SEASONAL BIOLOGY OF METEORUS TRACHYNOTUS VIER. (HYMENOPTERA: BRACONIDAE) AND OF ITS OVERWINTERING HOST CHORZSTONEURA ROSACEANA (HARR.) (: )

J. MALTAIS,J. %GNIERE, C. CLOUTIER', C. HEBERT', and D.F. PERRY Forestry Canada, QuCbec Region, Laurentian Forestry Centre, PO Box 3800, Sainte-Foy, QuCbec, Canada GlV 4C7

Abstract Can. Ent. 121: 745-756 (1989) The braconid parasitoid Meteorus trachynotus Vier. was found in overwintered larvae of the obliquebanded leafroller, Choristoneura rosaceam (Harr.), on foliage of a vari- ety of deciduous species, well before the parasitoid's attack on the spruce budworm. ~horistoneurafun;iferana (Clem.). In the spring, percentage parasiiism of C. rosa- ceana by M. trachynotus was 8.0 and 18.8% in 1986 and8l987.res~ectivelv. Maximum parasitiHm on C. &miferana (35 and 4% in 1986 and 1987, r&p&tively)kas reached in late June, at a time when over 50% of M. trachynotus cocoons found on deciduous vegetation had emerged. Twenty days later, parasitoid's produced on C. fumiferana reached 50% adult emergence. The catches of adult parasitoids on sticky traps placed on deciduous trees and on conifers showed two periods of adult activity. Based on the sex ratio of captured parasitoids, male M. trachynotus \yere active at emergence sites, whereas females were found mostly in the habitats of available hosts. The phenology of C. rosaceana was observed in 1987. As indicated by light-trap captures, males fly sooner than females. Eggs were laid in July, and so the eqly larval stages were available to female M. trachynotus as overwintering hosts. Several parasitoids common to C. rosaceana and C. fumiferana were identified.

Le parasitoide braconide Meteorus trachynotus Vier. a CtC retrouvC, dans des larves hivernCes de la tordeuse bandes obliques, Choristoneura rosaceana (Harr.), sur le feuillage de diverses espkces feuillues, bien avant que ne commence I'attaque de la tordeuse des bourgeons de l'Cpinette, Choristoneura fumiferana (Clem.) par le para- sitoide. Au printemps, le pourcentage de parasitisme dis larves de C. rosaceana par M. trachynotus Ctait de 8,O et 18,8% en 1986 et 1987, respectivement. Les maxima de parasitisme sur C. fumiferana (35 et 4% en 1986 et 1987, respectivement) ont CtC atteints a la fin juin, pkriode B laquelle les cocons du parasitoide trouvCs sur les dCcidus Ctaient BmergCes ?I plus de 50%. Vingt jours plus tard, 1'Cmergence des adultes du parasitoide issus de C. fumiferana atteignait 50%. Les captures du parasitoi'de par des pihges collants disposes sur les feuillus et les coniferes ont montrC deux pkriodes d'ac- tivit6 des adultes. Le rapport des sexes dans ces captures a montre que les mfiles du parasitoide Ctaient actifs aux sites d'kmergence des cocons, alors que les femelles Ctaient retrouvCes principalement dans les habitats respectifs des tordeuses recherchkes comrne h6tes aux diffkrentes pCriodes. La phknologie de C. rosaceana a CtC suivie en 1987. La pCriode de vol des adultes de ce tortricide, dCtermin& B I'aide de pihges lumineux, montre une protandrie prononck. La pCriode de ponte des femelles a eu lieu pendant le mois de juillet, de sorte que les larves des premiers stades sont exposks aux femelles de M. trachynotus come h6tes d'hivernement. Plusieurs parasitoides communs i C. rosaceana et C. fumiferana ont Ctk identifies.

