Spruce Budworm Moths Research Articles

Characterizing eastern spruce budworm’s large-scale dispersal events through flight behavior and stable isotope analyses

Eastern spruce budworm moth (Choristoneura fumiferana (Clem.)) mass outbreaks have widespread economic and ecological consequences. A key explanation for the large-scale spread and synchronization of these outbreaks is the long-distance dispersal (up to 450 km) of moths from hotspots (high-density populations) to lower-density areas. These events have proved difficult to monitor because dispersal flights occur only a few times a year, have no consistent routes, and commonly used tracking methods (e.g., population genetics, mark-recapture, radio telemetry) are inadequate for this system. Confirming immigration and distinguishing between local and immigrant individuals are crucial steps in identifying the physical and ecological drivers of moth dispersal. Here, we test whether isotopes of hydrogen (i.e., delta notation: δ2H) and strontium (i.e., strontium isotope ratios: 87Sr/86Sr), known to independently vary in space in a predictable manner, can be used to show that an immigration event occurred and to distinguish between local and immigrant adult spruce budworm moths. We used an automated pheromone trap system to collect individuals at six different sites in eastern Canada within and outside the current outbreak area of budworm moths. We first use moth flight behavior and time of capture, currently the best available tool, to determine putative local vs. immigrant status, and then evaluate whether individual 87Sr/86Sr and δ2H differ between putative classes. At two sites, we detect immigrant individuals that differ significantly from putative locals and thus confirm immigration has occurred. Saliently, sites where putative locals were sampled before the occurrence of potential immigration events (~10 days) showed the strongest differences between immigrant individuals’ and local 87Sr/86Sr and δ2H values. Sites where the collection of putative locals was close in time (hours) or following an immigration event (days) had a less-clear distinction between putative immigrants and locals, and showed signs of mixing between these two groups. We speculate that recent immigration could have led to the misclassification of immigrants as putative locals. 87Sr/86Sr and δ2H data generally support the adequacy of current approaches using capture-time to detect immigration events, and provide enhanced resolution to distinguish between local and immigrant individuals and to confirm an immigration event. We discuss the broader implication of adding isotopes to the toolkit to monitor spruce budworm dispersal and suggest next steps in implementing these tools.

Modeling weather-driven long-distance dispersal of spruce budworm moths (Choristoneura fumiferana). Part 1: Model description

Long-term studies of insect populations in the North American boreal forest have shown the vital importance of long-distance dispersal to the maintenance and expansion of insect outbreaks. In this work, we extend several concepts established previously in an empirically-based dispersal flight model with recent work on the physiology and behavior of the adult eastern spruce budworm (SBW) moth, Choristoneura fumiferana (Clemens). An outbreak of defoliating SBW in Quebec, ongoing since the mid-2000s, already covers millions of hectares of forests in eastern Canada and threatens to spread into neighboring areas through annual summertime episodes of long-distance dispersal. Such flight events in favorable conditions frequently include billions of SBW moths dispersing in the warm atmospheric boundary layer, typically starting around sunset and often lasting through several hours of wind-driven transport over hundreds of kilometers. Successful SBW dispersal to possibly distant host forest areas depends acutely on the weather. Here we describe the components and results of SBW–pyATM, an open-source individual-based modeling framework developed in Python for the simulation of these weather-driven SBW dispersal events. Using seasonal SBW phenology results from BioSIM at known outbreak locations and high-resolution Weather Research and Forecasting (WRF) model output, we focus on modeling dispersal flights over two successive nights in July 2013 in southern Quebec. Our flight model closely reproduces the SBW spatial patterns and motions observed by weather surveillance radar over the St. Lawrence estuary. With SBW–pyATM we can estimate landing locations for both male and female SBW and the resulting spatial patterns of egg distribution, allowing us eventually to forecast future larval defoliation activity in new locations where immigration could help overcome local limitations on SBW populations. This information could then support forest management decisions where SBW outbreaks threaten valuable resources.

Circadian rhythms of insect pheromone titer, calling, emission, and response: a review.

