Diprion similis
(white pine sawfly)

Pictures

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Identity

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Preferred Scientific Name

• Diprion similis (Hartig, 1834)

Preferred Common Name

• white pine sawfly

Other Scientific Names

• Diprion eremita
• Diprion simile (Hartig)
• Lophyrus eremita Thomson
• Lophyrus simile
• Lophyrus similis Hartig
• Neodiprion simile
• Neodiprion similis
• Pteronus similis (Hartig)

International Common Names

• English: imported pine sawfly; introduced pine sawfly; pine sawfly, introduced
• French: diprion importé du pin; tenthrede des coniferes; tenthrède importée du pin
• Russian: sosnovyi cherno-zheltyi pililschik

Local Common Names

• Estonia: kirju-männivaablane
• Finland: kirjotoukkamäntypistiäinen; täplämäntypistiäinen
• Germany: hornblattwespe, aehnliche kiefernbusch-; kiefernbuschhornblattwespe; weymouthskiefern-blattwespe
• Poland: borecznik podobny

EPPO code

• DIPRSI (Diprion similis)

Summary of Invasiveness

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The females of D. similis are poor fliers, therefore most of the expansion of this species in North America has resulted from the movement of infested nursery stock, trees, and foliage (Middleton, 1923; Coppel et al., 1974; Melcher and Townsend, 1999).

Taxonomic Tree

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• Domain: Eukaryota
•     Kingdom: Metazoa
•         Phylum: Arthropoda
•             Subphylum: Uniramia
•                 Class: Insecta
•                     Order: Hymenoptera
•                         Family: Diprionidae
•                             Genus: Diprion
•                                 Species: Diprion similis

Notes on Taxonomy and Nomenclature

Top of page D. similis (Hartig), the introduced pine sawfly, was first described by Hartig (1834) as Lophyrus similis. Diprion replaced the generic names Lophyrus and Pteronus [Nematus]; the second one was suppressed by the International Commission on Zoological Nomenclature (Enslin, 1916, 1917; Coppel et al., 1974).

D. similis is closely related to the common pine sawfly Diprion pini, and some authors (e.g. Konow, 1905) considered similis a synonym of pini. The striking differences in larval coloration, and differences in penis valvae and in female saw were the main evidence that D. similis is distinct from D. pini (Baer, 1906, 1916; Enslin, 1916; Monro, 1935a, Coppel et al., 1974).

A comprehensive review of D. similis, with emphasis on studies in Wisconsin, USA, was published by Coppel et al. (1974).

Description

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Eggs

The freshly laid egg is pale whitish-blue, translucent, and shiny. Just prior to hatching it becomes bluish-green to turquoise. It is oval-spheroid with parallel sides, blunt rounded ends, and a slightly convex ventral margin. When first deposited, the dimensions are approximately 0.4 x 1.4 mm and 0.5 x 1.7 mm just before hatching. The eggs are laid serially in slits cut in the edge of mature needles, and are covered by a frothy substance (Wilson, 1971; Coppel et al., 1974).

Larvae

The newly hatched larvae are 2.5 mm long, and fully grown larvae are 18 to 28 mm long. The male and female larvae have five and six feeding instars, respectively, with shiny-black head capsules. The fully grown larvae moult to the final non-feeding prepupal or pre-spinning larvae, which spin the cocoon. The body of L1 to L3 instars is uniform yellowish-green, with black thoracic legs. The L4 instar has a mottled colour pattern similar to the mature larvae. There is a double black mid-dorsal line extending the length of the body. On either side of the dorsal stripe is a yellowish stripe broken with transverse brown markings. Laterally the larva has a dark-brown to black field filled with numerous rounded yellow and white spots, many of which protrude from the surface of the body. The ventral side is pale-yellow. The body is sparsely covered with minute spines. The colours of the pre-spinning larvae are very light and pigmentation is strongly reduced.

