Hemlock Looper Research Articles

Linking adaptation, delimitation of evolutionarily significant units (ESUs), and gene function: a case study using hemlock looper ecotypes

Developing genetic markers for the identification of recently diverged groups, such as ecotypes or species complexes, remains difficult due to challenges with incomplete lineage sorting, hybridization and introgression. Genome‐wide scans of single nucleotide polymorphisms (SNPs) have proven useful for inferring patterns of genetic differentiation at the population level. In combination with a new analytical technique, the discriminant analysis of principal components (DAPC), and within the framework of iterative taxonomy, it may also be possible to extract a combination of SNPs as markers for the delimitation of closely related groups. In addition, since DAPC identifies the loci contributing the most to group clustering, it may be possible to link putative biological function to differences that define group boundaries. We tested this technique on two ecotypes of the hemlock looper (Lambdina fiscellaria), which differ in terms of number of larval stadia, developmental rate and fecundity. It was possible to separately cluster the two ecotypes with 95% correct assignment using 27 SNPs. We also determined that a storage hexamerin carried eight of these SNPs, including the two highest contributing loci, of which the top contributor was nonsynonymous. Other studies have found this protein to be highly expressed just before metamorphosis, pointing to a possible connection between its role in clustering ecotypes and its biological function. These SNP markers can now be further developed for high throughput delimitation of individuals of unknown ecotype identity.

Seasonal Ecology and Thermal Constraints of <I>Telenomus</I> spp. (Hymenoptera: Scelionidae), Egg Parasitoids of the Hemlock Looper (Lepidoptera: Geometridae)

We describe seasonal patterns of parasitism by Telenomus coloradensis Crawford, Telenomus droozi Muesebeck, Telenomus flavotibiae Pelletier (Hymenoptera: Scelionidae), and Trichogramma spp. (Hymenoptera: Trichogrammatidae), egg parasitoids of the hemlock looper, Lambdina fiscellaria (Guenée) (Lepidoptera: Geometridae), after a 3-yr survey of defoliated stands in the lower St. Lawrence region (Quebec, Canada). Results from sentinel trap sampling indicate that T. coloradensis and T. droozi are the most common species, whereas parasitism by T. flavotibiae and Trichogramma spp. is rare. Telenomus coloradensis and T. droozi show similar seasonal periods of parasitism, both species being active in early spring (late April) at temperatures as low as 4°C. Using thermal threshold (T(0)) and thermal constant (K) for immature development of T. coloradensis males and females from egg to adult emergence, we estimated that the spring progeny emerges in the middle of the summer while hemlock looper eggs are absent from the forest environment. Parasitoid females would then mate and remain in the environment to 1) exploit alternate host species, 2) enter into quiescence and later parasitize eggs laid by hemlock looper females in the fall, 3) enter into a reproductive diapause and parasitize hemlock looper eggs only the next spring, or all of these. Although previous studies have shown that T. coloradensis can overwinter in its immature form within the host egg, our field and laboratory results indicate that in the lower St. Lawrence region, this species principally enters diapause as fertilized females, with a mean supercooling point of -30.6°C in the fall.

Impact of increasing temperatures and exposure duration on egg hatch in the hemlock looper, Lambdina fiscellaria

As the growing season is expected to begin earlier under climate change, insects should initiate reproduction several days or weeks earlier than they used to. In eastern Canada, hemlock looper (HL) Lambdina fiscellaria (Guenée) (Lepidoptera: Geometridae) females generally oviposit in September, with eggs entering an obligatory diapause quickly after their deposition. We therefore simulated an early start of the HL reproduction cycle of 2, 4, 6, or 8 weeks to examine the extent to which freshly laid eggs from two populations (island and mainland) can withstand exposure to four temperature conditions (15, 20, 25 °C, or fluctuating temperature in an outdoor insectary), with all treatments ending on 1 September 2007. On this date, half the eggs from each population were immediately incubated at 15 °C, while the rest were stored in an outdoor insectary until their incubation at 15 °C the following spring. In a separate experiment, the effect of temperature on pre-diapause duration was determined from the number of days required for eggs to change colour after oviposition. The pre-diapause phase was completed faster as temperature increased. Regardless of incubation date and population, percent hatch decreased significantly after 6-8 weeks of exposure to 25 °C or in the outdoor insectary. Under most treatments, the odds of dying as pharate larvae increased with exposure duration. When eggs were incubated at 15 °C immediately after treatment, time to hatch and diapause duration remained constant over treatments, except at 25 °C when they both decreased. After 8 weeks of exposure to 15 or 20 °C, eggs transferred outdoors were more likely to hatch precociously than those exposed to 25 °C or insectary conditions. Globally, mortality seemed greater among eggs stored outdoors than among those kept indoors. Most eggs that survived the winter hatched synchronously after incubation in spring. Overall, larger eggs from the island population survived better than smaller eggs from the mainland population.