Introduction Meteorus trachynotus Vier. is a parasitoid of fifth- and sixth-instar larvae of the spruce budworm. This parasitoid often increases in relative abundance in the final years of bud- worm outbreaks (Dowden and Carolin 1950; Blais 1960; Miller 1963; Miller and Renault 1976; unpublished data). The biology and seasonal history of M. trachynotus are not well known. It has been suggested the M. trachynotus overwinters as an egg or larva in a host

'Department of Biology, Lava1 University, Sainte-Foy, Qukbec, Canada GlK 7q4. 746 THE CANADIAN ~MO~DGIST September 1989 other than the spruce budworm (Daviault 1949; Blais 1960; Dowden and Carolin 1950). Changes in abundance of available alternate hosts may explain the large fluctuations of parasitism by this parasitoid on spruce budworm (McGugan and Blais 1959). Of the known hosts of M. trachynotus (Krombein et al. 1979; Pogue 1985), only the obliquebanded leafroller, Choristoneura rosaceana (Harr.),has a life cycle making it a likely overwin- tering host in eastern Canada. Larvae of C. rosaceana feed at least until the second larval instar before entering diapause in the fall (Gangavalli and AliNiazee 1985). The seasonal history of this tortricid is variable (Madsen et al. 1984; AliNiazee 1986), and it is little known in QuCbec. The objectives of this study were to identify major overwintering hosts of M. tra- chynotus, and to document the seasonal history of the parasitoid and its overwintering hosts. Materials and Methods The study began in 1986 near Armagh, QuC. (46"46'N, 70"39'W, altitude: 270 m), within and around a study area described by Lethiecq and RCgnikre (1988). In 1987, the study was continued near Lake Solitaire, in St-Maurice Provincial Park, QuC. (47"01rN, 73"12'W, altitude: 335 m). Seasonal Biology of M. trachynotus. Foliage sampling. The search for overwintering hosts of M. trachynotus was carried out in spring (May, early June) and late summer (July, August) of 1986, before and after the time during which M. trachynotus attacks and devel- ops in the spruce budworm (McGugan 1955). Lepidopterous larvae and pupae, as well as parasitoid cocoons resembling those of M. trachynotus were collected from various habitats, from ground litter and from foliage of various species of deciduous trees and shrubs. Foliage samples in large trees were collected with pole pruners and examined in the field. Visual examination and beating over collecting mats were used to survey the foliage of lower vegetation. Caterpillars were reared at 20°C under natural photoperiod in glass jars (250 mL). They were fed frequently changed foliage of the original tree species. They were kept until they died or a parasitoid or emerged. When possible, the were identified from larvae and pupae, and emerged were used to confirm these identifications. In 1987, sampling from decid- uous species was conducted throughout the summer, but was concentrated on hosts of C. rosaceana. All parasitoids emerging from these rearings were identified. Spruce budworm larvae were removed from foliage samples of balsam fir (Abies balsamea [L.] Mill.) and white spruce (Picea glauca [Moench.] Voss) which were col- lected, using pole pruners, from mid-crown at intervals of 2-3 days. These larvae were reared on artificial diet (McMorran 1965) using the method of Thomas (1984). The devel- opment stage of the insects, parasitism by M. trachynotus, and cocoons of the parasitoid found on foliage were recorded. density was expressed per kilogram of foliage (RCgnibre et al. 1989). Adult trapping. Adult M. trachynotus were sampled using a network of yellow sticky traps (Seabright Enterprises, Emeryville, CA), checked every 2-3 days from May to mid- September. In 1986, 100 traps were placed in five habitats, dominated by Acer saccharum (Marsh), Populus tremuloides (Michx.), (Marsh), Pinus strobus (L.), and Pinus resinosa (Ait). In each habitat, 10 traps were located at mid-crown (average 8 m above ground), and 10 at 30 cm above ground. Seventy traps also were placed on trees and shrubs of Rubus idaeus (L.), P. tremuloides, B. papyrifera, and Prunus pensylvanica (L.F.). A network of 70 traps also was operated within the spruce budworm sampling area. These traps were placed in the mid-crown of balsam fir and white spruce trees (average 6 m above ground). In mid-June, 35 additional traps were placed near P. pensylvanica, volume 121 THE CANADIAN ENTOMOLOGIST 747 Prunus virginiana (L.), Corylus cornuta (Marsh), R. idaeus, and Alnus rugosa (du Roi- Spreng), hosts of the obliquebanded leafroller (Chapman et al. 1968). In 1987, 120 traps were placed, at an average height of 1.5 m, on shrubs of five species: C. cornuta, (Lam.), R. idaeus, P. pensylvanica, and A. rugosa. Another network of 120 traps was placed on balsam fir and white spruce trees at an average height of 7 m. Seasonal Biology of C. rosaceana. Development of immature stages. The development of C. rosaceana was monitored from early May to mid-July 1987. Larvae and pupae were collected in the vicinity of Lake Solitaire on A. spicatum, B. papyrifera, C. cornuta, A. rugosa, P. pensylvanica, P. tremuloides, and R. idaeus. Larvae were reared in glass jars as described above. Larval instars were determined by head capsule width, based on a frequency distribution of head capsule widths compiled from 177 C. rosaceana larvae reared on R. idaeus. Information on instars 3-7 was obtained from larvae that overwintered in the third instar. Progeny of these insects were reared at 20°C, 12L: 12D photoperiod to induce diapause (Gangavalli and AliNiazee 1985), to provide head capsule widths for instars 1 and 2. Larval density of C. rosaceana was measured on R. idaeus, A. spicatum, C. cornuta, and B. papyrifera. During larval development, C. rosaceana were counted on 500 45-cm branches of each species. Adult flight period. Pheromone traps were used to observe the flight period of male C. rosaceana. Fifteen to 20 Biolure traps, containing a synthetic pheromone (Concep Membranes, Bend, OR) (Roelofs and Hill 1979), were placed on different host plants of C. rosaceana from mid-June to mid-September in 1986 and 1987. Captures were recorded weekly. Traps were changed in mid-August. Four light traps (Universal light trap, model 2851K, BioQuip products, Santa Monica, CA) were operated in 1987 from mid-June to late July. Moths captured were identified to species, sexed, and counted daily. To estimate the percentage of oviposition prior to capture, and thus the approximate time that eggs were present in the field, a method similar to that developed by Thomas et al. (1980) for spruce budworm was used. The wing surface-area and dry weight of captured females were measured, and a linear relationship between the two variables was estimated. The slope of the dry weight - wing surface-area relationship for wild moths (m,) was then compared with those established for fully gravid (m,) and spent (m,) females reared in the laboratory from field-collected larvae. The proportion of eggs laid (p,),before capture by a group of females is given by:

