinkled, and yellowish to greenish white with a median black stripe down the back and black spots around the spiracles. When at rest, the larvae usually are coiled.

Adults of the elm sawfly may kill twigs by gnawing on the bark, especially in the tops of trees. Larvae feed on the leaves. Eggs are laid in the leaves. Cocoons are spun in the litter and topsoil. The winter is spent as prepupal larvae in cocoons. There is one gen­eration per year. Extended diapause is common.

Adults of the variety C. americana pacifica Cresson, which occurs on willow in the Pacific coast region, are brownish red. C. rubida Cresson, also reddish, occurs on willow in California and Nevada.

Trichiosoma adults are similar to those of Cimbex but are con­spicuously more hairy and the larvae lack the median black stripe. T. triangulum Kirby (Wong 1954), a transcontinental species, feeds on willow, poplar, alder, birch, and cherry.


The conifer sawflies, Diprionidae, include many destructive species, all but one of which feed openly on the foliage of conifers. The western species all are natives. The European spruce sawfly, Diprion hercyniae (Hartig), the introduced pine sawfly, D. similis


(Hartig) , and the European pine sawfly, Neodiprion sertif er (Geoffroy) , introduced into the Eastern States and Provinces from Europe, are potential invaders that western foresters should be alert to detect. The former now occurs in southeastern Manitoba (Wong 1972) .

The adults are 6 to 12 mm long, usually yellowish brown to black and with yellowish legs. The antennae have 13 to 26 seg­ments which are serrate in the female and plumelike in the male. The male is smaller and often darker. The full-grown larva is 18 to 25 mm long and usually is yellowish or greenish with longi­tudinal stripes. The body is cylindrical and tapers gradually to the rear. The abdomen has eight pairs of leglike appendages. Eggs are laid in pockets excavated singly or more often in rows in living needles. The young larvae feed gregariously, several to a needle, all headed outward from the twig. Older larvae wrap the rear end of the body around the needle on which they are feeding.

Augomonoctenus libocedrii Rohwer sometimes infests cones of incense-cedar in California and Oregon, causing damage resem­bling that of cone-feeding caterpillars. The adult sawflies are 6 to 10 mm long, shining blue black, with the first five segments of the abdomen brick red.

Of all the sawflies, the species of Neodiprion are of greatest concern to western foresters. Some attack young trees, particularly open-growing ones, hence are significant and increasingly im­portant pests in plantations. Others attack trees of all ages. Neodiprion sawflies may develop to outbreak numbers either locally or extensively. They feed on old foliage, generally weakening the affected trees and slowing down their growth rather than killing them outright. Teamed with insects that feed on new foliage, these sawflies are a special threat. Outbreaks typically are of short duration.

The species of Neodiprion are similar in habits and appearance. According to Ross (1955) there are about 16 species in the West, but some of them appear to be complexes of several closely related species, races, or physiological strains. Some species may be mas­querading under two or more names (Ross 1955) . Identification is correspondingly difficult and uncertain, even for taxonomists.

The females lay batches of eggs in nearby needles ; eggs are placed in niches cut into the edge of a needle, often several per needle (fig. 255A). Upon hatching, the larvae tend to feed in colonies (fig. 255B) until nearly mature, when they feed singly (fig. 255C) . Most cocoons are formed in the duff and upper layer of soil ; some are formed on foliage, bark, and other surfaces (fig. 255D) . Extended diapause is common. Male and female adults (fig. 255E and F) differ, as described for the family.



F-523506, F-519389, F-528507, COURTESY CANADIAN FORESTRY SERVICE, F-523508, F-523509

FIGURE 255.—Life stages of conifer sawflies, Neodiprion spp.: A, Egg niches on pine needles; B, small larvae, 8 mm long, feeding as a colony; C, mature larva, 18 mm long; D, cocoon, 7 mm long; E, female adult, 8 mm long; F, male adult, 6 mm long.