Cocoon (pupa)

The cocoon is cylindrical with hemispherical ends. It is finely textured, somewhat glossy, and brown. The male cocoons are smaller (7.0 to 8.5 mm x 4 to 4.5 mm) than those of the females (8.5 to 10 mm x 4.5 to 5.5 mm), although there may be an overlap between the sexes. Mertins and Coppel (1972) used seed dockage sieves for the sex-separation of D. similis cocoons.

Adult

Male: 7 to 9 mm, black, abdomen ventral sometimes more or less rufous. Legs yellow, with the trochanters and basal two-thirds of the femora brownish-black. Antenna black with 22 to 24 segments, bipectinate. Penis valve: valviceps triangular, the breadth of the tip less than one-third of the base breadth.

Female: 7.5 to 10 mm, head and thorax mostly black, abdomen yellow and black. Colour pattern variable; some individuals almost dark. Legs yellow, femora partly fuscous. Antenna (including scapus) black, serrate. Lateral bands of the saw (annuli) with teeth (ctenidia) very regular and even.

 

Distribution

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D. similis is native to Eurasia, and has been introduced in northeastern North America. It occurs in central and northern Europe up to the northern parts of Fennoscandia, in Russian Siberia to the Baikal region, and in China. Since its discovery in Connecticut, USA, in 1914 (Britton 1915b), D. similis has expanded its range in the USA and Canada to cover most of the native distribution of Pinus strobus and many areas where the tree has been transplanted (Coppel et al., 1974; Melcher and Townsend, 1999). According to Drooz et al. (1979), the first reports of its presence in Virginia are incorrect. It was certainly recorded by Thomas et al. (1982).

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

History of Introduction and Spread

Top of page Coppel et al. (1974) have summarized the New World history of the introduced pine sawfly. The first discovery was made in a nursery in Connecticut in 1914 (Britton, 1915b). The sawfly was probably introduced in the cocoon stage on nursery stock imported from Holland (Rohwer, 1916). Within 10 years, Middleton (1923) recorded it from five New England states, and Indiana. The sawfly was first found in Canada at Oakville, Ontario, in 1931, and in 1933 on the island of Montreal in Quebec (Monro, 1935a). The latest new records are from North Carolina in 1977 (Doggett, 1978), Manitoba in 1982 (Wong and Tidsbury, 1983), and Kentucky in 1992 (Townsend and Collins, 1992).

Risk of Introduction

Top of page The history of the introduced pine sawfly in North America shows that this pest species may be accidentally introduced and established in new territories despite careful inspection. Apparently the cocoon stage presents the highest risk.

Habitat

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Natural stands as well as plantations, nurseries and estates are subject to infestation by D. similis. Trees of all ages are defoliated and those in the most exposed locations or in the overstorey suffer the heaviest defoliation. Ornamentals, wind break, roadside, and pasture grown trees are particularly vulnerable (Coppel et al., 1974). Infestations have also been reported from Swiss mountains over 1200 m high (Barbey, 1924; Escherich, 1942).

Habitat List

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Category	Sub-Category	Habitat	Presence	Status
Terrestrial
	Terrestrial – Managed	Cultivated / agricultural land	Present, no further details	Harmful (pest or invasive)
		Protected agriculture (e.g. glasshouse production)	Present, no further details	Harmful (pest or invasive)
		Managed forests, plantations and orchards	Present, no further details	Harmful (pest or invasive)
		Managed grasslands (grazing systems)	Present, no further details	Harmful (pest or invasive)
		Disturbed areas	Present, no further details	Harmful (pest or invasive)
		Rail / roadsides	Present, no further details	Harmful (pest or invasive)
		Urban / peri-urban areas	Present, no further details	Harmful (pest or invasive)
	Terrestrial ‑ Natural / Semi-natural	Natural forests	Present, no further details	Harmful (pest or invasive)
		Natural grasslands	Present, no further details	Harmful (pest or invasive)
		Riverbanks	Present, no further details	Harmful (pest or invasive)
		Wetlands	Present, no further details	Harmful (pest or invasive)
Littoral
		Coastal areas	Present, no further details	Harmful (pest or invasive)

