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Introduced pine sawfly (Diprion similis [Hartig]) (Hymenoptera: Diprionidae)

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Introduced pine sawfly (Diprion similis [Hartig]) (Hymenoptera: Diprionidae)

United States Department of Agriculture
The Use of Classical Biological Control
to Preserve Forests in North America
The Use of Classical Biological Control to Preserve Forests in North America
Edited by Roy Van Driesche and Richard Reardon
Forest Service Morgantown, West Virginia
Forest Health Technology Enterprise Team
FHTET-2013-2 September 2014
FHTET
2013-2
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DESCRIPTION OF PEST
Taxonomy
The introduced pine sawy, Diprion similis (Hartig),
is a member of the conifer-sawy family Diprionidae
(Hymenoptera). The family contains two recognized
subfamilies, Monocteninae and Diprioninae; Diprion,
Zadiprion, Neodiprion and Gilpinia are placed in the latter
subfamily. The Palearctic genus Diprion contains ve or
six species, of which is the only species that has been
introduced into North America. Gilpinia is also a Palearctic
genus, while Zadiprion and Neodiprion, with the exception
of Neodiprion sertifer (Geoffroy), are Nearctic genera (Smith,
1979).
Distribution
Diprion similis is native to Eurasia (where it is known as the
white pine sawy) and occurs from western Siberia to the
United Kingdom, and from the Russian Federation in the
north to Italy in the south (Liston, 1995). It also has been
reported from China (Xiao et al., 1983). The sawy was rst
discovered in 1914 in North America in a nursery at New
Haven, Connecticut, (Britton, 1915), where it was probably
accidentally introduced on imported nursery or ornamental
stock (McGugan and Coppel, 1962). By 1977, it had reached
North Carolina (Drooz et al., 1979). As of October 2010,
the distribution of the sawy across the United States
included 23 northeastern states, ranging from Maine to
North Dakota in the north, south to North Carolina, and
west to Tennessee (USDA-FS, 2010). The species was rst
encountered in Canada at Oakville, Ontario, in 1931 and
in a nursery in Montreal, Quebec, in 1933 (Monro, 1935).
The sawy was recorded for the rst time in Manitoba in
1982, where it caused light to moderate defoliation of Scots
pine (Pinus sylvestris L.) (Wong, 1983). The species now also
occurs throughout the three Canadian Maritime Provinces
and into Newfoundland (NRCan, 2010).
Damage
Type The favored host of D. similis is the eastern
white pine, Pinus strobus L. (Fig. 1), but other species of Pinus
are also suitable hosts (Coppel et al., 1974). Other North
American pines reported as hosts for this sawy include
P. banksiana Lamb., P. ex il is James, P. ponderosa Lawson,
P. resinosa Ait., P. rigida Mill., P. taeda L., and P. virginiana
Mill. Eurasian hosts include P. cembra L., P. densiora Sieb. &
Zucc., P. koraiensis Sieb. & Zucc., P. mugo Turra (as montana),
P. nig ra Arnold, P. sibir ica Du Tour, P. sylvestris L., and P.
walachiana Jacks (as grifthi ). The damage to pines is caused
by larvae feeding on needles of the host plant. The sawy
is bivoltine in much of its range and consequently there are
two periods of feeding damage, one in the early summer
and a second in late summer and fall. Tree mortality can
result when a large second generation damages buds the
following year (Mertins and Coppel, 1971). The larvae feed
preferentially on the old foliage and only consume the new
foliage as it ages or after older foliage has been consumed
(Coppel et al., 1974). Although trees of all ages are attacked,
feeding is particularly severe in exposed locations and in
the overstory, where defoliation may cause branch mortality
(Mertins and Coppel, 1971). The sawy is primarily a pest
of plantations, nurseries, and ornamentals, but it is also a
serious threat to eastern white pine forests (Mertins and
Coppel, 1971).