Many insect species have circadian rhythms of pheromone production/titer, calling, emission, and response that are involved in intraspecific communication and impact pest management practices. Rhythms of pheromone biosynthesis, most studied in moths affecting forestry and agriculture, contribute to a periodicity of pheromone concentration or titer within glands or hemolymph. Calling rhythms by the pheromone-emitting sex are physical movements (pumping, vibrating wings) that aid in release and dispersion of the volatile pheromone components attractive to the opposite conspecific sex or both sexes. Circadian rhythms of emission of pheromone also occur as a result of an interaction between calling and the titer of pheromone available for release. Responding individuals usually show a coincidental rhythm of dispersal flight while seeking pheromone plumes in which, by orienting upwind, the insects find mates or food resources. However, some species begin searching an hour or more before the emitting sex initiates calling and emission, which benefits mass trapping control programs because the baited traps do not compete initially with natural pheromone sources. In our review, data of daily rhythms of moths and other insects were extracted from the literature by screen capture software to calculate mean time of activity and standard deviation and fit to normal curves. These methods are illustrated for various insects and as a basis for discussion of interactions of pheromonal circadian rhythms of the well-studied gypsy moth Lymantria dispar, spruce budworm moth Choristoneura fumiferana, turnip moth Agrotis segetum, and cabbage looper moth Trichoplusia ni. The various circadian rhythms are discussed in relation to application of species-specific sex and aggregation pheromones for benign biological control and management of pest insects.

Tracking insect outbreaks: a case study of community-assisted moth monitoring using sex pheromone traps

Insect outbreaks can cover vast geographic areas making it onerous to cost-effectively monitor populations to address management or ecological questions. Community science (or citizen science), which entails engaging the public to assist with data collection, provides a possible solution to this challenge for the spruce budworm ( Choristoneura fumiferana Clemens), a major defoliating pest in North America. Here, we lay out the Budworm Tracker Program, a contributory community science program developed to help monitor spruce budworm moths throughout eastern Canada. The program outsources free pheromone trap kits to volunteers who periodically check and collect moths from their traps throughout the budworm flight period, then return them in a prepaid envelope to the organizers. Over three years, the program engaged an average of 216–375 volunteers and yielded a data return rate of 68%–89%, for a total of 16 311–54 525 moths per year. Volunteer retention among years was 71%–89%. Data from this program offer compelling evidence for the range of long-distance moth dispersal. Although our program was designed for spruce budworm, this template could easily be adapted for forestry, urban forestry, and agricultural systems to monitor any of the numerous organisms for which there is an established trapping method.

Modeling Migratory Flight in the Spruce Budworm: Temperature Constraints

We describe an individual-based model of spruce budworm moth migration founded on the premise that flight liftoff, altitude, and duration are constrained by the relationships between wing size, body weight, wingbeat frequency, and air temperature. We parameterized this model with observations from moths captured in traps or observed migrating under field conditions. We further documented the effects of prior defoliation on the size and weight (including fecundity) of migrating moths. Our simulations under idealized nocturnal conditions with a stable atmospheric boundary layer suggest that the ability of gravid female moths to migrate is conditional on the progression of egg-laying. The model also predicts that the altitude at which moths migrate varies with the temperature profile in the boundary layer and with time during the evening and night. Model results have implications for the degree to which long-distance dispersal by spruce budworm might influence population dynamics in locations distant from outbreak sources, including how atmospheric phenomena such as wind convergence might influence these processes. To simulate actual migration flights en masse, the proposed model will need to be linked to regional maps of insect populations, a phenology model, and weather model outputs of both large- and small-scale atmospheric conditions.

The Impact of Moth Migration on Apparent Fecundity Overwhelms Mating Disruption as a Method to Manage Spruce Budworm Populations

Aerial applications of a registered formulation of synthetic spruce budworm female sex pheromone were made in 2008, 2013 and 2014 to disrupt mating in populations of this forest insect pest in Quebec, Canada. Each year, the applications resulted in a 90% reduction in captures of male spruce budworm moths in pheromone-baited traps. A commensurate reduction in mating success among virgin females held in individual cages at mid-crown of host trees was also obtained. However, there was no reduction in the populations of eggs or overwintering larvae in the following generation (late summer and fall). The failure of this approach as a viable tactic for spruce budworm population reduction could have resulted from considerable immigration of mated females, as evidenced by high rates of immigration and emigration that caused steep negative relationships between apparent fecundity and the density of locally emerged adults.