Hosts/Species Affected

Top of page D. similis feeds on a number of pines (Pinus spp.). In Eurasia, the hosts include Pinus sylvestris, Pinus mugo, Pinus cembra, Pinus sibirica and the introduced Pinus strobus and Pinus contorta. In America, the preferred host is P. strobus, and common hosts include Pinus resinosa, Pinus banksiana and P. sylvestris. The host-plant associations of D. similis have been studied and reviewed by Tsao and Hodson (1956), Fogal and Kwain (1972), Coppel et al. (1974), Huber and Hain (1984), Slansky and Fogal (1985), and Codella et al. (1991).

Growth Stages

Top of page Vegetative growing stage

Symptoms

Top of page The larvae feed from May to September/October on mature needles of pines. The young larvae are gregarious, and feed in small colonies, and the older larvae disperse and are solitary. Occasionally they nibble small pits in the bark of thin branches. Light defoliation is hard to detect, moderate infestation results in thin-appearing tree crowns, and heavy outbreaks may result in the complete removal of foliage. Defoliation is always most severe and noticeable in the upper half of the crown. According to Coppel et al. (1974), the assessment of different kinds of true injuries from sawfly defoliation, especially on Pinus strobus on roadsides, is very difficult.

List of Symptoms/Signs

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Biology and Ecology

Top of page Genetics

D. similis is arrhenotokous i.e. unfertilized eggs produce haploid males. According to Maxwell (1958), D. similis has a chromosome set of seven, but Smith (1941) describes the haploid complement as having 14 metacentric chromosomes. More recent works of Rousselet et al. (1998) showed that D. similis has 14 acrocentric chromosomes (n = 14 for haploid males and 2n = 28 for diploid females).

Sex ratios reported for D. similis range from 37.5% to 59% males (Coppel et al., 1974; Craig and Mopper, 1993).

Some gynandromorphic individuals of D. similis, exhibiting characteristics of both sexes, have been reported (Britton and Zappe, 1918; Coppel, 1959; Mertins and Coppel, 1971; Martini et al., 1999), and the sexual behaviour of such individuals studied (Mertins and Coppel, 1971; Coppel et al., 1974).

Physiology and Phenology

In Europe and most of North America two complete generations occur each year, in colder climates the development is univoltine. A third generation is possible only in exceptionally favourable conditions. Winter is passed in the cocoon as eonymphal or pronymphal stages. The emergence of adults may begin in April, and continues through May and June. The adults of the second generation are in flight from July to August. The first generation larvae are present from May to August, and the second generation larvae from late July to early October. Late strugglers may succumb in the autumn before completing development. There is a great overlap in the generations, and throughout much of the growing season all stages of the insect may be found on the trees at the same time.

Reproductive Biology

The adult sawflies are ready to mate immediately after emergence. The eggs are laid serially in slits cut in the edges of mature needles. The average number of eggs per needle is six to ten with a range of one to 44. The average number of eggs laid per female is approximately 70 with a range of two to 148. All the eggs are not deposited in the same shoot or tree. Incubation time is 7 to 15 days, depending on ambient temperature.

The first three larval instars feed gregariously, but older larvae disperse and become solitary feeders. The larval feeding period lasts approximately 30 to 40 days depending on temperature. The fully grown larvae moult, producing non-feeding prespinning larvae or prepupae, which spin cocoons. The cocoons are most frequently spun on the host among the needles, at the bases of small branches, or on the trunk in bark crevices. Occasionally, they are found on non-host trees, shrubs, or grasses. In Europe, the second generation cocoons are spun beneath the tree on the ground, whereas in America those are spun, as in the first generation, above ground level.

The time spent in the cocoon depends on the length of the diapause. Non-diapausing cocoons produce adults within approximately 2 weeks. Diapause may last 4 to 5 weeks, or it may be prolonged to last 1 to 3 years or more. The causes of the induction and termination of diapause are not fully understood.