Linking aerial survey data of forest insect defoliation and tree ring data to estimate forest level growth losses

Aerial surveys provide valuable information on the scale and severity of defoliation and mortality caused by forest insects. However, methods to estimate the losses in growth using aerial survey data are not available. This study presents a method to link aerial survey data of location and severity of insect defoliation to tree ring series of radial growth in order to quantify potential growth losses due to defoliation. The method includes estimation of potentially confounding effects of climate. As an example we used aerial surveys of hemlock looper defoliation in the Mt. Revelstoke region of British Columbia, and tree ring series of radial growth of 351 western hemlock trees located in 22 plots and exposed to various levels of periodic defoliation. An autoregressive conditional heteroskedasticity time-series model (ARCH) of standardized growth indices identified significant direct and lagged effects of climate and defoliation on radial growth between 1930 and 2005. Defoliation effects were statistically significant in all plots (P<0.05). The variation in both timing and strength of estimated growth reductions varied considerably among plots. During years of observed defoliation the radial growth was reduced by an average of 10%. Growth reductions attributed to defoliation were most pronounced in the second and third year of a looper outbreak. Our modelling approach linked tree ring data to aerial survey data of defoliation through a logistic distance dependent threshold function and affords a quantitative estimation of regional growth losses.

Evidence that soil depth and clay content control the post-disturbance regeneration of balsam fir and paper birch under heavy browsing from deer

It is not well understood why successful regeneration of balsam fir and paper birch was observed in the south-central portion of Anticosti Island, despite a high-density deer population reputed to severely browse the seedlings of these 2 species. The area where this regeneration occurred was severely affected by a hemlock looper epidemic in the early 1970s and was specifically confined to one geologic formation (Chicotte). We tested whether or not the occurrence of balsam fir and paper birch coincided with a certain range of soil properties (pH, exchangeable cations, soil depth, clay content, and forest floor thickness). Out of 49 plots surveyed, balsam fir and paper birch respectively occurred on 30 and 25 plots, while black or white spruce occurred on all plots. There was co-occurrence of balsam fir and paper birch in 15 plots in which the relative abundance of paper birch was low. Multivariate regression trees (MRT) indicated that balsam fir occurred on shallow soils, whereas paper birch occurred on deep soils. On shallow soils, MRT indicated better regeneration of balsam fir in soils with low clay content. Results suggest 2 concurrent mechanisms related to site fertility leading to the regeneration of balsam fir and paper birch. The first involves low fertility conditions that stimulate balsam fir to produce higher concentrations of anti-herbivore compounds. The second mechanism involves increased tolerance of birch saplings to repeated deer browsing on the deeper and more fertile soils. Future research should strive to confirm these mechanisms and understand why they were efficient on the Chicotte formation but not elsewhere on the island.