X I P S
(Diprion similis [Hartig]) (Hymenoptera: Diprionidae)
D. Barry Lyons
Natural Resources Canada, Canadian Forest Service
1219 Queen Street East, Sault Ste. Marie, Ontario, Canada P6A 2E5
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Extent The sawy is a common pest of pines in
Europe, where it is frequently found in close association
with the congeneric species Diprion pini (L.) (McGugan
and Coppel, 1962). A review of the Forest Insect and
Disease Conditions in the United States, 1973–2005
(USDA-FS 1973-2005) revealed several infestations of the
insect. Localized outbreaks were reported in Minnesota
in 1976 and in Michigan, Wisconsin, and Vermont in
1979. The sawy was detected for the rst time in 1985
in eastern North Dakota. White pine in North Carolina
was heavily defoliated beginning in 1978, causing some
tree mortality. Lack of biological control agents and the
occurrence of three complete generations per year by
the pest were blamed for the damage. This outbreak was
the impetus for a pilot project to collect parasitoids of D.
similis in Wisconsin and release them in North Carolina. By
1981, this southern infestation had expanded from 15,540
to 25,900 km2, and also included areas in Tennessee and
Virginia. In 1983 and 1984, populations in Tennessee
and Virginia remained low but increases took place in
North Carolina. By 1986, populations in North Carolina,
Virginia and Tennessee were at low levels. Signicant
localized defoliation occurred again in North Carolina in
1989 and severe defoliation was reported over a large area
in one county in 1990. This outbreak again prompted more
parasitoid releases.
A similar review of the Annual Report of the Forest Insect
Disease Surv ey in Canada ( FIDS, 1932–1995) revealed a slowly
expanding range, characterized by localized outbreaks of
short duration. Although the sawy was rst detected in
Canada in 1931 in south central Ontario, there were no
reports of its activity from 1932 to 1939. The pest was
also detected in Montreal, Quebec, in 1940 and in Ottawa
in eastern Ontario in 1941. Slight expansion in range in
Ontario had occurred by 1948, but in 1949 there was a
dramatic increase in numbers and noticeable defoliation in
Scots pines. Slight population uctuations and expanded
distribution records occurred annually, and by 1962 the
species had reached the southern shores of Georgian Bay.
In 1970 the distribution of the insect in Ontario took two
dramatic jumps with its detection in Sault Ste. Marie in
north central Ontario and in northwestern Ontario near
Figure 1 Eastern white pines defoliated by larvae of Diprion similis. John H. Ghent, USDA Forest Service, Bugwood.org.
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1960) and was later characterized by Jewett et al. (1976).
Females (Fig. 3) are mated soon after their emergence
from the cocoon and usually begin oviposition on the
same day. Eggs (Fig. 4) are deposited sequentially in slits
cut into the edge of the host needles by the female’s saw-
like ovipositor and the exposed portion is sealed with a
glandular secretion produced by the female. The number
of eggs per needle ranged from 1 to 19, with a mean of
5.3 in Wisconsin populations. Although some females
oviposit for up to a week, most females lay the majority
of their eggs within three days. Eggs take 11 to 15 days to
hatch at ambient temperatures in the spring. In Wisconsin,
eggs appear in mid-May and larvae of the rst generation
are evident from late May until early August. Most rst-
Fort Frances. The area of defoliation of white pines in the
latter locale was approximately 388 km2 and was believed
to be an extension of the Minnesota infestation. The sawy
was detected for the rst time in the Maritime province
of Nova Scotia on eastern white pine in 1975. In 1983,
1200 ha of severe defoliation occurred on small scattered
islands in Lake-of-the-Woods in westernmost Ontario
near the Manitoba border. Moderate to severe defoliation
was detected in 1993 and 1994 along the shoreline and
on islands of Georgian Bay where mature shoreline trees
were killed, signicantly affecting the values of vacation
properties. In 1994 and 1995, seed orchards in Quebec were
being lightly defoliated by this pest.
Biology of Pest
The biology of D. similis was described by Coppel et al.
