Using Simple Models to Predict Virus Epizootics in Gypsy Moth Populations

Dwyer, Greg; Elkinton, Joseph S.

doi:10.2307/5477

Cited by 143 publications

(163 citation statements)

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“…Despite the traditional assumptions of constant transmission rates, it has been shown empirically for a number of parasite systems that transmission rates are not independent of the density of hosts and/or infectious units (Dwyer & Elkinton 1993;D'Amico et al . 1996;Knell, Begon & Thompson 1996;Dwyer, Elkinton & Buonaccorsi 1997;Knell, Begon & Thompson 1998a).…”

Section: Introductionmentioning

confidence: 99%

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Parasite transmission: reconciling theory and reality

Fenton

Fairbairn

Norman

et al. 2002

Journal of Animal Ecology

117

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Summary 1.Arguably the most important and elusive component of host-parasite models is the transmission function. Considerable empirical and theoretical work has focused on determining the correct formulation of this function although, to date, there has been little attempt to combine these studies to develop general insights into how observed transmission rates affect host-parasite dynamics. 2. Here, estimates of transmission rates from a range of host-parasite systems in the literature are described using a phenomenological function which takes into account how transmission varies with host and parasite densities. This function is placed in the appropriate model framework to determine the consequences of the observed transmission rates for each system. 3. All of the parasites had decreasing per capita transmission rates with increasing parasite densities suggesting that parasites tend to saturate at high densities, either as hosts become limiting or due to heterogeneities amongst the host population. In terms of the responses to host density, the parasites fell into two groups: those with increasing or decreasing transmission rates. This dichotomy was due to the biology of the organisms; the former group infect through cannibalism, which increased at high densities as the individuals became stressed, whereas the latter group infected through free-living stages, resulting in a form of spatial structuring reducing the number of hosts available for infection. 4. A metapopulation model was developed where hosts and parasites interacted in discrete patches according to the appropriate transmission function, with neighbouring patches linked by dispersal. The model suggested that small-scale, localized transmission events can drive large-scale epizootics at the metapopulation level. This emphasizes the importance of correctly describing and quantifying the transmission function at the individual level. 5. Traditionally, the formulation of the transmission function has depended on the scale of observation. This work shows that transmission should be considered from the viewpoint of the organisms concerned. Observed transmission rates are a consequence of the biology of the individuals meaning it should be possible to develop a priori hypotheses concerning the nature of the transmission function from a basic understanding of the life history of the organisms concerned.

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Section: Introductionmentioning

confidence: 99%

“…Laboratorybased or small-scale field experiments, which consider transmission close to the individual scale, have looked for non-linearities in the transmission rate with changing densities (Dwyer & Elkinton 1993;D'Amico et al . 1996;Knell et al .…”

Section: Introductionmentioning

confidence: 99%

Parasite transmission: reconciling theory and reality

Fenton

Fairbairn

Norman

et al. 2002

Journal of Animal Ecology

117

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“…Understanding how symbiosis is maintained in natural populations requires, perhaps most importantly, an understanding of how symbionts are transmitted throughout host populations and the factors that influence individual transmission events [1,2]. Classic and contemporary models of transmission typically focus on the factors that operate at the level of the host population and influence the frequency of dispersal opportunities for symbionts such as host contact rates and symbiont prevalence.…”

Section: Introductionmentioning

confidence: 99%

A symbiont's dispersal strategy: condition-dependent dispersal underlies predictable variation in direct transmission among hosts