Modeling insecticide protection versus forest management approaches to reducing balsam fir sawfly and hemlock looper damage

A decision support system (DSS) for improved management decision making and to reduce impacts of forest insect outbreaks was developed and implemented for two defoliators, hemlock looper ( Lambdina fiscellaria fiscellaria Guen.) and balsam fir sawfly ( Neodiprion abietis Harris), in District 15, a 336,805 ha forest managed by Corner Brook Pulp and Paper Ltd. in western Newfoundland, Canada. Over the past 15 years, 56% and 12% of the landbase were defoliated by balsam fir sawfly and hemlock looper, which had major effects on forest growth and yield. Relationships between reduced growth and survival and cumulative defoliation were quantified for each insect, to permit calculation of relative impact per forest stand as a function of defoliation, stand age, and species composition. These were integrated into a forest estate model to project effects on timber supply for 25 years. Defoliation during 1996–2008 was estimated to reduce total operable softwood growing stock and softwood harvest level by 26% and 31%, respectively, for balsam fir sawfly, and by 2–3% for the smaller-scale hemlock looper outbreaks. Given the long-term influence on forest structure, effects of defoliation on yield were projected to continue for up to 60 years after defoliation ceased. Sensitivity analysis using different defoliation scenarios suggested that maximum reductions in harvest levels could be reduced from 40% to 17% by protecting the most susceptible 25% of the landbase using biological insecticides, and minimized further to 9% by re-optimization of harvest schedules to reduce losses. This DSS provides a tool to help forest managers decide when and where to use biological insecticides, and how to use rescheduling of harvest, forest restructuring or planned salvage to reduce future losses.

Effect of temperature and host tree on cold hardiness of hemlock looper eggs along a latitudinal gradient

The hemlock looper, Lambdina fiscellaria, is an economically important insect pest of Canadian forests which overwinters as eggs. Although the hemlock looper causes extensive damages, no information on the mechanisms related to its cold tolerance is known. The objective of this study was to determine the effect of temperature and exposure duration on hemlock looper winter survival but also to identify seasonal supercooling capacity and cryoprotectant levels of three populations along a latitudinal gradient. As host plant may contribute to offspring overwintering success, cold tolerance of hemlock looper eggs from parents whose larvae were fed on three different tree species was also measured. Mean supercooling point (SCP) of hemlock looper eggs was lower than −30°C from October through the following spring with values being as low as −47°C in February. Trehalose was the most abundant sugar found in hemlock looper eggs with a peak concentration of 0.3μgmg−1DW−1. Glycerol, a polyol, was more often absent in eggs of the different populations and tree species tested in the study. When exposed to different temperature regimes for various periods of time, significant mortality of hemlock looper eggs occurred at higher temperatures than the mean SCP. Thus, hemlock looper could be considered as a chill tolerant species. No clear pattern of population and host plant effects on SCP and cryoprotectants was detected in this study. However, when exposed to different winter temperatures and exposure duration, hemlock looper from higher latitudes survived better (survival rates ranging between 0 and 89% at −20°C) than those from lower latitudes (survival rates ranging between 0 and 56% at −20°C). Our results may contribute to a better understanding of hemlock looper winter biology and thus facilitate predictions of outbreaks and range expansion.

Insights into herbivore distribution and abundance: oviposition preferences of western hemlock and phantom hemlock loopers

AbstractKnowledge of the factors affecting host selection by herbivorous insects is essential to predictions of their distribution and abundance over landscapes. In the laboratory, we studied the oviposition preferences of two eruptive loopers (Lepidoptera: Geometridae) native to western Canada (western hemlock looper, Lambdina fiscellaria lugubrosa (Hulst), and phantom hemlock looper, Nepytia phantasmaria (Strecker)) for different species and condition of hosts. When offered a choice, phantom hemlock loopers laid nearly three times as many eggs on western hemlock, Tsuga heterophylla (Raf.) Sarg. (Pinaceae) as on either western redcedar, Thuja plicata Donn ex D. Don (Cupressaceae) or western white pine, Pinus monticola Douglas ex D. Don (Pinaceae). Western hemlock loopers were less specific, laying equal numbers of eggs on western hemlock and western redcedar, though fewer eggs were deposited on western white pine when compared with western hemlock. When offered western hemlock trees grown under different nutrient and shading regimes, phantom hemlock loopers preferred to oviposit on high nutrient hosts, irrespective of shading; western hemlock loopers exhibited a preference for high-nutrient hosts only if they were grown without shading. These patterns of host preference can be combined with information regarding forest composition to help quantify the conditional probability of western and phantom hemlock looper distibution and abundance.