(1974) and is summarized here. Although the insect
normally is bivoltine (two generations per year), the
species varies from univoltine in some parts of Asia to
possibly trivoltine in some parts of North America. There
is considerable overlap of the generations within a growing
season. In most locations, the rst adults of the spring
generation emerge in April, with emergence continuing
through May and June. The long term sex ratio of adults
in Wisconsin was 49% males (Fig. 2), but this varied by
season, location, and year. A potent female-produced sex
pheromone was postulated for D. similis (Coppel et al.,
Figure 2 Adult male of Diprion similis. John H. Ghent,
USDA Forest Service, Bugwood.org.
Figure 3 Adult female of Diprion similis. John H. Ghent,
USDA Forest Service, Bugwood.org.
Figure 4 Eggs of Diprion similis bulging out of a needle of
the host plant. John H. Ghent, USDA Forest Service,
Bugwood.org.
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generation larvae spin their cocoons by late July, with a
few stragglers completing larval development in August.
Second generation eggs in Wisconsin are present from
mid-July to the end of August, with larvae occurring from
late July to early October with a peak in early August. At
higher ambient temperatures, second generation eggs take
seven to nine days to hatch. Females and males have six
and ve actively feeding instars, respectively, and both
sexes have an additional ultimate non-feeding instar.
Most larvae (Fig. 5) have spun cocoons (Fig. 6) by mid-
September. The larval development takes an average of
30 days in the rst generation and 38 days in the second
generation. Larvae feed gregariously in the rst to third
instars moving from the tip of the needle towards the
base. Towards the end of the third instar, larvae become
solitary feeders and disperse in search of available foliage,
even moving to other trees. The non-feeding nal instar
of D. similis is characterized by reduced pigmentation
and sclerotization. The free-living period of this stage is
less than 24 hours and ends with it spinning the cocoon.
Cocoons are generally spun on a solid object above ground
level (Fig. 6). Within the cocoon, the last instar contracts
in length and the duration of this eonymphal stage is about
two days in the rst generation and about eight months in
the overwintering generation. Thus, winter is spent as a
diapausing eonymph in the silken cocoon. The eonymph
state is followed by the pronymphal state, which lasts
about two days, wherein the pupal eyes become visible
and the terminal abdominal segments straighten out. The
pronymphal larva molts, forming the pupa. The pupal
stage lasts about seven days in Wisconsin and is terminated
by the emergence of the adult from the pupal exuvia within
the cocoon. Adults may remain quiescent for three or four
days before chewing their way out of the cocoons.
ANALYSIS OF RELATED NATIVE
INSECTS IN NORTH AMERICA
Native Insects Related to the Pest (Nontarget Species)
In North America, there are two subfamilies within the
family Diprionidae, and within each subfamily there
are two native genera: in the Monocteninae, Monoctenus
(three species) and Augomonoctenus (two species) and in
the Diprioninae, Zadiprion (two species) and Neodiprion
(33 species) (Smith, 1979). There are no native North
American species in the genera Diprion or Gilpinia.
Native Natural Enemies Aecting the Pest
Coppel et al. (1974) listed 35 species of parasitoids reared
from cocoons of D. similis based on work in Wisconsin
and literature records (Table 1). Of these species, 28 are
native to North America and have shifted to this host
from other species. Thompson et al. (1977) added a native
species to the list when they reared a single specimen of
Perilampus hyalinus Say (Hymenoptera: Perilampidae) from
Figure 5 Late-instar larva of Diprion similis. USDA Forest
Service, Region 8, Southern Archive, USDA Forest
Service, Bugwood.org.
Figure 6 Cocoons of Diprion similis. John H. Ghent, USDA
Forest Service, Bugwood.org.