mg- m, = [ m-m 1 Egg introduction. Because eggs and early-larval stages of C. rosaceana were dif- ficult to find in the study plots, egg masses were introduced in four small cages (1 m on all sides) covering shrubs of C. cornuta and A. spicatum. These eggs had been laid on waxed paper by females that had emerged from field-collected larvae and pupae and been reared with one or two males in 250-mL glass jars. One hundred and five egg masses containing an average of 200 eggs each, laid between 10 and 20 July, were attached to the underside of leaves inside the cages. Cheese cloth was wrapped loosely around stems of the shrubs to provide larvae of C. rosaceana with an abundance of hibernation sites. Development was observed every 2-3 days. Eight female M. trachynotus reared from field-collected spruce budworm were intro- duced in each cage. Part of the diapausing C. rosaceatm larvae were collected in mid- September and dissected to determine the presence of M. trachynotus and its overwintering stage. The remainder were recovered in early spring, and reared on R. idaeus until par- asitoid emergence. 748 THE CANADIAN ENTOMO~IST September 1989 Results and Discussion Seasonal Biology of M. trachynotus. Foliage sampling. A total of 2002 lepidopterous larvae belonging to 73 species were reared during the spring collection period (May to early June). During the late summer collections (July and August), 1140 larvae of 103 species were reared. Only 34 species were represented by more than 10 individuals (Table 1). Thirty-one specimens of M. trachynotus were recovered from these rearings, all but one of which emerged from C. rosaceana larvae collected in the spring. One specimen perhaps emerged from Sparganothis acerivorana (Mack), but we consider that this is a likely misidentification, because of the difficulty in distinguishing these two tortricids in the larval stages. Also, the life cycle of this species in eastern Canada is similar to that of the spruce budworm in that larvae enter diapause soon after eggs hatch (Martineau 1985) and are unavailable as overwintering hosts for M. trachynotus. Parasitism of C. rosaceana larvae by M. trachynotus was highest in late May, well before any adults were caught on sticky traps, and decreased in early June as a result of emergence from the host (Figs. lA, 2A). Meteorus trachynotus cocoons, 50% of which had emerged, were found on deciduous vegetation near moribund C. rosaceana larvae on 17 June 1986 (Fig. 1A). In 1987, the density of M. trachynotus cocoons emerged from C. rosaceana peaked on 8 June and adults emerged between 12 and 23 June (Fig. 2A). Meteorus trachynotus was first found parasitizing spruce budworm larvae at the same time as adult parasitoids were emerging from cocoons on deciduous foliage. Parasitism peaked at the end of June in both years. Cocoons of the second generation first appeared on conifer foliage in late June (Figs. lB, 2B), and adults of that generation emerged 2-3 weeks later (observed in 1986, Fig. 1B). The period of parasitism on spruce budworm corresponded to the presence of the host's sixth instar (Figs. lC, 2C). Moribund individuals from which M. trachynotus had emerged (McGugan 1955) constituted about 80% of spruce budworm population at the end of the 1986 season (Fig. 1C). In 1987, the frequency of M. trachynotus on the spruce budworm was much lower, and few moribund larvae were found. Captures of adult M. trachynotus on traps. Although the number of M. trachynotus adults caught on sticky traps in any given year and habitat was rather low during May and June, these data confirmed the occurrence of two adult generations (Figs. 1,2) . The first adults caught in conifers were mostly females and were trapped at the time of emergence of adults from cocoons on deciduous vegetation. Captures in deciduous trees were very low during this period, and were almost exclusively males. Similarly, adults of the gen- eration produced on spruce budworm and trapped on conifers were mostly males. On deciduous trees, the peak of capture of second-generation adults was shifted by several days, and consisted mostly of females. Seasonal Biology of C. rosaceana. Development of the immature stages. Larval head capsule width in the genus Choristoneura is a good indicator of instar, although sexual dimorphism and supernumerary instars may cause confusion (Schmidt and Lauer 1977). On the basis of successive molts, most larvae reared on R. idaeus had seven instars. Head capsule measurements overlapped somewhat, particularly between second and third instars (Fig. 3). There does not seem to be much growth during these two instars in the overwin- tering generation. Instar determinations of field-collected larvae are approximate, because it is likely that head capsule size and the numbers of larval instars are affected by food quality. Choristoneura rosaceana larvae found on foliage in early May were 20% third and 80% fourth instar (Fig. 4). These results differ from those of AliNiazee (1986) who found that fewer than 20% of overwintering larvae were in the fourth instar. This proportion is affected by temperature (Gangavalli and AliNiazee 1985); some molting may have occurred volume 121 THE CANADIAN ENTOMOLDGIST 749 Table 1. List of lepidopteran species collected in May and early June (Early) and in July and August (Late) in Armagh (1986) and Lake Solitaire (1987), Quk.