D. similis is, despite its wide distribution, a species that rarely outbreaks. One explanation for that could be that the cocoons are most often spun above ground level, and are thus exposed and vulnerable to low temperatures, predators and parasitoids.

Low winter temperature is an important natural control. Up to 50% of the larvae of the second generation are commonly killed before they reach the cocoon stage. The cocoons on trees above snow level may suffer complete mortality (Wilson, 1971).

Natural enemies

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Notes on Natural Enemies

Top of page D. similis is attacked by several hymenopterous and dipterous parasitoids; many predators, including ants, bugs, beetles, spiders, small mammals, and birds; and pathogens. The literature was reviewed by Coppel et al. (1974).

In Europe, Hardy (1939) from Poland, and Sturm (1942) from Germany published lists of parasitoids of D. similis. Coppel et al. (1974) summarized the North American records, and listed 35 species. Four of the five most important parasitoid species listed were probably of European origin and were either purposely or accidentally introduced. The most effective species in suppressing host populations are the chalcid cocoon parasitoid, Monodontomerus dentipes, and the ichneumonid larval parasitoid Exenterus amictorius. Hardy (1939) recorded the egg parasitoid Dipriocampe diprioni, in Poland.

Predation of larvae by reduviid and pentatomid heteropterans (bugs), Chrysopa spp. (Neuroptera), and numerous spider species were reported.

Many bird species are known as predators of the larvae, cocoons, or adults of D. similis. Those cocoons that remain on the trees and other objects, above the snow line, are vulnerable to attack by overwintering birds. Less than 10% of such cocoons escape destruction. Sturm (1942) reported approximately 42 to 60% predation of cocoons by birds.

Small mammals (mice, voles, shrews, chipmunks, and squirrels) destroy the cocoons of D. similis, but at a lower rate than those of diprionid species that spin cocoons in the litter or ground.

Plant Trade

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Plant parts not known to carry the pest in trade/transport
Bark
Bulbs/Tubers/Corms/Rhizomes
Flowers/Inflorescences/Cones/Calyx
Fruits (inc. pods)
Roots
Seedlings/Micropropagated plants
True seeds (inc. grain)
Wood

Wood Packaging

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Impact Summary

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Impact

Top of page In Europe, the pest status of D. similis compared to Diprion pini is a minor one. Although the two species are frequently associated in outbreaks, D. similis is rarely responsible for serious infestations. Occasional outbreaks of D. similis are known from Germany, Poland, Russia, Switzerland, and Italy, but they have seldom resulted in large-scale tree mortality (Hardy, 1939; Escherich, 1942; Sturm, 1942; Coppel et al., 1974; Casale and Currado, 1981; Pschorn-Walcher, 1982).

At the time of the introduction and discovery of the introduced pine sawfly in America, the taxonomic status of D. similis and D. pini was confused. There was great concern about the new pest, and large investigations were initiated. According to Coppel et al. (1974), the normally scattered and low populations of D. similis are seldom responsible for more than moderate defoliation in America. However, occasionally outbreak years occur resulting in severe defoliation and mortality, especially to Pinus strobus in Wisconsin and Minnesota. In Christmas tree plantations the introduced pine sawfly may cause problems, because even light defoliation renders the trees un-saleable. In general natural control factors, such as high winter mortality, parasitoids and predators have kept the population levels under an economic level.

Economic Impact

Top of page In Europe, the pest status of D. similis compared to Diprion pini is a minor one. Although the two species are frequently associated in outbreaks, D. similis is rarely responsible for serious infestations. Occasional outbreaks of D. similis are known from Germany, Poland, Russia, Switzerland, and Italy, but they have seldom resulted in large-scale tree mortality (Hardy, 1939; Escherich, 1942; Sturm, 1942; Coppel et al., 1974; Casale and Currado, 1981; Pschorn-Walcher, 1982).