Impacts of hemlock looper defoliation on growth and survival of balsam fir, black spruce and white birch in Newfoundland, Canada

Hemlock looper ( Lambdina fiscellaria fiscellaria (Guen.)) is an economically damaging defoliator that undergoes periodic outbreaks in Newfoundland, Canada. It defoliates and causes extensive tree mortality to its primary host, balsam fir ( Abies balsamea [L.] Mill.). We quantified tree survival using data from permanent sample plots (PSPs) and growth reduction or release using dendrochronology, and related these impacts to defoliation severity determined from annual aerial defoliation survey data. Such impact relationships are necessary as a fundamental input to a Decision Support System. Growth and survival of balsam fir, black spruce ( Picea mariana (Mill.) B.S.P.) and white birch ( Betula papyrifera Marsh.) were assessed from 1996 to 2008 in 48 Newfoundland Forest Service PSPs, selected based on four classes of defoliation severity. Two years of severe (71–100%) defoliation resulted in almost complete mortality for balsam fir, 10 years after defoliation, whereas survival was 70–80% for black spruce and white birch. Lower defoliation severity (1–2 years of moderate (31–70%) or 1 year of severe) resulted in approximately 60% survival for balsam fir and no reduction in survival for black spruce and white birch. Maximum growth reduction of balsam fir was 10–15% with 1 year of moderate-severe defoliation, 35–40% with 2 years of moderate defoliation, and about 50% with 2 years of severe defoliation. Growth recovered to pre-defoliation rates 5 years after defoliation ceased in all severity classes. Growth reduction and recovery of black spruce were more variable and lower than for balsam fir, and white birch exhibited only minor (<10%) growth reduction during the defoliation year or 1 year after defoliation. Control measures should focus on avoiding severe defoliation for two consecutive years.

Density‐dependent and density‐independent responses of three species of Telenomus parasitoids of hemlock looper eggs

AbstractWe examined patterns of host exploitation by natural populations of three Telenomus species (Hymenoptera: Scelionidae) parasitizing hemlock looper, Lambdina fiscellaria Guenée (Lepidoptera: Geometridae), eggs in sentinel traps in eastern Quebec and western Newfoundland (Canada). The percentage of eggs parasitized by Telenomus flavotibiae Pelletier and Telenomus coloradensis Crawford in autumn, and by Telenomus droozi Muesebeck in spring either were not or only weakly related to host egg density. In contrast, the percentage of eggs parasitized by T. coloradensis in the spring was positively related to host egg density. Telenomus flavotibiae and T. droozi parasitized eggs in fewer traps than T. coloradensis, suggesting that they were less abundant or less efficient locating host patches. Eggs parasitized by T. droozi only occurred in traps with eggs parasitized by T. coloradensis, suggesting that it may be responding to kairomones emitted by T. coloradensis. In contrast, neither the number nor sex ratio of T. coloradensis emerging from eggs in traps with T. droozi differed from those in traps without this congeneric. Secondary sex ratios of all three species were significantly female biased. Our study suggests that only T. coloradensis has the potential to regulate hemlock looper populations.

Influence of balsam fir (Abies balsamea) budburst phenology on hemlock looper (Lambdina fiscellaria)

Many herbivorous insects emerge synchronously with budburst of their host plant, as the nutritional quality of foliage often decreases rapidly following budburst. We carried out manipulative field experiments to evaluate the influence of bud and shoot phenology on performance of the hemlock looper, Lambdina fiscellaria Guenee (Lepidoptera: Geometridae: Ourapterygini), on balsam fir, Abies balsamea (L.) Mill. (Pinaceae), in NF, Canada. Hemlock looper survival, pupal weight, and realized fecundity, which were then combined to estimate fitness, were all highest when newly emerged first instars were placed on foliage of current-year shoots that had completed approximately 25―35% of their elongation, and lower when placed on younger or older foliage. Survival of a small portion of larvae placed on buds a week before budburst suggests that newly emerged first instars either entered unburst buds or survived for a week without food. In laboratory experiments, approximately half of larvae survived for 4 days without food or water at 10 °C and 65% r.h. The timing of egg hatch in the field appeared to be adaptive, but the short duration of egg hatch suggests that another factor in addition to host plant phenology exerts stabilizing selection pressure on the timing of egg hatch.