Number collected Species Early Late Tortricidae Epinotia solandriana (L.) 377 0 Sparganothis acerivorana (Mack.) 142 0 Choristoneura rosaceana (Harr.) 839 0 Pseudosciaphila duplex (Wlsm.) 190 0 Pseudexentera oregonana (Wlsm.) 36 0 Epinotia cruciana (L.) 21 0 Choristoneura conj7ictana (Wlk.) 15 0 braunana (McD.) 0 70 Acleris chalybeana (Fern.) 0 16 Acleris logiana (Cl.) 0 62 Acleris semiannula (Rob.) 0 31 Archips argyrospila (Wlk.) 11 0 Geometridae Protoboarmia porcelaria indicataria (Wk.) 16 0 Hypagyrtis piniata (Pack.) 13 0 Lambdina jiscellaria jiscellaria (Gn.) 0 24 Melanolopha canadaria (Gn.) 0 18 Eupithecia sp. 0 17 Biston betularia cognataria (Gn.) 0 16 Probole arnicaria (H.-S .) 0 15 Lobophora nivigerata Wlk. 0 13 Eutrapela clemataria (J.E. Smith) 0 10 Noctuidae Ipimorpha pleonectusa Grt. 28 0 Anomogyna elimata (Gn.) 15 0 Syngrapha alias (Ottol.) 10 0 Bomolocha sp. 0 16 Oecophoridae Nites grotella (Rob.) 78 0 Nites atrocapitella (Rob.) 21 0 Gelechiidae Anacampsis niveopulvella (Cham.) 21 0 Chionodes obscurusella (Cham.) 12 0 Other families Caloptilia invariabilis (Braun) 0 20 1 Lophocampa maculata Harr. 0 24 Charidryas harrisii harrisii (Scudd.) 0 30 Pseudothyatira cymatophoroides (Gn.) 0 26 Orgyia L. leucostigma (J.E. Smith) 0 24 prior to the onset of sampling in 1987, because of an unusually warm spring. Pupation of C. rosaceana occurred from mid-June to early July (Fig. 4). Twelve parasitoid species other than M. trachynotus were reared from C. rosaceana. Several of the common species were also parasitoids of the spruce budworm: Itoplectis conquisitor (Say). Phaeogenes maculicornis (Cres.), Ephialtes ontario (Cres.), and Glypta jkmiferana (Vier.). The only other common species was Macrocentrus iridescens (Fr.). The density of C. rosaceana, expressed as number of lame per 100 leaves, was rather low at Lake Solitaire in 1987: 0.034 (6117580) on A. spicatum, 0.027 (9132830) on C. cornuta, and 0.013 (5121955) on B. papyrifera. It was significantly higher, 0.16 (1318105), on R. idaeus (x2= 31.65, df= 3, p<0.001). 750 THE CANADIANENTOMOLOGIST September 1989