At the time of the introduction and discovery of the introduced pine sawfly in America, the taxonomic status of D. similis and D. pini was confused. There was great concern about the new pest, and large investigations were initiated. According to Coppel et al. (1974), the normally scattered and low populations of D. similis are seldom responsible for more than moderate defoliation in America. However, occasionally outbreak years occur resulting in severe defoliation and mortality, especially to Pinus strobus in Wisconsin and Minnesota. In Christmas tree plantations the introduced pine sawfly may cause problems, because even light defoliation renders the trees un-saleable. In general, natural control factors, such as high winter mortality, parasitoids and predators have kept the population levels under an economic level.

Social Impact

Top of page In ornamentals and urban environments heavy defoliation of pines may be aesthetically harmful.

Detection and Inspection

Top of page All life stages (eggs, larvae, cocoons, and adults) are visible to the naked eye. Signs of defoliation and frass reveal the feeding larvae. Pheromone traps, containing the female sexual pheromone, can be used in detection and monitoring (Thomas et al., 1982; Anderbrant, 1993, 1998, 1999).

Similarities to Other Species/Conditions

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The adults of D. dimilis and Diprion pini are very similar. In D. pini males the valviceps is not clearly triangular; the breadth of its tip is more than half of the base breadth. In D. pini females the lateral bands of the saw (annuli) have teeth (ctenidia) of irregular sizes. Scapus yellow.

Prevention and Control

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Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Cultural Control and Sanitary Methods

According to Coppel and Benjamin (1965), solitary-feeding diprionid species such as D. similis and Diprion frutetorum [Gilpinia frutetorum] cannot be removed economically by hand-picking or beating and destroying methods. Ornamental or high value trees in urban areas or small pine plantations lend themselves to hand-picking. When large areas are involved, the cost factor for this type of control becomes excessive.

Host-Plant Resistance

Tsao and Hodson (1956) reported differential survival of D. similis larvae on a series of hosts on which oviposition occurred. Middleton (1923) presented a complete host list and host preference for oviposition and larval acceptance. Codella et al. (1991) found substantial between-tree variability in D. similis performance indicating a potential for resistance breeding programmes.

Biological Control

Importation and colonization of exotic and native parasitoids against pine sawflies has received considerable attention in North America. McGugan and Coppel (1962), and Coppel et al. (1974) summarized control efforts against D. similis. The releases of a European chalcid, Monodontomerus dentipes, were especially successful, although D. similis was not the prime target of introductions in North America.

Chemical Control

Diprionid sawflies are notably susceptible to most stomach and contact poisons (Coppel and Benjamin, 1965). The chemical suppression of D. similis in forested areas is generally not justified because of the relative expense, and the fact that tree mortality is rare with only loss in increment resulting from defoliation. In Christmas tree plantations or on ornamentals, even moderate defoliation may be undesirable and insecticides may be applied. The literature on applications was reviewed by Coppel et al. (1974).

Coppel and Norris (1960, 1961) reported that systemic insecticides injected into Pinus strobus gave practical levels of control of D. similis for periods up to 3 years. Parasitoids caged with foliage from injected trees were not adversely affected.

In laboratory test, pyrethroids, arylpropylethers, and acylureas were highly effective against diprionid larvae, including D. similis (Glowacka and Malinowski, 1994; Malinowski, 1995).

A Cecropia juvenile hormone applied to first-instar larvae of D. similis, caused complete mortality before the fourth-instar was reached. The effect was less on second-instar larvae, and there was no effect on the third-instar (Fogal et al., 1979).

Field Monitoring/Economic Threshold Levels

Coppel et al. (1960) and Casida et al. (1963) started investigation of the diprionid (D. similis) pheromones. The inactive precursor of the D. similis pheromone is 3,7-dimethyl-2-pentadecanol ('diprionol'). The active compound is (2S,3R,7R)-propionate, and (2S,3S,7S)-propionate is a synergist (Jewett et al., 1976; Olaifa et al., 1988). The application of sex pheromones in pest monitoring and control was reviewed by Anderbrant (1993, 1998, 1999). According to a mathematical model developed by Mertins et al. (1975), four generations of intensive trapping would theoretically be sufficient to eliminate D. similis from an isolated area.