Estimating cumulative defoliation of balsam fir from hemlock looper and balsam fir sawfly using aerial defoliation survey in western Newfoundland, Canada

Both hemlock looper (Lambdina fiscellaria fiscellaria (Guen.)) and balsam fir sawfly (Neodiprion abietis (Harris)) undergo periodic outbreaks in eastern Canada and cause significant growth and mortality losses to forests. Tree growth and mortality are closely related to cumulative defoliation estimates, which integrate annual defoliation over multiple years. Our objective was to determine a method to estimate cumulative defoliation of balsam fir (Abies balsamea [L.] Mill) due to these insects in western Newfoundland, using aerial defoliation survey data, as an essential input to modeling impacts for Decision Support Systems. Interpretation of aerial defoliation survey data for hemlock looper and balsam fir sawfly is problematic because both insects feed upon multiple age classes of foliage. Current-year (2008) aerial defoliation survey data were compared with ground estimates of defoliation by age class from 45 plots (450 trees and 395 mid-crown branch samples), representing a range of defoliation severity classes for each insect. Cumulative defoliation was calculated using defoliation per foliage age class, weighted by relative foliage mass for a given age of foliage. Three significantly different severity classes were defined based on cumulative defoliation values derived from aerial defoliation survey: (i) 1-year moderate (30–70%) defoliation, (ii) 1-year severe (71–100%) defoliation with calculated cumulative defoliation values of 19 and 39%, respectively, for balsam fir sawfly, 21 and 34% respectively for hemlock looper; and (iii) 2–3 years of moderate–severe defoliation, with cumulative defoliation ranging between 59 and 64% for balsam fir sawfly and 49% for hemlock looper. Defoliation severity from aerial defoliation survey alone hence can be misleading if defoliation measurements are not converted to cumulative defoliation values.

Seasonal parasitism of hemlock looper (Lepidoptera: Geometridae) eggs in eastern Canada

AbstractA 2-year field study was conducted using sentinel traps to determine the seasonal distribution of the egg parasitoid (Hymenoptera) complex attacking hemlock looper, Lambdina fiscellaria (Guenée), throughout eastern Quebec and western Newfoundland. Hemlock looper populations remained low in all areas over the course of the study. Parasitism of eggs in sentinel traps was generally lower in fall than in spring. Trichogramma Westwood (Trichogrammatidae) as well as Telenomus flavotibiae Pelletier and an unidentified species of Telenomus Haliday (Scelionidae) only parasitized eggs in the fall. Telenomus droozi Muesebeck only parasitized eggs in the spring, whereas T. coloradensis Crawford attacked eggs during both fall and spring. Telenomus coloradensis was the most abundant parasitoid species collected and was far more abundant in spring than in fall collections.

The combined effect of photoperiod and temperature on egg dormancy in an island and a mainland population of the hemlock looper, Lambdina fiscellaria