Normally these sawflies occur in small numbers, escaping atten- tion year after year. Occasionally some species become widely epi- demic, causing spectacular defoliation for a year or two. Outbreaks subside abruptly due to natural causes. The need for control has not been fully evaluated, but it appears that plantations, Christmas tree areas, and perhaps recreation areas are most likely to require control.

One or more undetermined species of Neodiprion commonly feed on Douglas-fir. Occasionally, as in 1960 in southern Idaho, there are conspicuous local outbreaks that quickly subside without doing much damage.

The balsam fir sawfly, Neodiprion abietis (Harris) , is reported to attack balsam fir and spruce in the East and to range west at

least to Alberta, where it is a pest of shelterbelts and ornamental plantings. There appear to be several forms or species closely related to N. abietis on Abies, Picea, Pseudotsuga, and Tsuga in the West. In California from 1951 to 1955, widely scattered out­breaks of one of these species drastically reduced growth of heavily defoliated trees and killed some suppressed trees (Struble 1957a). Epidemic populations developed in dense stands predominantly of white fir. Feeding was heaviest on understory trees and the lower parts of crowns of all infested trees. Many insect parasites and predators were associated with the sawfly in the California out­breaks, but their control effectiveness was not determined. Natural control was attributed to nucleopolyhedrosis virus. Aerial spraying was demonstrated to be effective in California but may seldom be necessary.

Adult males average 5 to 6 mm long and females 6 to 8 mm. The body color is yellowish brown to dark brown. The larvae change from dark olive green in the early instars to yellowish green at maturity. The mature larvae have two darker lateral stripes. The species in California has a 1-year life cycle and overwinters in the egg stage, except for a small percentage in diapause in the cocoon.

The lodgepole sawfly, Neodiprion burkei Middleton (Burke 1932), attacks lodgepole pine in Montana and Wyoming. During the years 1921 to 1925, this sawfly and the needletier moth were concurrently epidemic on 80,000 acres in the upper drainage of the Madison River in these two States. The sawfly prefers old foliage; the needletier prefers new foliage. In combination they killed practically all trees on 12,000 acres and severely damaged the forest on an additional 20,000 acres.

The adults are 6 to 8 mm long. The females are brownish, the males black. The mature larva is about 24 mm long, hairless and wrinkled, and greenish or grayish with lighter stripes on the sides and back. The head is dark brown. This sawfly has one generation per year, but part of each brood remains as prepupal larvae in the cocoons for 2 to 4 years. The winter is spent as prepupal larvae in the cocoons in the litter on the ground.

On the basis of the one recorded outbreak, the lodgepole sawfly is a potential economic pest. Aerial spraying should be effective, if natural controls fail.

The pinon sawfly, Neodiprion edulicolus Ross (McGregor and Sandin 1969), attacks Pinus monophylla and P. edulis. It is recorded from Colorado, New Mexico, Utah, and Nevada. In out­breaks in Nevada in 1959 and again in 1965, trees of all ages and sizes were attacked. Smaller trees were most seriously defoliated ; some were killed and many were made unfit for Christmas trees. Parasites and weather were considered to be effective in natural control. No practical method of direct control is known.


The adult female is 6 to 8 mm long, with a golden-brown body. The male is 5 to 7 mm long, with a greenish-black body. The mature feeding larva is pale green with a dark green stripe on each side and a greenish-white stripe down the back. There is one generation a year. Eggs overwinter in the needles. Feeding is complete by July. Cocoons are formed in the soil. The cocoon stage lasts from June or July to September or October. Eggs are laid in October and November in needles of the current year.

Pine-infesting sawflies resembling Neodiprion fulviceps (Cresson) are widely distributed in the West. Ponderosa, Jeffrey, sugar, western white, and Monterey pines are attacked. These sawflies may be several related species or one variable species. Their biology indicates several. The damage they cause has not been evaluated, but obviously it is considerable on trees that are completely defoliated. Natural enemies, including a variety of insect parasites and predators, seem to be generally effective.