fOSUC8UnU A X PARASITISM 7 z 0 a LIVE COCOONS 5 SE IEMPTY COCOONS I r6 Z0 0 l"'~1"''l~'''0

6th c. fum/fufmu

PUPAE "","",

150 175 200 225 250 I June I July I August 1 DAY OF YEAR FIG. 1. Seasonal biology of M. trachynotus, Armagh, Quk., 1986. (A) Parasitism on C. rosaceana (n=2243) and number of cocoons found on deciduous trees; (B) parasitism on C. jiuniferana and density of cocoons per lulogram of conifer foliage (n= 6-355); (C) development of C. fumiferana (n = 6-355); (D)capture of M. tra- chynozus adults on sticky traps on conifers and (E) on deciduous vegetation.

Adult flight period. No male C. rosaceana moths were caught in pheromone traps at the end of the 1986 season (Fig. 5A). Three males were caught in September 1987. Thus, a small proportion of the population did not enter diapause in August and continued development at least until moth emergence. Diapause in this species is facultative (Chap- man et al. 1968; Gangavalli and AliNiazee 1985), and the number of generations per year can vary between host plant and locality (Chapman and Lienk 1971). Weather may influ- ence the size of the second generation (AliNiazee 1986). Thus unusually warm early spring temperatures may have resulted in a small second generation of C. rosaceana in 1987. The first male flight period peaked 20 days earlier in 1987 than in 1986. Males were caught earlier than females in light traps (Fig. 5B). Protandry was reported for the obliquebanded leafroller by Onstad et al. (1985). Traps caught more males than females. It is not unusual for adult males of Choristoneura species to be more active fliers than females (Greenbank 1957). Relationships between wing surface area (x) and dry weight Cy) of females were linear, and were estimated by regression analysis using dummy variables to test the significance volume 121 THE CANADIAN ENTOMOLOGIST 75 1 2 4 c. rosoceono v, A X PARASITISM 0Z % 12 LIVE COCOONS IEMPTY COCOONS 0z U 0 0

100 c 6th C. fumlferunu - PUPAE % 50 -

0 '..I'..."'.