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Species
Distribution by State/Province Ecological Traits as Parasitoids of D. similis
CT2MA3ON4WI5MN6NC7
Primary/
Hyperpara-
sitoid
Solitary/
Gregarious
Endoparasitoid/
Ectoparasitoid
Abundance
Order: Hymenoptera
Family: Ichneumonidae
Scambus hispae (Harris) X X P & H S En uncommon
Pimpla pedalis (Cresson) X P
Itoplectis conquistador (Say) X X X X P & H S common
Delomerista japonica (Cushman) X X X X X P S En common
Delomerista novita (Cresson) X X P S rare
Exenterus amictoriu s (Panzer)1X X X X P S common
Exenterus canadensis Provancher X X P S rare
Exenterus nigrifrons Rohwer X uncommon
Gelis tenellus (Say) X X X X P & H S Ec common
Pleolophus basizonus (Gravenhorst)1X X
Gambrus ultimus (Cresson) X P
Agrothereutes lophyri (Norton) X X X X P S Ec uncommon
Family: Eulophidae
Dahlbominus fu scipennis (Zetterstedt)1X X X P & H G Ec uncommon
Tetrastichus coerulescens Ashmead XX H S En rare
Cirrospilus avicinc tus Riley X P & H
Pediobius tarsalis (Ashmead) X X H
Elasmus apenteli Gahan X H G rare
Family: Eupelmidae
Eupelmus cyaniceps Ashmead X
Eupelmus spongipar tus Foerster1? X X X H S rare
Eupelmella vesicularis (Retzius)1X X X X P & H S Ec uncommon
Family: Perilampidae X
Perilampus hyalinu s Say X H rare
Table 1 Species of parasitoids reared from Diprion similis in North America, with distributions based on major
collections.
1 Species introduced into North America
2 CT, from Connecticut in Britton and Zappe, 1918
3 MA, from Massachusetts in Webber, 1932
4 ON, from Ontario, in Raizene, 1957; Finlayson, 1962
5 WI, from Wisconsin in Coppel et al., 1974
6 MN, from Minnesota in Weber, 1977, Thompson et al., 1977
7 NC, from North Carolina in Drooz et al., 1985
8 Introduced as Sturma inconspicua Meigen
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Species
Distribution by State/Province Ecological Traits as Parasitoids of D. similis
CT2MA3ON4WI5MN6NC7
Primary/
Hyperparasitoid
Solitary/
Gregarious
Endoparasitoid/
Ectoparasitoid Abundance
Order: Hymenoptera
Family: Pteromalidae
Amblymerus verditer (Norton) X X X X P & H G Ec uncommon
Tritneptis diprionis Gahan X
Trineptis scutellata (Muesebeck) X X P & H G uncommon
Dibrachys cavus (Walker) X X X X X P & H G Ec uncommon
Eupteromalus viridescens (Walsh) X H
Catolaccus cyanoideus Burks X H S uncommon
Habrocytus thyridopterigi s Howard X P & H G Ec uncommon
Family: Eurytomidae
Eurytoma pini Bugbee ? X ? X P S rare
Family: Chalcidae
Spilochalcis albifrons (Walsh) X P & H S rare
Order: Diptera
Family: Tachinidae
Spathimeigenia spinigera Tow ns end X P S rare
Bessa harveyi (Townsend) X X P S uncommon
Diplostichus lophyri (Townsend) X X X P S common
Euphorocera sp.
(prob. edwardsii Williston)
X P rare
Drino bohemica Mesnil1, 8 ? ?
Winthemia quadripustulata
Fabricius
X
Family: Torymidae
Monodontomerus dentipes
(Dalman)
X X X X X X P & H G Ec common
Table 1 Species of parasitoids reared from Diprion similis in North America, with distributions based on major
collections, continued.