Based on a form studied by Dahlsten (1966) in California, the female adults are 6 to 9 mm long and predominantly brownish ; males are 5 to 7 mm long and shiny black. The color and mark­ings of larvae vary by instar, the younger instars being generally dark green and the older ones having dark green and light green longitudinal stripes. The nonfeeding prepupal larva is brownish.

The sawfly studied by Dahlsten has one generation per year. Eggs are laid in October and November, averaging about 18 per needle, mostly in current foliage. The eggs overwinter. The larvae feed on foliage of the previous year or older. They mature in the spring. Cocoons are spun in the litter and soil from May to July. Pupation occurs in the fall. Duration of diapause is not recorded.

Neodiprion nanulus contortae Ross, the western form of N. nanulus, has been confused with N. burkei. Both feed on lodge-pole pine and are similar in appearance. N. nanulus contortae has been recorded in Oregon, Idaho, and Alberta. It was epidemic on lodgepole pine on pumice soils in Oregon during 1941-45 and 1952-53. Some trees were killed outright ; some were weakened and succumbed to other insects ; most recovered but were slowed in growth.

Female adults are 7 to 8 mm long and generally yellowish brown ; males are 5 to 6 mm long and predominantly black. The mature larvae are longitudinally striped, being generally olive green above and greenish white below.

In Oregon there is one generation a year. Eggs are laid in the fall and overwinter in the needles. The larvae feed on foliage of the previous year or earlier. Cocoons are spun in the litter and upper layers of soil. At times a large percentage of the larval population goes into extended diapause, spending 2 or more years in the cocoons.


The hemlock sawfly, Neodiprion tsugae Middleton (Schmiege 1970), is an important defoliator of western hemlock in the coastal forests of Oregon, Washington, British Columbia, and Alaska. It also occurs in interior forests of British Columbia, Idaho, and Montana. More than one species may be involved. Tsuga mertensiana and Abies amabilis also are recorded hosts. Extensive outbreaks on western hemlock have been recorded in natural for­ests in Oregon, British Columbia, and Alaska. The larvae feed principally on the old needles, hence tend to reduce growth rather than kill trees outright.

The adults and larvae resemble those of other Neodiprion. Characteristically, there is one generation a year, but some larvae hold over in the cocoons, taking 2 or more years to complete a life cycle. Eggs are laid in the fall and overwinter. They are laid in needles of the current year's growth, usually one per needle. Larval feeding is in the late spring and early summer. Cocoons are spun mostly in the duff but also on the needles and other surfaces.

There are many insect parasites which presumably keep this sawfly under control most of the time. Direct control measures have not been developed.

Hosts and distribution of other western species are :

Species Hosts Distribution

N. deleoni Ross Abies grandis Wash.

N. demoides Ross Pinus albicaulis Calif.

N. gillettei (Rohwer) Pinus ponderosa Colo., N. Mex., and Ariz.

N. mundus Rohwer Pinus ponderosa Calif. and Oreg.

N. pratti banksianae Rohwer Pinus banksiana Saskatchewan jack pine sawfly

N. scutellatus Rohwer Pseudotsuga menziesii Wash. and Idaho

N. ventralis Ross Pinus ponderosa Colo.

N. werneri Ross Unrecorded Ariz.

There are three species of Zadiprion, two of which feed on pines in Western United States (Smith 1971b). They resemble Neodiprion in appearance and habits. Z. rohweri (Middleton) (Brown and Eads 1967) occurs in California, Nevada, Utah, Colo­rado, and New Mexico. Hosts are Pinus monophylla and P. edulis. It is a minor pest. The larvae feed on old needles sometimes com­pletely defoliating small trees. Female adults are about 10 mm long and yellowish. Males are smaller and predominantly black. The young larvae are yellow. Mature larvae are yellowish with dark brown spots down each side. Reportedly there are two gen­erations a year except for individuals that go into diapause. Z. townsendi (Cockerell) ( = grandis (Rohwer) ) feeds on Pinus ponderosa in Nebraska, South Dakota, Utah, Colorado, Arizona,


and New Mexico. The mature larvae are nearly black except for the whitish underside. This species is a potential pest of planta­tions.