150 175 200 225 May I June 1 July I August I DAY OF YEAR FIG. 2. Seasonal biology of M. trachynotus in Lake Solitaire, QuB., 1987. (A) Parasitism on C. rosaceana (n= 38-76) and number of cocoons found on deciduous trees; (B) parasitism on C. fumiferana and density of cocoons per kilogram of conifer foliage (n= 13-107); (C) development of C. fumiferana (n= 13-107); (D) capture of M. trachynotus adults on sticky traps on conifers and (E) on deciduous vegetation. of parameter-value differences (Gujarati 1970). The lines (common R2 = 0.82) were forced through a common intercept (- 5.56 + 2.41 mg). Slopes were significantly different (t= 17.59, df = 68, p<0.001) between spent (0.175 + 0.040 mg/mm2) and gravid females (0.429 + 0.044 mg/mm2). This relationship did not vary significantly with capture date for females caught in light traps (Fig. 6). From the 0.209 2 0.026 mg/mm2 slope, we estimated (using Eq. [I]) that these females had laid 87% of their eggs before capture. Chapman and Lienk (1971) reported that there was a 1-day preoviposition period and that females laid 75% of their eggs during the following 3 days. Thus, females caught in our light traps were at least 4 days old. Egg introduction. Eggs obtained from females reared in the laboratory were placed in field cages between 10 and 20 July 1987, at the time when wild females were ovipositing (as indicated above). The vast majority of larvae from these eggs developed to the second instar and entered diapause before mid-August (Fig. 4). Of the eight larvae still feeding at the end of August, three were in the second and five in the third instar. No active larvae were found after that date. As determined by dissection of hibernacula, 90% of the larvae overwintering inside the cages entered diapause in the second instar, the rest in the third (n = 61). 752 THE CANADIANE~OLDGIST September 1989

HEAD CAPSULE WIDTH (mm) FIG.3. Frequency distribution of head capsule widths of C. rosaceana larvae reared on R. idaeus. Vertical lines represent limits used to separate instars.

As determined by dissection of diapausing C. rosaceana larvae, parasitism by M. trachynotus inside the cages was 49% (28157). From morphological descriptions of the larval stages of M. trachynotus (J.C. Thireau, Forestry Canada, Laurentian Forestry Centre, Sainte-Foy, QuCbec, pers. comrn.), all 28 individuals were in the first instar. Meteorus trachynotus emerged from the fifth instar of C. rosaceana larvae removed from the cages and reared in early spring (1 1/31). These results confirm the ability of this parasitoid to overwinter in diapausing larvae of C. rosaceana.

- WILD --INTRODUCED -+ 2nd n I I 1% 11 ,' ', 3rd I+, I1 I I 4 f '\I

I b, II I '5 I I I,,' 11 I I 1'1 )I1 I I 'I 1 11 I 1 v f I I I .- / -,0 Irr''17'''1 125 150 175 200 225 250 May I June I July I August I DAY OF YEAR

FIG.4. Development of C. rosaceana (n = 4-149), Lake Solitaire, Que., 1987. Volume 121 THE CANADIAN ENTOMOLOGIST 753

175 200 225 250 275 June 1 July ( August 1 September 1 DAY OF YEAR FIG. 5. (A) Capture of C. rosaceana in pheromone traps in Armagh, QuC. (1986) and in Lake Solitaire, QuB. (1987); (B) capture of C. rosaceana in light traps, in Lake Solitaire (1987).

Conclusion Our results confirm that M. trachynotus is a bivoltine parasitoid requiring two host species to complete its yearly life cycle. Several Lepidoptera are known to be summer hosts of this parasitoid (Krombein et al. 1979; Pogue 1985) although the spruce budworm, when present, is the most prevalent. In our study, C. rosaceana was the only unequivocal overwintering host. Unlike many other species of Choristoneura, diapause in this tortricid is facultative and induced by short day length and cool temperatures occurring during the first and second instars (Gangavalli and AliNiazee 1985). Thus, larvae feed until the end of the second or third instars at a time when M. trachynotus females are searching for hosts. Other Lepidoptera feeding as larvae in late summer were not found to harbor the parasitoid. It is likely that this parasitoid does not attack larvae once they have spun a hibernaculum. For adult M. trachynotus, finding overwintering hosts implies movement from con- iferous hosts of spruce budworm to deciduous hosts of C. rosaceanu. It seems likely that, although males of this parasitoid species stay in the vicinity of their emergence site in search of mates, females move, after mating, in search of hosts. This would explain the male-biased sex ratios observed in adult emergence habitats, and female-biased ratios in the habitats of available hosts. The delayed peak of female M. trachynotus activity in deciduous vegetation may have resulted from changing availability of host larvae. It is not clear whether females search for late-developing spruce budworm larvae before moving to deciduous vegetation. The numerical importance of parasitism by M. trachynotus on summer hosts other than spruce budworm is not known, but this may also determine the timing of peak parasitoid activity. - THE CANADIAN EKIU3MOLOGIST September

A 1 to 8 July 0 9 to 14 July 19 to 24 July

A

WING SURFACE AREA (mrn2)

FIG.6. Relationships between dry weight and wing surface area for female C. rosaceana, Lake Solitaire, QuC., 1987. Line (A), fully gravid females; line (B), spent females.

