Do natural enemies explain fluctuations in low-density spruce budworm populations?

Ecology ◽  
2018 ◽  
Vol 99 (9) ◽  
pp. 2047-2057 ◽  
Author(s):  
Mathieu Bouchard ◽  
Véronique Martel ◽  
Jacques Régnière ◽  
Pierre Therrien ◽  
David Laginha Pinto Correia
Keyword(s):  
Natural Enemies ◽  
Spruce Budworm ◽  
Low Density

The influence of hardwood content on balsam fir defoliation by spruce budworm

1996 ◽  
Vol 26 (9) ◽  
pp. 1620-1628 ◽  
Author(s):  
Qiong Su ◽  
Ted D. Needham ◽  
David A. MacLean
Keyword(s):  
New Brunswick ◽  
Natural Enemies ◽  
Spruce Budworm ◽  
Balsam Fir ◽  
Generalized Model ◽  
Stand Management ◽  
Working Hypothesis ◽  
Model Combining

Changing stand composition by increasing hardwood content has been suggested as a long-term method for reducing susceptibility and vulnerability of balsam fir (Abiesbalsamea (L.) Mill.) to spruce budworm (Choristoneurafumiferana (Clem.)). Twenty-five mixed balsam fir–hardwood stands were selected in northern New Brunswick, with five stands in each 20% hardwood class (0–20, 21–40%, etc.). Defoliation each year from 1989 to 1993 was significantly (p < 0.0001) related to hardwood content, with r2 ranging from 0.57 to 0.81. As hardwood content increased, defoliation of balsam fir decreased. From 1989 to 1992, the years of moderate to severe defoliation, balsam fir stands with <40% hardwoods sustained 58–71% defoliation, on average, versus 12–15% defoliation in stands with >80% hardwood. A generalized model combining hardwood content and the estimated defoliation in pure softwood stands in a given year explained 77% of the variation in defoliation over stands and years. This study indicated that mixed balsam fir–hardwood stand management, with hardwood content >40%, could substantially reduce losses during spruce budworm outbreaks. Further research is warranted to elucidate the mechanism involved, but our working hypothesis is that greater hardwood content increased the diversity or populations of natural enemies such as birds and parasitoids.

scholarly journals Dynamics and Management of Rising Outbreak Spruce Budworm Populations

Forests ◽  
2019 ◽  
Vol 10 (9) ◽  
pp. 748 ◽  
Author(s):  
Jacques Régnière ◽  
Barry Cooke ◽  
Ariane Béchard ◽  
Alain Dupont ◽  
Pierre Therrien
Keyword(s):  
Population Growth ◽  
Density Dependence ◽  
Natural Enemies ◽  
Choristoneura Fumiferana ◽  
Regional Scale ◽  
Adult Emergence ◽  
Spruce Budworm ◽  
Migration Activity ◽  
Larval Stages ◽  
The Impact

Management of spruce budworm, Choristoneura fumiferana (Clem.), outbreak spread requires understanding the demographic processes occurring in low, but rising populations. For the first time, detailed observations were made in the early stages of outbreak development. We sampled populations over a three-year period in both treated and untreated populations in the Lower St-Lawrence region of Quebec, Canada, and measured the density-dependence of survival and population growth rates, and the impact of natural enemies and insecticides. Insecticides tested were Bacillus thuringiensis (Berliner 1915) and tebufenozide. We recorded strong density-dependence of survival between early larval stages and adult emergence, explained largely by the variation of natural enemy impacts and overcrowding. We also observed inverse density-dependence of apparent fecundity: net immigration into lower-density populations and net emigration from the higher, linked to a threshold of ~25% defoliation. Because of high migration rates, none of the 2013 treatments reduced egg populations at the end of summer. However lower migration activity in 2014 allowed population growth to be reduced in treated plots. This evidence lends support to the conclusion that, for a budworm population to increase to outbreak density, it must be elevated via external perturbations, such as immigration, above a threshold density of ~4 larvae per branch tip (L4). Once a population has increased beyond this threshold, it can continue growing and itself become a source of further spread by moth migration. These findings imply that populations can be brought down by insecticide applications to a density where mortality from natural enemies can keep the reduced population in check, barring subsequent immigration. While we recognize that other factors may occasionally cause a population to exceed the Allee threshold and reach outbreak level, the preponderance of immigration implies that if all potential sources of significant numbers of moths are reduced on a regional scale by insecticide applications, a widespread outbreak can be prevented, stopped or slowed down by reducing the supply of migrating moths.

