Invasive Species Compendium

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Datasheet

Diprion similis
(white pine sawfly)

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Datasheet

Diprion similis (white pine sawfly)

Summary

  • Last modified
  • 27 September 2018
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Preferred Scientific Name
  • Diprion similis
  • Preferred Common Name
  • white pine sawfly
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Arthropoda
  •       Subphylum: Uniramia
  •         Class: Insecta
  • Summary of Invasiveness
  • 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 (

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Pictures

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PictureTitleCaptionCopyright
D. similis: a final instar larva.
TitleLarva
CaptionD. similis: a final instar larva.
CopyrightMartti Varama
D. similis: a final instar larva.
LarvaD. similis: a final instar larva.Martti Varama

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.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

ChinaPresentNative Not invasive Xiao et al., 1983; Zhang and Zhou, 1996
-LiaoningPresentNative Not invasive Xiao et al., 1983; Zhang and Zhou, 1996

North America

CanadaRestricted distributionIntroduced1931 Invasive Monro, 1935a; Monro, 1935b; Coppel et al., 1974; Wong and Tidsbury, 1983
-ManitobaRestricted distributionIntroduced1982 Invasive Wong and Tidsbury, 1983
-OntarioRestricted distributionIntroduced1931 Invasive Monro, 1935a; Atwood, 1960; Coppel et al., 1974
-QuebecRestricted distributionIntroduced1933 Invasive Monro, 1935a; Coppel et al., 1974
USARestricted distributionIntroduced1914 Invasive Britton, 1915a; Rohwer, 1916; Middleton, 1923; Wilson, 1966; Wilson, 1971; Coppel et al., 1974
-ConnecticutRestricted distributionIntroduced1914 Invasive Britton, 1915a; Britton, 1915b; Britton, 1916; Rohwer, 1916; Coppel et al., 1974
-IndianaRestricted distributionIntroduced Invasive Britton and Zappe, 1918; Coppel et al., 1974
-IowaRestricted distributionIntroduced1977 Invasive Coppel et al., 1974; USDA, 1979
-KentuckyRestricted distributionIntroduced1992 Invasive Townsend and Collins, 1992; Melcher and Townsend, 1999
-MaineRestricted distributionIntroduced Invasive Coppel et al., 1974
-MassachusettsRestricted distributionIntroduced Invasive Middleton, 1923; McGugan and Coppel, 1962; Coppel et al., 1974
-MichiganRestricted distributionIntroduced Invasive Coppel et al., 1974
-MinnesotaWidespreadIntroduced1939 Invasive Hodson and Christensen, 1942; Tsao and Hodson, 1956; Coppel et al., 1974
-New HampshireWidespreadIntroduced Invasive Coppel et al., 1974
-New JerseyRestricted distributionIntroduced1916 Invasive Weiss, 1917; Britton and Zappe, 1918; Coppel et al., 1974
-New YorkRestricted distributionIntroduced1916 Invasive Britton and Zappe, 1918; Coppel et al., 1974
-North CarolinaRestricted distributionIntroduced1977 Invasive Doggett, 1978; Drooz et al., 1979; Thomas et al., 1982; Huber and Hain, 1984
-OhioRestricted distributionIntroduced Invasive Coppel et al., 1974
-PennsylvaniaRestricted distributionIntroduced1918 Invasive Hartley, 1923; Coppel et al., 1974
-Rhode IslandRestricted distributionIntroduced Invasive Coppel et al., 1974
-TennesseeRestricted distributionIntroduced Invasive Thomas et al., 1982
-VirginiaRestricted distributionIntroduced Invasive Thomas et al., 1982
-WisconsinWidespreadIntroduced1944 Invasive Coppel and Jones, 1961; Coppel et al., 1974

Europe

AustriaRestricted distributionNative Not invasive Schedl, 1975; Schedl, 1982; Liston, 1995
Czech RepublicRestricted distributionNative Not invasive Liston, 1995
Czechoslovakia (former)Restricted distributionNative Not invasive Jamnicky, 1963; Simandl, 1989; Liston, 1995
DenmarkRestricted distributionNative Not invasive Borries, 1895; Liston, 1995
EstoniaRestricted distributionNative Not invasive Viitasaari et al., 1998
FinlandRestricted distributionNative Not invasive Kangas, 1963; Viitasaari and Varama, 1987
FranceRestricted distributionNative Not invasive Liston, 1995
GermanyWidespreadNative Not invasive Sturm, 1942; Blank et al., 1998
ItalyRestricted distributionNative Not invasive Casale and Currado, 1981; Liston, 1995
LatviaPresentNative Not invasive Liston, 1995
NetherlandsRestricted distributionNative Not invasive Rohwer, 1916; Coppel et al., 1974; Liston, 1995
PolandWidespreadNative Not invasive Hardy, 1939; Gornas, 1968; Liston, 1995
RomaniaPresentNative Not invasive Scobiola-Palade, 1982; Liston, 1995
Russian FederationPresentNative Not invasive Verzhutskii, 1969; Zhelochovtsev, 1988; Zhelochovtsev, 1994; Liston, 1995
-Central RussiaPresentNative Not invasive Zhelochovtsev, 1988; Zhelochovtsev, 1994
-Northern RussiaPresentNative Not invasive Zhelochovtsev, 1988; Zhelochovtsev, 1994
-Southern RussiaPresentNative Not invasive Zhelochovtsev, 1988; Zhelochovtsev, 1994
-Western SiberiaPresentNative Not invasive Zhelochovtsev, 1988; Zhelochovtsev, 1994
SlovakiaRestricted distributionNative Not invasive Jamnicky, 1963; Liston, 1995
SwedenRestricted distributionNative Not invasive Larsson et al., 1980
SwitzerlandRestricted distributionNative Not invasive Barbey, 1924; Liston, 1995
UKRestricted distributionNative Not invasive Benson, 1951; Crooke, 1957; Bevan, 1987; Liston, 1995
UkraineRestricted distributionNative Not invasive Ermolenko, 1975; Liston, 1995