1 Species introduced into North America
2 CT, from Connecticut in Britton and Zappe, 1918
3 MA, from Massachusetts in Webber, 1932
4 ON, from Ontario, in Raizene, 1957; Finlayson, 1962
5 WI, from Wisconsin in Coppel et al., 1974
6 MN, from Minnesota in Weber, 1977, Thompson et al., 1977
7 NC, from North Carolina in Drooz et al., 1985
8 Introduced as Sturma inconspicua Meigen
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a cocoon of D. similis in Minnesota. The parasitoid was
hyperparasitizing the exotic parasitoid Exenterus amictorius
(Panzer) (Hymenoptera: Ichneumonidae) (Fig. 7). Another
native species, Exenterus nigrifrons Rower was reported
from North Carolina (Drooz et al., 1985). No parasitoids
have emerged from egg collections in Wisconsin (Mertins
and Coppel, 1971) and none were known from the North
American literature (Coppel et al., 1974).
HISTORY OF BIOLOGICAL
CONTROL EFFORTS
Area of Origin of Insect
Introduced pine sawy is of European origin.
Areas Surveyed for Natural Enemies
During the years 1933 to 1940, almost 32 million cocoons
from eleven species of spruce or pine-feeding sawies
were collected from Europe and Japan and sent to the
Entomology Laboratory, Belleville, Ontario, to rear
parasitoids for release against Gilpinia (formerly, Diprion)
hercyniae (Hartig) in Canada (Finlayson and Finlayson,
1958). European sawy cocoons were collected from
the former Czechoslovakia, and Estonia, Hungary,
Sweden, Germany, Netherlands, Romania, and Poland.
Egg parasitoids collected from D. pini in Europe were
released in North Carolina in 1981 and 1982. These egg
parasitoids were provided by the Commonwealth Institute
of Biological Control, Delémont, Switzerland, but the
origin of the insects was not reported (Drooz et al., 1985).
Natural Enemies Found
Of the 37 species of par asitoids listed i n Table 1, the follow ing
seven species were accidentally or intentionally introduced
into North America: Monodontomerus dentipes (Dalman)
(Hymenoptera: Torymidae) (Fig. 8), E. amictorius, Pleolophus
basizonus (Gravenhorst) (Hymenoptera: Ichneumonidae), D.
fuscipennis (Fig. 9), Eupelmus spongipartus Foerster, Eupelmella
vesicularis (Retzius) (Hymenoptera: Eupelmidae), and Drino
bohemica Mesnil (Diptera: Tachinidae). The identication of
the latter species was questionable (Coppel et al., 1974).
Of the 32 million sawy cocoons mentioned above over
4 mil lion D. similis cocoons were collected in Poland in 1937.
Among the more than 15 species of parasitoids reared from
these cocoons were M. dentipes, E. amictorius and P. basizonus
Figure 7 Adult of the ichneumonid parasitoid Exenterus
amictorius. John H. Ghent, USDA Forest Service, Bug-
wood.org.
Figure 9 Adults of the eulophid parasitoid Dahlbominus
fuscipennis. John H. Ghent, USDA Forest Service,
Bugwood.org.
Figure 8 Adult of the torymid parasitoid Monodontomerus
dentipes. John H. Ghent, USDA Forest Service, Bug-
wood.org..
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(Finlayson and Finlayson, 1958). Monodontomerus dentipes was
reported as numerous, and E. amictorius and P. basizonus (as
Aptesis basizonia) were present in substantial numbers. All
three of these species, plus D. fuscipennis, were among the
parasitoid species reared from the other European sawy
species (Finlayson and Finlayson, 1958). The tachinid D.
bohemica was also reared from these collections, but there is
some confusion about the taxonomy of the species reared,
and the record of D. bohemica reported from D. similis may
be erroneous (Coppel et al., 1974). Over 30,000 specimens
of E. amictorius were reared (McLeod, 1972). The two exotic
parasitoids, M. dentipes and D. fuscipennis, which had been
previously introduced into North America, were reared
from host cocoons collected near Amery, Wisconsin,
for release in North Carolina (Drooz et al., 1985). The
parasitoids were mass reared using the procedures
developed by Fedde (1975).
Host Range Test Results
No host specicity tests were carried out and in this period
such work was not considered necessary.