Reproductive Biology and Behavior of Tranosema rostrale (Hymenoptera: Ichneumonidae), a Parasitoid of Low-Density Spruce Budworm (Lepidoptera: Tortricidae) Populations

2016 ◽  
Vol 29 (5) ◽  
pp. 500-514 ◽  
Author(s):  
M. Lukas Seehausen ◽  
Myriam Labrecque ◽  
Véronique Martel ◽  
Jacques Régnière ◽  
Amany Mansour ◽  
...  
Keyword(s):  
Reproductive Biology ◽  
Spruce Budworm ◽  
Low Density ◽  
And Behavior

EVALUATION OF SEX ATTRACT ANT TRAPS FOR MONITORING SPRUCE BUDWORM POPULATIONS (LEPIDOPTERA: TORTRICIDAE)

1978 ◽  
Vol 110 (1) ◽  
pp. 43-50 ◽  
Author(s):  
C. J. Sanders
Keyword(s):  
Sex Attractant ◽  
Choristoneura Fumiferana ◽  
Spruce Budworm ◽  
Low Density ◽  
Commercial Sex

AbstractFour commercial sex attractant traps were evaluated for monitoring low density spruce budworm (Choristoneura fumiferana (Clem.)) populations. Factors considered were color, the number of male budworm caught, durability of traps and their ability to exclude non-target insects and debris. The Pherocon 1CP was superior to 3-M Brand Sectar 1 and XC-26; Pherocon 1C was least suitable. Interpretation of the numbers captured may be confounded by the fact that trapped males repel other males.

SAMPLING LOW DENSITY SPRUCE BUDWORM POPULATIONS FOR ISOZYME ANALYSIS

1980 ◽  
Vol 112 (9) ◽  
pp. 969-970 ◽  
Author(s):  
G. T. Harvey
Keyword(s):  
Efficient Method ◽  
Spruce Budworm ◽  
Practical Method ◽  
Isozyme Analysis ◽  
Low Density ◽  
Sticky Traps ◽  
Synthetic Pheromone ◽  
Insect Populations ◽  
Qualitative Changes

A convenient and efficient method of determining if qualitative changes are associated with changes in density of insect populations is to search for changes in isozyme frequencies (Stock and Guenther 1979). However, obtaining sufficient material for analysis of low density populations presents a problem. We have found that the use of sticky traps baited with synthetic pheromone is an efficient and practical method of surmounting this problem.

VARIABLES ASSOCIATED WITH PHEROMONE TRAPS FOR MONITORING SPRUCE BUDWORM POPULATIONS (LEPIDOPTERA: TORTRICIDAE)

1981 ◽  
Vol 113 (6) ◽  
pp. 527-537 ◽  
Author(s):  
Mark W. Houseweart ◽  
Daniel T. Jennings ◽  
C. J. Sanders
Keyword(s):  
Sex Attractant ◽  
Spruce Budworm ◽  
High Density ◽  
Trapping Efficiency ◽  
Low Density ◽  
Pheromone Traps ◽  
Trap Efficiency ◽  
Ca 50 ◽  
Trap Placement

AbstractThe effects of three trap variables (age, saturation, and density) on catches of male spruce budworm moths were tested using Pherocon 1CP® traps baited with synthetic sex attractant in high-density budworm populations in Maine and low-density populations in Ontario. As trap age increased, the number of moths captured decreased significantly; traps aged 2, 10, and 16 days caught an average of 5.4, 28, and 27% fewer moths than unaged traps. Traps functionally saturate and trapping efficiency diminishes in both high and low density populations after ca. 50 moths are caught, although maximum observed catch was 193 moths/day. Density or spacing of traps also affects trap efficiency. Traps spaced 5 m apart may act as a single attraction source. Interference between traps was evident for traps spaced 10, 20, and 30 m apart, while traps spaced at 40 m had the least interference. However, interference at all spacings was noted during peak moth flight in 1978 when mean catch was ca. 140 moths/trap/day.Pherocon 1CP traps can be used for detecting and monitoring spruce budworm populations; however, influences of trap age, timing of trap placement, trap saturation, spacing of traps, and lure strength should be taken into account.

scholarly journals Density Dependence of Egg Recruitment and Moth Dispersal in Spruce Budworms

Forests ◽  
2019 ◽  
Vol 10 (8) ◽  
pp. 706 ◽  
Author(s):  
Jacques Régnière ◽  
Vincent G. Nealis
Keyword(s):  
Population Dynamics ◽  
Boreal Forests ◽  
Random Perturbation ◽  
Spruce Budworm ◽  
Formal Context ◽  
Low Density ◽  
Density Dependent ◽  
Migration Rates ◽  
Net Migration ◽  
And Migration