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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CategoryHabitatPresenceStatus
Littoral
Coastal areas Present, no further details Harmful (pest or invasive)
Terrestrial-managed
Cultivated / agricultural land Present, no further details Harmful (pest or invasive)
Disturbed areas 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)
Protected agriculture (e.g. glasshouse production) 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)

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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SignLife StagesType
Leaves / external feeding
Leaves / external feeding
Leaves / frass visible
Leaves / frass visible
Whole plant / plant dead; dieback
Whole plant / plant dead; dieback

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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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Adelognathus marginellus Parasite Larvae
Agrothereutes adustus Parasite Pupae
Agrothereutes mandator Parasite Pupae
Aptesis pugnax Parasite Pupae
Aptesis subguttata Parasite Pupae
Blondelia inclusa Parasite Larvae
Conidiobolus tenthredinis Pathogen
Dahlbominus fuscipennis Parasite Pupae
Delomerista pfankuchi Parasite Pupae
Dibrachys Parasite Pupae
Diplostichus janitrix Parasite Larvae
Drino gilva Parasite Larvae
Drino inconspicua Parasite Larvae
Endasys erythrogaster Parasite Pupae
Exenterus abruptorius Parasite Larvae
Exenterus adspersus Parasite Larvae
Exenterus amictorius Parasite Larvae
Exenterus oriolus Parasite Larvae
Exeristes roborator Parasite Pupae
Gelis Parasite Pupae
Gelis areator Parasite Larvae/Pupae
Gelis cursitans Parasite Pupae
Itoplectis alternans Parasite Pupae
Lamachus Parasite Larvae
Lamachus frutetorum Parasite Larvae
Lamachus ophthalmicus Parasite Larvae
Macroneura vesicularis Parasite Pupae
Mesopolobus subfumatus Parasite Pupae
Monodontomerus aereus Parasite Pupae
Monodontomerus dentipes Parasite Larvae
Monodontomerus minor Parasite Pupae
Monodontomerus strobili Parasite Pupae
Nucleopolyhedrosis virus Pathogen
Olesicampe macellator Parasite Larvae
Ophion abbreviator Parasite Pupae
Pleolophus basizonus Parasite Nymphs
Pteromalus Parasite Pupae
Rhorus substitutor Parasite Larvae
Tritneptis Parasite Pupae

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.

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Clothing, footwear and possessions Yes
Land vehicles Yes
Plants or parts of plants Yes
Soil, sand and gravelSoil; litter Yes

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Growing medium accompanying plants pupae Yes Pest or symptoms usually visible to the naked eye
Leaves eggs; larvae; pupae Yes Pest or symptoms usually visible to the naked eye
Stems (above ground)/Shoots/Trunks/Branches larvae; pupae Yes Pest or symptoms usually visible to the naked eye
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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Wood Packaging liable to carry the pest in trade/transportTimber typeUsed as packing
Solid wood packing material with bark Yes
Solid wood packing material without bark Yes
Wood Packaging not known to carry the pest in trade/transport
Loose wood packing material
Non-wood
Processed or treated wood

Impact Summary

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CategoryImpact
Animal/plant collections None
Animal/plant collections None
Animal/plant products None
Animal/plant products None
Biodiversity (generally) None
Biodiversity (generally) None
Crop production None
Crop production None
Environment (generally) Negative
Environment (generally) Negative
Fisheries / aquaculture None
Fisheries / aquaculture None
Forestry production Negative
Forestry production Negative
Human health None
Human health None
Livestock production None
Livestock production None
Native fauna None
Native fauna None
Native flora Negative
Native flora Negative
Rare/protected species None
Rare/protected species None
Tourism None
Tourism None
Trade/international relations None
Trade/international relations None
Transport/travel None
Transport/travel None

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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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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