Effects of tebufenozide on the assemblage of moths (Lepidoptera) in an operational spruce budworm (Lepidoptera: Tortricidae) suppression programme

AbstractTebufenozide (Mimic) kills Lepidoptera larvae that ingest it. Aerial applications of tebufenozide were made against spruce budworm (Choristoneura fumiferana(Clemens)) (Lepidoptera: Tortricidae) in boreal forest in Manitoba, Canada, in 1999 and 2000. In 2000 and 2001, moths in sprayed and unsprayed plots were sampled with light traps; trapping was supplemented by foliage sampling. Relative to unsprayed plots, catches of spruce budworm moths in plots sprayed in 1999 and 2000 were depressed in 2000, but not in 2001. Host tree defoliation was reduced in 2000 by 1999 and 2000 applications; the 2000 application reduced numbers of spruce budworm larvae in 2000 and 2001. Multivariate analysis revealed negative effects of tebufenozide application on two species of non-target moths in 2000 and no negative effects in 2001. Negatively affected species have larvae feeding in the tree canopy at the time of spray application. Higher catches of non-target species in sprayed treatments were observed for three species in 2000 and two species in 2001. We conclude that tebufenozide can depress the numbers of spruce budworm larvae and provide foliage protection during the year of application and the following year, and that negative effects on non-target species are detectable for about 15 months after application.

Comparative Modeling of Two Special Scenarios of Extreme Dynamics in Forest Ecosystems: Psillides in Australia and Spruce Budworm Moth in Canada

Critical states of quantity remain outside the framework of classical methods of mathematical modeling in ecology. Outbreaks disrupt the idea of a species balance with the environment, the hypothesis of competition between individuals of one population and a decrease in reproduction efficiency with increasing density. In modern conditions, the extreme dynamics of populations take place more often due to the penetration of alien species into ecosystems and expansion of its areal. Explosive reproductions cause serious damage to the forest industry and can even irreversibly transform the environment. By the method of comparative analysis of situations, it is considered two scenarios of rapid, but spontaneously damped outbreaks of forest pests. For the dynamics of psyllides in the forests of Australia, a hybrid model with transition to chaotic fluctuations is proposed. Spruce budworm moth Choristoneura fumiferana in Canada is characterized by a series of damped peaks. The proposed model in the form of equations with delay describes the scenario of damped sharp oscillations, which has a more general character. A similar dynamics can be traced for invasive ctenophore Mnemiopsis leidyi in the Caspian Sea and even in the dynamics of the epidemic of the "Spanish flu" a century ago, according to mortality in the UK. The scenarios considered in new computing models are transitional processes in the interaction of the species with its biotic environment.

Behaviors of Western Spruce Budworm Moths (Choristoneura occidentalis) as Defences Against Bat Predation

We investigated potential defense behaviors of adult western spruce budworm (Choristoneura occidentalis), a non-auditive lepidopteran, against bat predation. Although western spruce budworm moths started to fly before sunset, earlier than many species of moths, temporal isolation of flying moths from foraging bats was incomplete as moths were most active after sunset once bats were foraging. Flying C. occidentalis were most active close to their host trees, and thus were isolated from some bat activity because vegetation limits foraging by some bats. Moths mostly flew near the tops of trees, an area that may have a high predation pressure from bats. Resting western spruce budworm spent little time fluttering their wings or crawling, behaviors that are used as cues by gleaning bats. The outbreak nature of this species, in which large numbers of moths are active at one time, may allow dilution effects to reduce predation risk.