Egg recruitment quantifies the relative importance of realized fecundity and migration rates in the population dynamics of highly mobile insects. We develop here a formal context upon which to base the measurement and interpretation of egg recruitment in population dynamics of eastern and western spruce budworms, two geographically separated species that share a very similar ecology. Under most circumstances, per capita egg recruitment rates in these budworms are higher in low-density populations and lower in high-density populations, relative to the regional mean: Low-density populations are nearly always migration sinks for gravid moths, and dense populations nearly always sources. The slope of this relationship, measured on a log scale, is negatively correlated with migration rate, and ranges between 0 and −1. The steeper the slope, the more marked net migration. Using our western spruce budworm observations, we found strong evidence of density-dependent emigration in budworms, so migration is not simply a random perturbation in the lagged, density-dependent stochastic process leading to budworm outbreaks. It is itself statistically and biologically density-dependent. Therefore, moth migration is a synchronizing factor and a spread mechanism that is essential to understanding the development and expansion of spruce budworm outbreaks at regional scales in the boreal forests of North America.

scholarly journals Identification of Spruce Budworm Natural Enemies Using a qPCR-Based Molecular Sorting Approach

Forests ◽  
2020 ◽  
Vol 11 (6) ◽  
pp. 621
Author(s):  
Audrey Nisole ◽  
Don Stewart ◽  
George Kyei-Poku ◽  
Marianne Nadeau ◽  
Simon Trudeau ◽  
...  
Keyword(s):  
Natural Enemies ◽  
Choristoneura Fumiferana ◽  
Microscopic Analysis ◽  
Spruce Budworm ◽  
Snp Markers ◽  
Population Cycle ◽  
Larval Rearing ◽  
Species Determination ◽  
Mitochondrial Coi ◽  
Real Time Quantitative Pcr

Annual monitoring of mortality agents in the course of a spruce budworm (Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae)) population cycle is essential to understanding the factors governing the rise and collapse of outbreaks. To date, assessments of causes of budworm mortality have relied on laboratory rearing of field-collected larvae, followed by visual identification of emerging parasitoids and/or microscopic analysis of pathogens in larval carcasses. Although this approach has provided vital information on the abundance and identity of mortality agents, the procedure is labor-intensive and has limits in terms of accuracy. To overcome these shortcomings, we developed a molecular identification tool that makes use of real-time quantitative PCR (qPCR) and TaqMan® technologies. The tool relies on taxon-specific molecular variants (single nucleotide polymorphism [SNP] markers) found in mitochondrial (COI) and nuclear (28S rDNA) genes, for parasitoids, and in the nuclear SSU rDNA gene for microsporidian pathogens; these are then used as molecular signatures targeted by qPCR primers and TaqMan probes. Thus, the design of several sets of primers and probes deployed in multiplex format enables the identification of natural enemies via a molecular sorting process, bypassing barcode sequencing. Crude budworm DNA extracts are processed through a first module that detects dipteran and hymenopteran parasitoids, and microsporidian infections. Positive samples are then processed for species determination using three additional modules, enabling the identification of 20 common natural enemies of the spruce budworm. The tool has been fully validated using DNA samples from all comprised taxa, and both its sensitivity and accuracy compared favorably with the rearing-based method in an analysis of field-collected budworms. Using this tool, sample processing can be completed within two days, does not require larval rearing, provides accurate species identification, and can be conducted by technical staff without extensive molecular biology or insect taxonomy training.

Application of Improved Voltage Compensation in the SEM to Imaging of Organic Materials

1973 ◽  
Vol 31 ◽  
pp. 444-445
Author(s):  
P.J. Killingworth ◽  
M. Warren
Keyword(s):  
Electron Beam ◽  
Organic Materials ◽  
Operating Parameters ◽  
Low Density ◽  
Beam Diameter ◽  
Incident Electron Beam ◽  
Specimen Material ◽  
Voltage Compensation ◽  
Selection Of ◽  
Scanning Electron

Ultimate resolution in the scanning electron microscope is determined not only by the diameter of the incident electron beam, but by interaction of that beam with the specimen material. Generally, while minimum beam diameter diminishes with increasing voltage, due to the reduced effect of aberration component and magnetic interference, the excited volume within the sample increases with electron energy. Thus, for any given material and imaging signal, there is an optimum volt age to achieve best resolution.In the case of organic materials, which are in general of low density and electric ally non-conducting; and may in addition be susceptible to radiation and heat damage, the selection of correct operating parameters is extremely critical and is achiev ed by interative adjustment.

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