Releases Made
Few releases of exotic parasitoids were made specically
against D. similis, but biological control of the species was
achieved by the release of oligophagous parasitoids against
related introduced sawy species (Coppel et al., 1974). Of the
exotic species of parasitoids that later were recovered from
D. similis in North America, the following were originally
released in eastern Canada (against G. hercyniae between 1933
and 1949): 288,036 P. basizonus, 882,360,000 D. fuscipennis,
and 30,960 E. amictorius (McGugan and Coppel, 1962).
Exenterus amictorius The rst releases of E.
amictorius were made against Gilpinia frutetorum ( Fabricius)
at Niagara in 1935 (McGugan and Coppel, 1962). Extenerus
amictorius was released in various localities from Nova
Scotia to Ontario and became one of the most successful of
the introduced species becoming established on Neodiprion
swainei Middleton in Quebec, N. sertifer in Ontario, and D.
similis in Wisconsin (McLeod, 1972).
Pleolophus basizonus In total, nearly a half million
individuals of P. basizonus, were released as biological
control agents against G. hercyniae, N. sertifer, and other
diprionid sawies in New Brunswick, Quebec, Ontario,
and Manitoba from 1933 to 1949. This parasitoid was
recovered near the release points in all provinces except
Manitoba from 1934 to 1958 (McGugan and Coppel, 1962).
Monodontomerus dentipes Some 2,397 M. dentipes
(reared from insects collected from populations of D. similis
in Oakville, Ontario) were released in Montreal, Quebec, in
1935 (Finlayson and Reeks, 1936). The establishment of M.
dentipes was conrmed in 1936, when an additional 12,000
parasitoids were also released (McGugan and Coppel, 1962).
Releases of 13,900 mated females of M. dentipes that were
mass reared for the biological control of D. similis in North
Carolina were made in 1979–1981 (Drooz et al., 1985).
Egg parasites Low numbers of three egg parasitoids,
Chrysonotomyia ruforum (Krausse), Chrysonotomyia ormosa
(Westwood) (both Hymenoptera: Eulophidae), and
Dipriocampe dipr ioni (Ferriere) (Hymenoptera: Tetraca mpidae),
were released along the Blue Ridge Parkway in North
Carolina in 1981 (Drooz et al., 1985). The parasitoids, which
had been reared from the European sawy Diprion pini, were
obtained from the Commonwealth Institute of Biological
Control, Delémont, Switzerland. A second release of 71 C.
ruforum and four C. ormosa was made in the Linville Falls area
of North Carolina the following year.
EVALUATION OF PROJECT OUTCOMES
Establishment of Agents and Eect on Pest
The only two exotic parasitoids in North America that
consistently occur in numbers high enough to inuence
the population suppression of D. similis are M. dentipes and
E. amictorius (e.g., in Wisconsin, see Coppel et al., 1974).
Neither of these species, nor D. fuscipennis, was introduced
into North America specically for control of D. similis;
rather, they established serendipitously in populations of
D. similis either by accidental introduction or intentional
introduction from releases against other sawy species.
The only purposeful biological control attempts against
D. similis were the translocation of established parasitoid
populations to areas where the parasitoids were absent
or in low density (i.e., augmentative biological control),
and a failed introduction of egg parasitoids into North
Carolina from Europe. Consequently, few attempts have
been made to quantify the impact of these parasitoids on
D. similis populations.
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Monodontomerus dentipes This parasitoid
probably arrived accidentally in North America with
its host D. similis because it was recovered soon after
the sawy was rst detected in North America in 1914
(Britton and Zappe, 1918). According to Finlayson
and Reeks (1936), M. dentipes was already established
in 1931 in Oakville, Ontario, Canada on D. similis. The
parasitoid is considered a key factor in the control of the
introduced pine sawy (Fedde, 1974). Surveys in North
Carolina populations of D. similis in 1978 failed to detect
any M. dentipes, which was the impetus for a mass rearing
project for that species. However, in 1979, before the
rst parasitoid releases were made, two individuals of
M. dentipes were reared from local populations showing
the species was already present in the area. After the rst
release, M. dentipes populations parasitized 45% of host
cocoons collected in 1980, but declined signicantly in
subsequent years (Drooz et al., 1985). The population
density of D. similis declined in 1982 in North Carolina,
which was attributed to the release of the parasitoid M.
dentipes, which had been introduced from insects reared
from collections in Wisconsin (USDA-FS, 1973–2005).