The Tenthredinidae is a large family of diverse appearance and habits (Ross 1937) . Most species feed openly. Some are leaf-miners and some are gallformers. Broad-leaved plants, including trees and shrubs, are the principal hosts. Conifers are fed upon by relatively few. One serious forest pest and several of occa­sional importance are members of this family.

The species of Anoplonyx are native sawflies that feed on larch foliage. A. canadensis Harrington and A. luteipes (Cresson) are predominantly eastern species but range westward into British Columbia and Yukon Territory. The western larch sawfly, A. occi­dens Ross and the twolined larch sawfly, A. laricivorus (Rohwer and Middleton) feed on western larch in British Columbia, Wash­ington, Idaho, and Montana. In 1921 an outbreak of the latter two species occurred extensively in larch stands of northern Idaho and western Montana. From countless numbers in 1921 the population had practically disappeared by 1922. This is the only recorded out­break of either of these sawflies. So far, they are of minor eco­nomic importance.

Adults of the western larch sawfly are black and a little less than 6 mm long. The folded wings have a blue-green metallic sheen. The larvae are about 10 mm long when full grown. The head is brown and the body is gray black with a narrow green stripe down the center of the back (Wong 1955). The larvae do their heaviest feeding from mid-July to late August. When ma­ture, the larvae leave the trees and spin cocoons in the duff. The winter is passed in the cocoon, and the new adults emerge the following spring about the time the larch foliage appears.

Adults of the twolined larch sawfly closely resemble those of the western larch sawfly, but the larvae are green with two olive stripes on each side and without a stripe down the back.

One of the four North American species of Croesus (Smith 1972) occurs in the West. The dusky birch sawfly, C. •atitarsus Norton, is common but causes little damage on Betula in Alaska, Utah, Saskatchewan, and Manitoba. The larvae are yellowish green with three dark brown spots on each body segment. They feed gregariously in S-curved posture on the edge of the leaf (Wong 1954) . Females average 9 mm long and have a black abdo­men; males average 7 mm and have a red-banded abdomen.

The alder woolly sawfly, Eriocampa ovata (L.) (Borden and Dean 1971) , is a European species now established in British Columbia on Alnus rubra. The larvae, except in the last instar,

are covered with a white, woolly secretion. They skeletonize the lower leaves on young alders. They overwinter as prepupae in cocoons in the soil. There are two generations per year.

Euura is a genus of small sawflies related to Nematus (Smith 1968). They cause closed galls on the buds, leaf petioles, and stems of willow (fig. 256). The species causing stem galls are by far the most abundant. E. exiguae E. L. Smith is very common on Salix exigua in California and probably occurs throughout the Great Basin. It causes an elongate brownish stem gall containing one to four larvae. Pupation is in the gall. Emergence and egg laying is in March and April in California. E. mucronata (Har- tig) is a circumboreal species that causes bud galls on willow from Manitoba to Alaska.

Fenusa contains three species in North America, two of which are in the West (Smith 1971a) . All three are leafminers. The birch leafminer, F. pusilla (Lepeletier) ( = pumila (Klug) ), was introduced from Europe (Friend 1933) . In the West, it is re- corded from Oregon, Washington, and Alberta as a pest of orna- mental birch. Eggs are laid on the surface of the leaf and larvae feed in the leaves causing irregular blotches which wrinkle and turn brown. Heaviest feeding is in tender foliage near the tips of branches. Similar leaf damage (fig. 257) is caused by the amber- marked birch leafminer, Prof enusa thomsoni (Konow) . This pre- sumably introduced species has spread westward into the Prairie Provinces.

Full-grown larvae of F. pusilla are flattened, about 6 mm long, white to pale green, and marked with black spots on the lower side of the thorax and the first abdominal segment. Pupation is in

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