 

References

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Anderbrant O, 1993. Pheromone biology of sawflies. Sawfly life history adaptations to woody plants [edited by Wagner, M. R.; Raffa, K. F.] San Diego, USA; Academic Press, Inc., 119-154

Anderbrant O, 1998. Monitoring pine sawflies with pheromone traps. In: Proceedings from the IUFRO WP 7.03.10 Workshop (Methodology of forest insect and disease survey in Central Europe), Ustron - Jaszowiec, Poland, 75-79.

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Coppel HC; Casida JE; Dauterman WC, 1960. Evidence for a potent sex attractant in the introduced pine sawfly, Diprion similis. Annals of the Entomological Society of America, 53:510-512.

Coppel HC; Jones PA, 1961. Pentatomid predators of the introduced pine sawfly, Diprion similis (Htg.) in Wisconsin. Entomol. Soc. Amer., Proc. North Centr. Branch 16:84-85.

Coppel HC; Mertins JW; Harris JWE, 1974. The introduced pine sawfly, Diprion similis (Hartig) (Hymenoptera: Diprionidae). A review with emphasis on studies in Wisconsin. Res. Bull. Univ. Wisc. R 2393, 74 pp.

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Coppel HC; Norris DM; Jr, 1961. Systemic insecticidal action of certain phosphates in Pinus strobus against Diprion similis. J. econ. Ent. 54 (5), (1061-2). 2 refs.

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Doggett CA, 1978. N.C. Division of Forest Resources, Forest Pest Newsletter, 20:2.

Drooz AT; Doggett CA; Coppel HC, 1979. The introduced pine sawfly [Diprion similis], a defoliator of white pine [Pinus strobus] new to North Carolina. Research Note, Southeastern Forest Experiment Station, USDA Forest Service, No. SE-273, 3 pp.; 2 pl.; 5 ref.

Enslin E, 1916. Die europäischen Diprion- (Lophyrus) –Arten. Naturw. Z. f. Forst- u. Landw., 14:1-20.

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Fogal WH; Kwain MJ, 1972. Host plant nutritive value and variable number of instars in a sawfly, Diprion similis. Israel Journal of Entomology, 7:63-72

Fogal WH; Sullivan CR; Kwain MJ, 1979. Effect of an insect growth regulator, exhibiting juvenile hormone activity, on larvae of a pine-defoliating sawfly, Diprion similis (Hartig). Report, Great Lakes Forest Research Centre, Canada, No. O-X-286, 18 pp.; 1 pl. (col.); 23 ref.

Glowacka B; Malinowski H, 1994. The activity of some acylurea insect growth regulators against forest pest sawflies (Pamphilidae and Diprionidae). Folia Forestalia Polonica. Seria A, Les^acute~nictwo, No. 36:79-90; 20 ref.

Gornas E, 1968. Stand und Problematik des gegenwSrtigen Auftretens der Kiefernbuschhornblattwespe in Polen. Archiv fnr Forstwesen, 17:641-652.

Hardy JE, 1939. Natural control of Diprion similis Htg. in Poland during 1936. Bull. ent. Res. 30 (237-46).

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Hartley EA, 1923. Parasitism of the European pine sawfly, Diprion (Lophyrus) simile Hartig, Hymenoptera, Tenthredinidae, in Pennsylvania. Journal of Economic Entomology, 16:386-388.

Hodson AC; Christensen CM, 1942. Minnesota forest insect and disease survey for 1941. Pap. Minn. agric. Exp. Sta. (Sci. J. Ser.) No. 1997 [1942?] pp. 12. [University of Minnesota.].

Huber CM; Hain FP, 1984. Oviposition and survival of the introduced pine sawfly, Diprion similis (Hymenoptera: Diprionidae), on selected conifers in North Carolina. Journal of the Georgia Entomological Society, 19(2):158-165

Jamnicky J, 1963. Diprionidae living on Pinus cembra in the Tatra National Park. Sborn. Prac Tatr. Nar. Parku, Tatr. Lomnica No. 6, (63-74). 14 refs.

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