Exenterus amictorius This parasitoid was rst
collected in Wisconsin in 1961 from D. similis, having
probably spread from releases in Canada, and subsequently
replaced M. dentipes as the most abundant parasitoid of
D. similis (Mertins and Coppel, 1973). In Minnesota, E.
amictorius was the most abundant of the 16 parasitoids
encountered, with parasitism rates over 44% in both sawy
generations (Thompson et al., 1977)
Dahlbominus fuscipens This parasitoid established
following its release in North Carolina (Drooz et al., 1985),
from material collected in Wisconsin, but populations of
the parasitoid did not increase dramatically as did those of
M. dentipes.
Egg parasitoids None of the egg parasitoids released
in North Carolina in 1981–1982 became established, likely
because of the small numbers released, poor timing, and
logging in the release area (Drooz et al., 1985).
Nontarget Eects
No nontarget effects of the biological control of D. similis
have been reported.
Recovery of AectedTree Species or Ecosystems
Based on the review of occurrence records (USDA-FS,
1973-2005; NRCan, 1932–1995) for D. similis in North
America, outbreaks are usually of short duration with
limited tree mortality.
Broad Assessment of Factors Aecting Success or
Failure of Project
Many parasitoids were released into North America
for control of various exotic and native conifer-feeding
sawies. Only two of those species, M. dentipes and E.
amictorius, now seem to regulate populations of D. similis
(Coppel et al., 1974). McGugan and Coppel (1962) listed
M. dentipes as widely distributed in the range of D. similis
and “exerting a measurable degree of control.” It is worth
noting that M. dentipes arrived accidently into North
America with its host and became established before its
deliberate introduction, so the only new impact of the
biological control program was the establishment of E.
amictorius.
BIOLOGY AND ECOLOGY OF KEY
NATURAL ENEMIES
Three species of exotic hymenopterous parasitoids,
M. dentipes, E. amictorius, and D. fuscipennis, have become
established in D. similis populations in North America and
seem to regulate the sawy’s density.
Monodontomerus dentipes (Hymenoptera: Torymidae)
This species was one of the two most common parasitoids
of D. similis in Wisconsin (Mertins and Coppel, 1971) and
Minnesota (Weber, 1977) in the 1960s and early 1970s.
Monodontomerus dentipes usually attacks sawies in the
genera Diprion and Neodiprion. Other hosts reported in the
literature that are attacked less frequently include other
Hymenoptera, Diptera and Lepidoptera (Fedde, 1974).
Monodontomerus dentipes is a gregarious ectoparasitoid that
attacks and emerges from the host’s cocoon (Mertins and
Coppel, 1971). The female immobilizes the host within the
cocoon with her ovipositor and inserts a banana-shaped
egg into the host cocoon (Fedde, 1974). The female usually
deposits ve or six eggs within a cocoon, but up to 15 have
been observed. Within the cocoon, the parasitoid passes
124 inTroduCed pine saWfly X
The Use of ClassiCal BiologiCal ConTrol To Preserve foresTs in norTh ameriCa
through four larval instars, all of which feed externally
on the host. The parasitoid pupates within the cocoon
but does not form its own cocoon (Fedde, 1974). Adult
parasitoids emerge about 40 days after eggs are laid, but
some emerge much later, suggesting that they have entered
diapause (Fedde, 1975). The parasitoids mate immediately
after emergence (Fedde, 1975). The size of the adult of M.
dentipes depends on the size of the host and the number of
adults emerging from the cocoon (Fedde, 1974). The wasp
occasionally acts as a hyperparasitoid, and multiparasitism
or superparasitism can occur (Fedde, 1974).