Oviposition Behavior of the Eastern Spruce Budworm Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae)

We documented 13 behaviors associated with oviposition in unfertilized and fertilized spruce budworm moths, Choristoneura fumiferana, by videotaping active moths with a macro lens. Apart from resting, the most pronounced behaviors were probing, drumming + probing, and egg laying. Probing was a bending of the abdomen and extension of the ovipositor to touch the substrate in a rocking, back and forth motion. Drumming + probing involved tapping of the substrate with the pro- and mesothocacic legs with concurrent bending of the abdomen as above. Egg laying was the actual process of egg deposition onto the needle surface of a balsam fir twig. Both the frequency and the duration of these behavioral elements varied depending on the mating status of the female. Unfertilized females exhibited a higher frequency of probing and egg laying. The duration of probing was longer in unfertilized females, while drumming + probing and egg laying were longer for fertilized females. This study is the basis for future work on the chemosensilla associated with the perception of host-plant surface chemicals by ovipositing females.

EFFECT OF PHEROMONE PERMEATION ON SUSTAINED FLIGHT OF MALE SPRUCE BUDWORM

AbstractFlight durations of male spruce budworm moths, Choristoneura fumiferana (Clem.), that were locked-on to pheromone plumes from female moths were measured in a wind tunnel. Flight was sustained by use of a movable patterned ceiling. The longest sustained flight was 53 min. The effects of different background concentrations of synthetic pheromone were tested by surrounding the female moths with rubber septa loaded with synthetic pheromone. The duration of sustained flights decreased as the concentration of background synthetic pheromone increased, but at all concentrations some males persisted in orientated flight for 10 min or longer.

EFFECTS OF PROLONGED EXPOSURE TO DIFFERENT CONCENTRATIONS OF SYNTHETIC PHEROMONE ON MATING DISRUPTION OF SPRUCE BUDWORM MOTHS IN A WIND TUNNEL

AbstractMale spruce budworm moths were kept in a wind tunnel for 4 days and assayed each day to determine their ability to locate calling females that were surrounded by rubber septa loaded with synthetic pheromone, a 95:5 blend of E:Z-11-tetradecenal. As the concentration of synthetic pheromone increased, the numbers of males successfully locating females decreased, the latency of response increased, and the speed of flight decreased. At release rates from the septa close to those of a calling female, 6–60 ng/h per septum, most disrupted males flew to a septum instead of the females. At the highest release rate tested, 600 ng/h, many males were inactive or flew to the sides of the tunnel, which indicates sensory fatigue. This effect was more pronounced among males that were continuously exposed to the synthetic pheromone for the 4 days than among males kept in pheromone-free air between assays. About a quarter of the males died or became unable to fly after the 4 days, but there was no change in the proportions of the different responses of males, or in their response times, with increasing age, nor was there evidence that males were conditioned by their experience on previous days. The results led to the conclusion that time-averaged atmospheric concentrations of the synthetic pheromone as high as 20 ng/m3 are necessary to achieve effective disruption of the orientation of male spruce budworm moths to calling female moths.

Biotechnology in forestry: Examples from the Canadian Forest Service

As a general trend, research activities related to biotechnology in the Canadian Forest Service (CFS) have increased significantly during the last decade as illustrated by a marked increase in resources committed to this field and in the number of publications produced by the scientists involved. The three areas covered by CFS biotechnological activities are forest regeneration, forest protection and environmental impact assessment. In forest regeneration, the tissue culture of conifers using somatic embryogenesis is a good example of potential application of biotechnology to conventional tree improvement. This technology is being used on a large scale in British Columbia and involves private firms such as BC Research Inc. Other technologies are also being developed such as genetic engineering which eventually will allow the incorporation of advantageous traits into trees which would otherwise be difficult or impossible to achieve. In forest protection, Bacillus thuringiensis is a well known success of biotechnology. This bacterium is used as a biopesticide in Canada to control spruce budworm and gypsy moth. Its use has been increasing during the last few decades and, with the phasing out of chemical insecticides for forestry use, Bacillus thuringiensis will become one of the few alternatives available for insect control. Insect viruses are also becoming more attractive for the biological control of forest pests. The CFS has registered three viruses for forestry use and the next generation of viruses will be genetically engineered to increase their efficiency and effectiveness. The last area of activity encompasses environmental impact studies of biotechnology products for forestry use. The CFS has been a pioneer in the development of microcosms (soil and aquatic) for studying microbial pesticides used to evaluate the impact of engineered biopesticides. Key words: biotechnology, genetic engineering, biopesticides, molecular biology, tissue culture, microcosm, regulation, environmental impact