AbstractEmbryonic dormancy characteristics of the hemlock looper (HL), Lambdina fiscellaria (Guenée) (Lepidoptera: Geometridae), an important coniferous defoliator, were investigated using eggs from an island (Newfoundland) and a mainland (Quebec) population in eastern Canada. We determined (1) the pre‐diapause duration or time required for eggs to change color at 15 °C, under L16:D8 and L12:D12, (2) the percent hatch and time to hatch of early‐diapausing eggs that were, as of 1 September, either (a) incubated under each combination of three photoperiods (L16:D8, L12:D12, or L8:D16) and three temperatures (15, 20, or 25 °C) or (b) stored outdoors prior to their monthly incubation (October–May) under the same treatments, and (3) the diapause duration at 15 °C. The two HL ecotypes completed their pre‐diapause phase in ca. 15 days under long‐day photoperiod. In the mainland ecotype, photoperiod did not influence the pre‐diapause duration. Regardless of photoperiod and ecotype, only eggs incubated continuously at 15 °C hatched successfully after ca. 120 days. Temperature was the most important factor modulating the dormancy of eggs acclimated outdoors, in both ecotypes. From October to December (diapause phase), percent egg hatch at 20 and 25 °C increased from low (20%) to levels similar to those obtained at 15 °C (70%). These percentages remained stable throughout the post‐diapause phase (January–May). Time to hatch, which was shorter at warmer temperatures, decreased from October to December at all temperatures. It remained stable from January to March (quiescence), however, and declined thereafter. Eggs from the island were heavier than those from the mainland and their odds of hatching were 2.3 times higher. At 15 °C, diapause lasted ca. 90 days. Our findings indicate that eggs from the two HL ecotypes (1) undergo an obligatory diapause, (2) complete diapause without pre‐exposure to cold, (3) respond similarly to photoperiod and temperature during diapause and post‐diapause, and (4) do not hatch successfully after prolonged exposure to high temperatures.

Potential Impacts of Climate Change on Western Hemlock Looper Outbreaks

We calculated monthly soil moisture deficits from historical meteorological data from the south coast of mainland British Columbia to quantify warm and dry conditions at monthly and seasonal scales. Our main objective was to determine if climatic conditions antecedent to recorded outbreaks of western hemlock looper (Lambdina fiscellaria lugubrosa Hulst) may have triggered population growth. Periods of soil moisture deficits during the month of June were associated with the onset western hemlock looper outbreaks in the study area, as were warmer and drier conditions during the growing season two years prior to the first year of visible defoliation. Models of climate change predict that future summers in the Pacific Northwest will be warmer and potentially drier than present, and although other factors besides climate influence western hemlock looper population dynamics, the combined effects of more frequent droughts, changes in forest cover, and expanded range of western hemlock due to climate change may result in increased frequency, size and severity of outbreaks in the future.

Daily oviposition pattern of Lambdina fiscellaria (Lepidoptera: Geometridae) under laboratory conditions

AbstractThe hemlock looper, Lambdina fiscellaria, is one of the most economically damaging defoliators of North American coniferous forests. Basic information on its reproductive biology is an essential prerequisite for understanding its population dynamics. Realized fecundity for the two major hemlock looper ecotypes varies along a latitudinal gradient in eastern Canada, but their daily oviposition patterns are similar. Mated females lay eggs after a short pre-oviposition period, with daily oviposition peaking in the first 3 days. Mated females lay significantly more eggs than unmated ones, the latter laying their eggs more evenly throughout their life. Eggs deposited early in the oviposition period are larger than those deposited near the end. This may influence over-winter survival of hemlock loopers and should be considered in studies to better understand the population dynamics and improve management of this defoliator.

Boreal peatland margins as repository sites of long-term natural disturbances of balsam fir/spruce forests

A multidisciplinary, high-resolution paleoecological study (Lepidoptera and plant remains, macroscopic charcoal, pollen) was conducted on a 4000-yr peat monolith extracted from the margin of an ombrotrophic peatland on Anticosti Island (Gulf of St. Lawrence, eastern Canada) to reconstruct the long-term natural disturbances (insect outbreaks, forest fires) of a balsam fir/spruce forest. We hypothesized that an activity of insect defoliators (spruce budworm, hemlock looper) was the main disturbance factor of conifer forests during the Late Holocene. The earliest remains of spruce budworm and hemlock looper were found ca. 3220 and 2350 cal yr BP, respectively. Peaks of insect head capsules occurred from ca. 1640 to ca. 625 cal yr BP. Low balsam fir pollen concentrations during this period suggest a lengthy episode (∼ 1000 yr) of high insect activity, resulting in extensive fir dieback and mortality. The long-term dynamics of the pristine balsam fir/spruce forests were mainly governed by the activity of insect defoliators. The limited extent and possibly the low occurrence of forest fires in the maritime environment of Anticosti Island allowed the development of mature coniferous stands propitious for insect infestations. Insect head capsules appeared to be a useful and effective tool for establishing insect presence and activity during the Holocene.

