Synthesizing selection mosaic theory and host-pathogen theory to explain large-scale pathogen coexistence.

Seven outbreaks of Douglas-fir tussock moth, Orgyia pseudotsugata McDunnough, have recurred in the interior of British Columbia since 1915. But little is known about their impacts on renewable resources in affected stands. A study was undertaken to examine effects of the most recent outbreak on understory vegetation and tree productivity near Kamloops, British Columbia. Dry weight forage production was sampled from 1m² circular plots under various levels of stand crown cover (0-96%) and density (0-45.9m²/ha), as modified by defoliation. Crown cover was determined using a moosehorn, and from vertical photographs obtained with a 160° lens mounted on a conventional camera. Stand density was determined using a 20 factor prism. Increment cores were obtained at breast height, and radial growth analysed under the Addo-X. Ring width behaviour was compared with occurrence of past outbreaks. The ecological literature on 0. pseudotsugata was reviewed. Negligible amounts of forage were obtained from many plots with undefoliated trees. In defoliated plots with live trees, total forage production ranged from 0.0 under 96% crown cover and 45.9 m²/ha density to 648.9 kg/ha under 50% crown cover and 16.0 m²/ha density. The average yield in small openings was 3667.4 kg/ha. High variability was evident. In one stand, two years following its defoliation and consequent death, total forage yields exceeded those from nearby small openings. Forage yield data were described better by logarithmic models than by hyperbolic ones, at 95% probability. Impacts on tree growth were not demonstrable one year following defoliation. Many trees recovered even from complete defoliation. Insect outbreaks and periods of slow tree growth coincided, but quite inconsistently. Apparently, most scattered infestation patches develop independently of each other. Grazing values should increase in seriously defoliated stands even without range seeding. On poor sites and in stands managed primarily for forage production, outbreaks of 0. pseudotsugata may be left alone without necessarily endangering remote stands. Selective control favoring better sites managed for tree production should improve efficiency of investing scarce funds in protection of the inventory. Tree growth and insect outbreaks may be under the influence of some regional climatic factor, but local factors are also important. A need remains for long term impact studies on tree growth, forage yield and nutrient status, and other resources.

Integrated pest management of the Douglas-fir tussock moth

Impact of the first recorded outbreak of the Douglas-fir tussock moth, Orgyia pseudotsugata, in southern California and the extent of its distribution in the Pacific Southwest region

Dosage-mortality studies with commercial Bacillus thuringiensis sprayed in a modified Potter's tower against some forest insects

Outbreaks of the Douglas-fir tussock moth, Orgyia pseudotsugata (McDunnough), have recurred periodically, at 7- to 10-year intervals, since the first recorded observation in 1916 in Chase, British Columbia, Canada. Anderson and May (1981) hypothesized that microparasites are responsible for the periodic population fluctuations of some defoliating insects. We chose the association between the Douglas-fir tussock moth and a viral disease, caused by a nuclear polyhedrosis virus (NPV), to test whether their model, and variants thereof, can predict the observed population cycles. Density-dependent mortality, vertical transmission of the virus and an incubation period were added to the free-living stages model of Anderson and May (1981). Parameter values for the models were derived from published data and from an experiment.Sensitivity analyses conducted for each model showed that none of the models generated the behavior of the Douglas-fir tussock moth as observed in the field. Thus, the periodicity of the outbreaks in field populations of tussock moths cannot be explained solely by the dynamics of the viral disease as described by Anderson and May's class of models; the virus is too short-lived and the growth rate of the insect population too high. Dynamics of other system components such as predators, parasites or food of the tussock moth probably play a significant role in the insect's population dynamics.

Tussock moths of the family Lymantriidae are an important group of forest defoliators that characteristically have periodic outbreaks. The sex pheromone of the female Douglas-fir tussock moth, Orgyia pseudotsugata (McDunnough), has been identified as (Z)-6-heneicosen-11-one (Smith et al. 1975) and shown to be sexually stimulating to males of seven tussock moth species in two genera, Orgyia and Dasychira (Daterman et al. 1976; Grant 1977). Laboratory tests demonstrated that this compound could disrupt mating of both the whitemarked tussock moth,O. leucostigma (J.E. Smith), and rusty tussock moth, O. antiqua (L.), when the adults were maintained in an atmosphere containing the chemical (Grant and Frech 1976). Subsequently field tests in small plots treated with the same material released into the atmosphere at a rate equivalent to 20-50 mg/ha/day demonstrated that pheromone communication of whitemarked tussock moths and a conifer-feeding tussock moth, Dasychira plagiata (Walker), could be disrupted in their natural habitat (Grant 1978). Similar disruption was obtained with field populations of the Douglas-fir tussock moth (Sower and Daterman 1977). The present report describes the disruptive effects of (Z)-6-heneicosen-11-one in the field on the pheromone communication of another species, the rusty tussock moth.