Disruption of male spruce budworm orientation to female moths by pheromone and pheromone analogues in a wind tunnel

Abstract. The ability of male spruce budworm moths, Choristoneura fumiferana (Clem.), to orientate to and locate virgin female moths was investigated in a laboratory wind tunnel. When presented with two caged ‘target female’ moths, more than 99% of the male moths locked on and flew directly to the females. When confined for 3 h before release, downwind of a three‐dimensional array of thirty‐five evenly distributed female moths (a density of 40/m3), over 90% of the males still successfully oriented to one or another of the females, although not always to the target females. With an array of thirty‐five septa containing either E‐11‐tetradecenyl acetate on E‐11‐tetradecenol there was no visible change in behaviour; >90% of the males flew directly to the two target females, which indicates that neither the acetate nor the alcohol has potential for mating disruption. An array of thirty‐five septa containing a 955 blend of E‐ and Z‐11‐tetradecenal, the main components of the spruce budworm sex pheromone, significantly reduced the numbers of male moths able to locate the target females, and effects were concentration‐dependent. The highest concentration, which gave a release rate similar to that of a calling female, produced the same level of disruption as the thirty‐five females, but sensory fatigue became a factor in addition to ‘false trail following’. Lower concentrations were significantly less effective, with no evidence of sensory fatigue. At all concentrations significant numbers of males flew to the septa (false trail following), but when male moths were left uncaged in the tunnel for a further 3h, most eventually located the females. This suggests that false trail following alone will not prevent mating. The level of disruption was not improved by the addition of 2% tetradecanal to the 955 blend. Similar levels of disruption to the 955 blend were obtained with an 80:20 blend. A 5050 blend still caused a significant amount of false trail following, but less than the other blends. The ability of male spruce budworm to orientate to off‐blend trails was enhanced if the males were first exposed to the natural, female‐produced pheromone.

The locomotory response of the egg parasitoid Trichogramma evanescens Westwood to hexane extracts of eastern spruce budworm scales (Choristoneura fumiferana (Clemens))

The response of Trichogramma evanescens Westwood to various concentrations of hexane extracts from the scales of one of its hosts, the spruce budworm moth (Choristoneura fumiferana (Clemens)), was investigated. When placed on filter papers treated with hexane extracts of the moth scales, the wasps responded with two distinct phases of intensified searching behaviours. The first was characterized by a rapidly induced, transient klinokinetic response (decreased walking speed) lasting 10–20 s. This response had an abrupt threshold at scale extract concentrations between 0.05 and 0.5 mg/mL. After 15 s of exposure walking speeds subsequently recovered to rates similar to those of wasps walking on areas treated with hexane only (control). The second behaviour consisted of a persistent orthokinetic response (increased number of abrupt turns, greater than 70°), which resulted in the wasps remaining longer in the test arena. This increased retention on the patch was observed for extract concentrations below 0.05 mg/mL and appeared to be at least partially independent of changes in wasp velocity. Several parameters evaluated, including mean velocity, mean angular change, and fractal dimension, were highly variable within and between treatment groups, and showed no consistent pattern of response with dosage. In contrast, time spent on the patch and total distance travelled on the test area showed a significant correspondence to the dosage-dependent orthokinetic response of the wasps.

FACTORS AFFECTING CATCH IN PHEROMONE TRAPS FOR MONITORING THE WESTERN SPRUCE BUDWORM, CHORISTONEURA OCCIDENTALIS FREEMAN

AbstractThe effects of trap design, lure concentration, lure age, and trap maintenance on the catch of western spruce budworm moths, Choristoneura occidentalis Freeman, in pheromone traps were tested in light to moderate infestations near Ashcroft, B.C. High cumulative moth catches reduced the trapping efficiency of both the sticky traps and the non-sticky Uni-traps relative to traps from which the moths were removed every 2 days. Correlations between the total season’s catch and larval density per plot in the same and following generations were not significant (P>0.05) for any of the eight combinations of trap design, lure concentration, and maintenance regimen tested. However, by dividing the mean moth catch in Uni-traps by either the basal area or foliage biomass per hectare in each plot, correlations with the following year’s larval density were significant (r2 = 0.77–0.98; P<0.05; n=5).