Host tree age as a selective pressure leading to local adaptation of a population of a polyphagous Lepidoptera in virgin boreal forest

We tested the hypothesis that host tree age may act as a selective factor and lead to local adaptation of the hemlock looper (Lambdina fiscellaria), a geometrid Lepidoptera that has a wide geographical distribution and has evolved in different eco-zones characterized by different levels of floristic composition, age structure and fragmentation level. Considering that hemlock looper outbreaks mainly occurred in old forests, we compared the biological performances of two populations. The first population was collected in the northern virgin boreal forest, which is dominated by mature and overmature coniferous stands that have not suffered from human disturbance. The other population was collected in the southern mixed-wood forest, which is more diversified and has been modified by forest harvesting. Larvae were reared under controlled conditions on foliage from three age classes of balsam fir trees: juvenile, mature and overmature. Although we measured significant variations of biological performances between the two populations, no significant effect of the age of the balsam fir trees could be detected for males from both populations or for females from the southern population. However, northern females were strongly affected by the age of balsam fir trees on which they fed, as their pupal weight was 12% higher and their fecundity increased by 27% on overmature trees compared with juvenile ones. These results indicate that under the same selective pressure, females adapt their strategy to maximize their fitness, and thus they appear as the driving force of evolution through the local adaptation concept. Furthermore, the two populations evolved in distinct habitats and their adaptation reflects selective pressures occurring inside their original environment. This is the first report on local adaptation of an herbivore that is mediated by host tree age. Changes in forest age structure may have a considerable impact on insect local adaptation and presumably on their population dynamics.

Spread and persistence of a rugulosin-producing endophyte in Picea glauca seedlings

We have studied Picea glauca (white spruce) endophyte colonization and its affect on the growth of Choristoneura fumiferana (spruce budworm). Here we examine the spread and persistence of a rugulosin-producing endophyte and rugulosin in needles from trees maintained in the nursery, as well as in trees planted in a test field site. Additionally, we report toxicity of rugulosin against three P. glauca needle herbivores: C. fumiferana, Lambdina fiscellaria (hemlock looper) and Zeiraphera canadensis (spruce budmoth). Reduction in body weight for both the C. fumiferana and L. fiscellaria were observed at 25 and 50 μ m, respectively, and head capsules were reduced at 100 and 150 μ m. Z. canadensis larvae did not perform as well in tests due to an Aspergillus fumigatus infection, but were shown to be lighter when tested with 100 and 150 μ m compared with controls. The endophyte and its toxin were shown to spread throughout the nursery-grown seedlings. After 3.5 and 4.5 y post-inoculation (one and two years in the test site), the inoculated endophyte and its toxin had remained present with an average rugulosin concentration of 1 μg g −1.

Developmental Polymorphism in a Newfoundland Population of the Hemlock Looper, &lt;I&gt;Lambdina fiscellaria&lt;/I&gt; (Lepidoptera: Geometridae)

The hemlock looper [Lambdina fiscellaria (Guenée)], a widespread and highly polyphagous Geometridae, is considered one of the most economically important defoliators of North American coniferous forests. Variations in the number of larval instars between geographic populations of this species have been previously reported in the literature. However, whether such developmental polymorphism occurs within a given population is unknown. In this study, we report the presence of both four and five larval instar individuals within a population of hemlock looper in Newfoundland when reared on balsam fir. For both sexes, the majority of individuals reared on balsam fir shoots went through four larval instars, but more than one third of the females (35.3%) went through five larval instars. Females with four larval instars developed faster and had smaller pupal weight than females with five larval instars. However, a growth-related index (weight gain per unit of time) was similar for the two ecotypes (four or five larval instars). No significant difference was observed between the two ecotypes in terms of reproductive capacity (fecundity and egg size). We also found significant differences in life history traits between males and females. Results indicate that developmental polymorphism, in this case, the variation in the number of larval instars, might provide some adaptive attributes that allowed exploitation of a broader ecological niche.