This study compares the effects of separate Douglas-fir tussock moth (Orgiapseudotsugata McDunnough) and western spruce budworm (Choristoneuraoccidentalis Freeman) infestations on the radial growth of two host species, grand fir (Abiesgrandis (Doug.) Lindl.) and Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco). Growth records from nonhost species were also examined to substantiate that growth reduction in the hosts resulted from feeding by the respective defoliators. Ring-width data, standardized to remove trends of decreasing width from pith to bark, were tested statistically to identify significant differences in the effects of each defoliator on each host species. Four measures of radial growth were examined: maximum rate of growth decline, average rate of growth recovery, 1-year growth loss, and 5-year growth loss. The effects of tussock moth did not differ statistically between host species, but the impact of budworm defoliation on grand fir was significantly greater than on Douglas-fir. Differences occurred between the overall effects of tussock moth and budworm on the host species, with tussock moth causing significantly more rapid growth reductions and greater growth losses than budworm. It is concluded that (1) grand fir and Douglas-fir ring patterns, individually or in combination, can provide good evidence of severe defoliation by Douglas-fir tussock moth, (2) grand fir ring patterns can be used to identify severe defoliation by western spruce budworm, and (3) Douglas-fir ring patterns can provide evidence of budworm infestation only if corroborative evidence of a budworm infestation is present in the ring patterns of grand fir trees in the same stand.

An outbreak of the Douglas-fir tussock moth, Orgyia pseudotsugata McDunnough, occurred in the South Platte River drainage on the Pike-San Isabel National Forest in the Colorado Front Range attacking Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco. Stocking levels, species composition, and tree size in heavily and lightly defoliated stands were similar. Douglas-fir tussock moth defoliation resulted in significant Douglas-fir mortality in the heavily defoliated stands, leading to a change in dominance to ponderosa pine, Pinus ponderosa Lawson. Douglas-fir beetle, Dendroctonus pseudotsuqae Hopkins, populations increased following the defoliation event but caused less mortality, and did not differ between heavily and lightly defoliated stands. Douglas-fir tussock moth-related mortality was greatest in trees less than 15 cm dbh (diameter at 1.4 m above the ground) that grew in suppressed and intermediate canopy positions. Douglas-fir beetle-related mortality was greatest in trees larger than 15 cm dbh that grew in the dominant and co-dominant crown positions. Although both insects utilize Douglas-fir as its primary host, stand response to infestation is different. The extensive outbreak of the Douglas-fir tussock moth followed by Douglas-fir beetle activity may be associated with a legacy of increased host type growing in overstocked conditions as a result of fire exclusion.

Although the importance of insect viruses in the population dynamics of their hosts is widely acknowledged, ecologists are still relatively ignorant of the factors determining the rate of transmission of insect viruses in the field. I performed a series of field experiments in which I investigated the transmission dynamics of the nuclear poly— hedrosis virus (NPV) of Douglas—fir tussock moth, Orgyia pseudotsugata (Lepidoptera: Lymantriidae), in northern Idaho, USA. In these experiments, I reared healthy and infected healthy larvae that became infected as a measure of transmission. I explored the influences of density, stage structure, and spatial structure on transmission by manipulating the density and stage distribution of healthy and infected hosts, and the spatial distribution of infected hosts. The experiments indicate that transmission is strongly affected by the densities of both healthy and infected hosts, but the effect depends on the instar of each. Late instars are both more infectious and more likely to become infected than are early instars, so that the NPV is more likely to spread in populations of late—instar tussock moth larvae. I also found that transmission is affected by the spatial distribution of infected hosts, and this effect also depends on the instar of healthy hosts. That is, transmission to healthy early instars decreases with increasing patchiness of infected hosts, but transmission to healthy late instars is essentially unaffected by patchiness. I discuss how these results can be in— terpreted in terms of behavioral differences among instars, and relate the results to the mathematical theory of disease and the use of viruses in biological pest control.