The possibility that some individuals of M. trachynotus overwinter as adults cannot be totally dismissed. However, there does not seem to be any reproductive diapause, which is the norm in short-lived insects that overwinter as adults (Danks 1987). Furthermore, parasitism of spruce budworm does not begin until well into the summer although the parasitoid can attack small larvae (unpublished data). Finally, no adult M. trachynotus was caught prior to the emergence of cocoons issued from C. rosaceana larvae. Choristoneura rosaceana is a polyphagous insect (Chapman et al. 1968) that feeds on plants commonly encountered in forest environments prone to spruce budworm attack. Its numbers do not seem to get as high as those of the spruce budworm, although it is both an agricultural and a forest pest (Madsen and Madsen 1980; Madsen et al. 1984; Chapman and Lienk 1971). This may explain why parasitism by M. trachynotus on spruce budworm is low during outbreaks, but increases when the populations of spruce budworm decrease (Dowden and Carolin 1950; Blais 1960; Miller 1963; Miller and Renault 1976). During the decline of a spruce budworm outbreak, parasitism by M. trachynotus may lead to a reduction in populations of C. rosaceana, which would limit the capacity of this parasitoid to remain an important natural enemy of spruce budworm. Nevertheless, when spruce budworm are scarce, several other species of Lepidoptera are available as summer hosts for the parasitoid. The unpredictable nature of parasitism by this species on spruce bud- worm may be due in part to the dynamics of both host populations, but it may also be influenced by the adequacy of the synchrony in the development of all three insects. Management practices aimed at enhancing the stability and prevalence of C. rosa- ceana populations in forests prone to spruce budworm attack would facilitate the activity of this parasitoid which seems to play an important role in hastening the decline of spruce budworm outbreaks. Acknowledgments We thank Thkrgse Arcand for rearing and identifying insects collected in 1986. B.E Cooper, H.J. Teskey, M. Sharkey, J.R. Barron, and H.E. Bisdee of the Biosystematics Volume 121 THE CANADIAN ENTOMOLOGIST 755 Research Centre (Ottawa, Ont.) identified the parasitoids. Thanks to Vincent Nealis and to an unidentified reviewer for their helpful comments on an earlier draft. Assistance was also provided by the QuCbec Department of Energy and Resources. References AliNiazee, M.T. 1986. Seasonal history, adult activity and damage of the obliquebanded leafroller, Choriszo- neura rosaceana (Lepidoptera: Tortricidae), in filbert orchards. Can. Ent. 118: 353-361. Blais, J.R. 1960. Spruce budworm parasite investigations in the lower St-Laurence and Gasp6 regions of . Can. Ent. 92: 384396. Chapman, P.J., and S.E. Lienk. 1971. Tortricid fauna of apple in New-York; including an account of apple occurrence in the state, especially as a naturalized plant. N.Y. State Agric. Exp. Stn. (Geneva, N.Y.) Spec. Publ. Chapman, P.J., S.E. Lienk, and R.W. Dean. 1968. Bionomics of Choristoneura rosaceana. Ann. ent. Soc. Am. 61: 285-290. Danks, H.V. 1987. Insect Dormancy: An Ecological Perspective. Biological Survey of Canada Monogr. 1. Ottawa. 439 pp. Daviault, L. 1949. Les parasites de la tordeuse des bourgeons de I'tpinette (Choristoneurafumiferana Clem.) dans la province de Qutbec. Rapp. Soc. Qutbec Prot. Plantes, 1948-1949. pp. 1-7. Dowden, P.B., and V.M. Carolin. 1950. Natural control factors affecting the spruce budworm in the Adirondacks during 19461948. J. econ. Ent. 43: 774783. Gangavalli, R.R., and M.T. AliNiazee. 1985. 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