2015

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Direct horizontal transmission of pathogenic and mutualistic symbionts has profound consequences for host and symbiont fitness alike. While the importance of contact rates for transmission is widely recognized, the processes that underlie variation in transmission during contact are rarely considered. Here, we took a symbiont's perspective of transmission as a form of dispersal and adopted the concept of condition-dependent dispersal strategies from the study of free-living organisms to understand and predict variation in transmission in the cleaning symbiosis between crayfish and ectosymbiotic branchiobdellidan worms. Field study showed that symbiont reproductive success was correlated with host size and competition among worms for microhabitats. Laboratory experiments demonstrated high variability in transmission among host contacts. Moreover, symbionts were more likely to disperse when host size and competition for microhabitat created a fitness environment below a discrete minimum threshold. A predictive model based on a condition-dependent symbiont dispersal strategy correctly predicted transmission in 95% of experimental host encounters and the exact magnitude of transmission in 67%, both significantly better than predictions that assumed a fixed transmission rate. Our work provides a dispersalbased understanding of symbiont transmission and suggests adaptive symbiont dispersal strategies can explain variation in transmission dynamics and complex patterns of host infection.

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“…This becomes important when considering specific control scenarios. For instance, the presence of an active host-seeking stage means that transmission rates may be higher than those of microparasites, where b has been estimated to be nearer to Ϫ12 d Ϫ1 (Dwyer and Elkinton 1993;Goul-2 # 10 son et al 1995;D'Amico et al 1996) than to Ϫ7 d Ϫ1 , 2 # 10 as was estimated for entomopathogenic nematodes here.…”

Section: Discussionmentioning

confidence: 83%

Evaluating the Efficacy of Entomopathogenic Nematodes for the Biological Control of Crop Pests: A Nonequilibrium Approach

Fenton

Norman

Fairbairn

et al. 2001

The American Naturalist

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. The University of Chicago Press andThe American Society of Naturalists are collaborating with JSTOR to digitize, preserve and extend access to The American Naturalist.http://www.jstor.org abstract: The efficacy of entomopathogenic nematodes for biological control is assessed using deterministic models. Typically, the examination of such models involves stability analyses to determine the long-term persistence of control. However, in agricultural systems, control is often needed within a single season. Hence, the transient dynamics of the systems were assessed under specific, shortterm control scenarios using stage-structured models. Analyses suggest that preemptive application may be the optimum strategy if nematode mortality rates are low; applying before pest invasion can result in greater control than applying afterward. In addition, repeated applications will suppress a pest, providing the application rate exceeds a threshold. However, the period between applications affects control success, so the economic injury level of the crop and the life history of the pest should be evaluated before deciding the strategy. In all scenarios, the most important parameter influencing control is the transmission rate. These findings are applicable to more traditional biological control agents (e.g., microparasites and parasitoids), and we recommend the approach adopted here when considering their practical use. It is concluded that it is essential to consider the specific crop and pest characteristics and the definition of control success before selecting the appropriate control strategy. One aspect that has received considerable attention in the last 10 yr is the incorporation of explicit stage structuring in the insect-host population (Murdoch et al. 1987;Godfray and Waage 1991;Godfray 1995a, 1995b;Murdoch and Briggs 1996). Such stage structuring, in the form of coupled delay-differential equations, enables greater biological detail to be described by a few, intuitively defined parameters while maintaining a degree of analytical tractability.However, despite the increased realism of this new generation of models, it may be that, at least in terms of evaluating biological control success, they are not being used to address the pertinent questions. In recent years, a number of authors have drawn attention to the fact that long-term stability rarely has any bearing on the practical success of a control program (Murdoch et al. 1985;Kareiva 1990;Hastings 1999), although the vast majority of models continue to evaluate control success in these terms. We contend that such models of "intermediate complexity" can be used to answer specific, practical questions concerning biological control while ...

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Using Simple Models to Predict Virus Epizootics in Gypsy Moth Populations

Cited by 143 publications

References 39 publications

Parasite transmission: reconciling theory and reality

Parasite transmission: reconciling theory and reality

A symbiont's dispersal strategy: condition-dependent dispersal underlies predictable variation in direct transmission among hosts

Evaluating the Efficacy of Entomopathogenic Nematodes for the Biological Control of Crop Pests: A Nonequilibrium Approach

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