the eastern United States (Cottam and Higgins, 1946; Nelson and Surber, 1947), but none has been reported in the forested areas of western United States. During May, 1947, 413,500 acres of forest were sprayed with DDT in oil solution to control an epidemic of tussock moth (Hemerocampa pseudotsugata) in northern Idaho. In July and August, four plots were sprayed in northwestern Wyoming in an experimental attempt to control mountain pine beetle (Dendroctonus monticolae). The spraying was done by airplane under the supervision of the Forest Service and the Bureau of Entomology and Plant Quarantine. These projects gave an opportunity to study the effects of DDT on the fish and wildlife. In Idaho, forests in the western foothills of the Bitterroot Mountains near Moscow were sprayed at the rate of one pound of DDT per acre. The trees principally affected by the tussock moths were Douglas fir (Pseudotsuga taxifolia) and grand fir (Abies grandis). The vegetative habitat also included western white pine (Pinus monticola), ponderosa pine (Pinus ponderosa), western red cedar (Thuja plicata), lodgepole pine (Pinus contorta), and associated species. There was generally a heavy understory of several kinds of shrubs such as willow (Salix sp.), snowberry (Symphoricarpos racemosus), Oregon grape (Odostemon aquifolium), serviceberry (Amelanchier alnifolia), and Menziesia (Menziesia ferruginea). There were more than fifty streams in the treated area including the Palouse River, Potlatch Creek, Elk Creek, and their tributaries.

Bacillus thuringiensis Cry1A toxin-binding glycoconjugates present on the brush border membrane and in the peritrophic membrane of the Douglas-fir tussock moth are peritrophins

Constraint-based models have become popular methods for systems biology as they enable the integration of complex, disparate datasets in a biologically cohesive framework that also supports the description of biological processes in terms of basic physicochemical constraints and relationships. The scope, scale, and application of genome scale models have grown from single cell bacteria to multi-cellular interaction modeling; host-pathogen modeling represents one of these examples at the current horizon of constraint-based methods. There are now a small number of examples of host-pathogen constraint-based models in the literature, however there has not yet been a definitive description of the methodology required for the functional integration of genome scale models in order to generate simulation capable host-pathogen models. Herein we outline a systematic procedure to produce functional host-pathogen models, highlighting steps which require debugging and iterative revisions in order to successfully build a functional model. The construction of such models will enable the exploration of host-pathogen interactions by leveraging the growing wealth of omic data in order to better understand mechanism of infection and identify novel therapeutic strategies.

Much of the dynamics of coevolution may be driven by the interplay between geographic variation in reciprocal selection (selection mosaics) and the homogenizing action of gene flow. We develop a genetic model of geographically structured coevolution in which gene flow links coevolving communities that may differ in both the direction and magnitude of reciprocal selection. The results show that geographically structured coevolution may lead to allele-frequency clines within both interacting species when fitnesses are spatially uniform or spatially heterogeneous. Furthermore, the results show that the behavior and shape of clines differ dramatically among different types of coevolutionary interaction. Antagonistic interactions produce dynamic clines that change shape rapidly through time, producing shifting patterns of local adaptation and maladaptation. Unlike antagonistic interactions, mutualisms generate stable equilibrium patterns that lead to fixed spatial patterns of adaptation. Interactions that vary between mutualism and antagonism produce both equilibrium and dynamic clines. Furthermore, the results demonstrate that these interactions may allow mutualisms to persist throughout the geographic range of an interaction, despite pockets of locally antagonistic selection. In all cases, the coevolved spatial patterns of allele frequencies are sensitive to the relative contributions of gene flow, selection, and overall habitat size, indicating that the appropriate scale for studies of geographically structured coevolution depends on the relative contributions of each of these factors.

The Douglas-fir tussock moth (Orgyia pseudotsugata McDunnough) defoliated Douglas-fir (Pseudotsuga menziesii var glauca [Beissn.] Franco), in British Columbia from 1981 to 1983. Forty-five defoliated and 16 non-defoliated (check) plots were monitored for defoliation and damage from 1982 to 1985. By 1985, cumulative mortality and top-kill in the defoliated plots averaged 51% (49% by volume) and 11%, respectively. Check plots sustained no mortality and less than 1% top-kill due to causes other than tussock moth defoliation. Mortality occurred very early in the outbreak, with 56% of the dead trees already dead by 1982, generally after 1 year, but at most after 2 years of defoliation. Mortality and top-kill were related to the number of seasons of defoliation and, particularly, to defoliation intensity. It was concluded that Douglas-fir tussock moth is an important depletion factor of Douglas-fir in British Columbia.

Reductions in ring width of Douglas-fir, Pseudotsuga menziesii [Mirb.] Franco, trees defoliated for 1 year by the Douglas-fir tussock moth, Orgyia pseudotsugata (McDunnough), are reported. Trees were treated with a nuclear polyhedrosis virus, but the resultant epizootic which killed larvae and reduced defoliation took several weeks to develop and trees sustained varying degrees of damage. No negative effects of defoliation were noted in the year when feeding took place; on the contrary, a growth stimulation occurred. Defoliation levels above 50% resulted in growth reduction for 2 years following defoliation relative to nondefoliated trees. The implications of these growth changes for cost/benefit analysis of control options are discussed. For. Sci. 37(3):959-964.