Detection of mesoscale synoptic features associated with dispersal of spruce budworm moths in eastern Canada

Radar studies in eastern Canada of spruce budworm moth distribution patterns and associated windfields frequently revealed mesoscale synoptic features induced by the strong thermal contrast between the heated land surface and the surrounding coastal waters that resulted in significant redistribution of the airborne moths. Experience gained during a four-year study in New Brunswick enabled meteorologists to identify the synoptic situations favouring the development of these mesoscale features. This paper examines the details of a particular case, on 15-16 July 1976, when insect detection teams were alerted in advance to the existence and location of a significant wind convergence zone.

FLIGHT DURATION OF MALE SPRUCE BUDWORM (CHORISTONEURA FUMIFERANA [CLEM.]) AND ATTRACTIVENESS OF FEMALE SPRUCE BUDWORM ARE UNAFFECTED BY MICROSPORIDIAN INFECTION OR MOTH SIZE

AbstractNo correlation was found between the size of male spruce budworm (Choristoneura fumiferana [Clem.]) moths and the duration of their flight in a sustained-flight wind tunnel. The numbers of male moths caught in traps baited with virgin female spruce budworm moths increased as the size of the females increased, but the relationship was significant in only one of eight experiments. Infection with the microsporidium Nosema fumiferanae (Thomson) resulted in smaller insects, but there were no significant relationships between the incidence of infection and male flight duration or female attractiveness.

Differences in oxidase and esterase activities involved in pheromone biosynthesis in two species ofChoristoneura

The released pheromone and the glandular lipids, labeled with [(14)C]acetate, were analyzed fromChoristoneura orae andChoristoneura fumiferana budworm moths by thin-layer chromatography and autoradiography. Radiolabeled lipids in the gland appeared to be identical in the two moths with both insects containing high amounts of 11-tetradecenyl acetates. In contrast, theC. orae moths released primarily labeled acetate ester and alcohol, and the spruce budworm moths (C. fumiferana) labeled aldehyde consistent with the known composition of their respective pheromones. The levels of the enzymes responsible for converting the acetate ester into aldehyde were found to be significantly lower in gland extracts fromC. orae moths than fromC. fumiferana moths. These results implicate an acetate esterase and an alcohol oxidase in controlling the composition of the pheromone blend released from closely related budworm species.

Roles of minor components in pheromone-mediated behavior of western spruce budworm male moths

The behavior of male western spruce budworm moths,Choristoneura occidentalis Freeman, was observed in a flight tunnel in response to virgin females and synthetic sex pheromone components, alone and in blends. Pheromone blends were also compared in the field using sticky trap bioassays. Pheromones were incorporated into small rods of polyvinyl chloride. The blend of 92∶8 (E/Z)-11-tetradecenal-89∶11 (E/Z)-11-tetradecenyl acetate-85∶15 (E/Z)-11-tetradecenol (Ald∶Ac∶OH) that approximated that released from a virgin female moth elicited levels of response similar to those elicited by the female. This blend induced a significantly greater percentage of moths to fly upwind and land at the lure than did the Ald lure. In contrast to the flight-tunnel bioassays, the numbers of moths caught in Ald-baited sticky traps in the field were not significantly increased by the addition of Ac and OH lures. The net upwind groundspeed of flight in response to the 0.05% Ald lure was lower than that in response to the virgin females and was significantly increased by the addition of Ac + OH lures in two of three bioassays. The flight-tunnel bioassays support the hypothesis that the natural blend of major (Ald) and minor (Ac + OH) components stimulates the precopulatory behavior of western spruce budworm male moths at long range (> 1 m downwind) as well as at close range.