Exenterus amictorius (Hymenoptera: Ichneumonidae)
This species is a primary parasitoid of larvae and it emerges
from the cocoon ( Mertins and Coppel, 1971). It lays its eggs
in the last instar before cocoon formation (Coppel et al.,
1974). According to McLeod (1972), based on observations
on N. swainei, the eggs of E. amictorius are usually laid
externally on the dorsum of the thoracic segments of the
host. The rst instar larva hatches after the host has spun
its cocoon and feeds externally on the host. The parasitoid
larva overwinters as a rst or second instar, and resumes
development in May. Pupation occurs in late May or early
June and the adults emerge about ve days later, rst males
and then females after about one week. This oliphagous
parasitoid is multivoltine and in its alternate generations
it attacks related diprionid species that are present as pre-
spinning eonymphs, including Neodiprion pratti banksianae
Rohwer, Neodiprion nanulus Schedl, and D. hercyniae in June
and July (McLeod, 1972). Adult E. amictorius emerge from
these hosts during August, before pre-spinning eonymphs
of its host N. swainei are available.
Dahlbominus fuscipennis (Hymenoptera: Eulophidae)
Dahlbominus fuscipennis is the third European species that
became established on D. similis in Wisconsin. Athough it
is regularly reared from the sawy, it is seldom numerous
(Mertins and Coppel, 1971). Dahlbominus fuscipennis is a
multivoltine pupal parasitoid of diprionid sawies. It is a
primary gregarious ectoparasitoid that attacks and emerges
from the host cocoon (Mertins and Coppel, 1971). The
parasitoid oviposits 10 to 50 eggs onto the surface of the
host. Eggs hatch in about two days and the neonate larvae
bore into the host (Rostás et al., 1998). The parasitoid
larvae complete the fth instar in 7 to 12 days, at which
time they pupate inside the host cadaver. Adults emerge
one to two weeks later (Rostás et al., 1998). The parasitoid
overwinters within the host cocoon as a larva, prepupa or
pupa (McGugan and Coppel 1962).
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Article
Full-text available
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Article
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Article
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Article
The oviposition behavior of Exenterus amictorius Panzer, an introduced parasite of pre-spinning eonymphs of the Swaine jack pine sawfly, Neodiprion swainei Middleton, was studied in a series of field experiments over a 5-year period in the Province of Quebec. The ability of this parasite to discriminate against hosts with previously deposited progeny varied significantly: discrimination was lacking at the beginning of the host’s spinning period, but was rapidly acquired and persisted to the end of the spinning period. The relationships were described by negative power functions of the form Iδ = aX−b, where Iδ = Morisita’s Index of Dispersion, and X = the number of days from the beginning of the host’s spinning period. The response of E. amictorius to changing host densities, however, was positive at all host densities and described by functions of the form Y = aXb, where Y = number of parasite progeny per host and X = number of hosts dropping into funnel traps at 2-day intervals during the spinning period. Over 67% of the variation in the number of progeny deposited by E. amictorius during a field experiment in 1969 was explained by changes in adult parasite density, and an additional 19% by changes in host numbers. This indicates strongly that the observed change in discrimination against previously deposited progeny bears no direct relationship to either host or parasite density. It was suggested that the change might be influenced either by a reduction in the parasite’s egg complement in time, or by an associative learning process.The density response of an indigenous parasite, Exenterus diprionis Rohwer, was comparatively much weaker and it seemed to lack the adaptive changes in discrimination against previously deposited progeny possessed by E. amictorius. Although attacks of the one species occurred independently of the other, in the event of multiparasitism E. amictorius always survived because of its faster rate of development in the host. The role of discrimination and of density response in the dominance of E. amictorius among the Exenterus spp. attacking N. swainei, and its successful establishment on a variety of North American diprionids, is discussed.