A 4-year research project on 'Evaluating Environmental Risks of Biocontrol Introductions in Europe' (ERBIC) is described, and early results are presented. The project focuses on arthropod biological control (using both microbial and macrobial agents), and uses literature review, case studies with empirical work and various types of modelling to illuminate risk to non-target organisms. These methods will hopefully lead to the development of usable methodologies and guidelines for risk assessment in arthropod biological control, by the project's completion in 2002. Reviewing existing published and unpublished data on the classical biological control of insects (a first step in this project) has revealed that for only 1.5% of introductions is there some data regarding the realized field specificity of the agent. For a tiny proportion of introductions there are quantitative data regarding mortality in non-targets. From these cases, with some extrapolation, we can deduce that 10% or less of classical biological control introductions in the past led to population changes in non-targets. Data on population-level effects from simulated uses or trials suggest that 49% of inundative or augmentative uses of agents led to (local, short-term) population changes for non-targets. Case studies into: (i) exotic specialist parasitoids used in the greenhouse; (ii) exotic generalist parasitoids used inundatively in the field; (iii) exotic generalist predators used inundatively; and (iv) fungi and nematodes used as bioinsecticides, are outlined. The results so far demonstrate: (i) the apparent safety of Trichogramma (generalist parasitoid) releases in Switzerland, despite rare species within its host range; (ii) the lack of overwintering capability in northern Italy in one generalist predator (Orius insidiosis), but its presence in another (Harmonia axyridis); (iii) little evidence that the predation of certain stages of native predators by introduced predators will enhance environmental risks in the cases in question; and (iv) the apparent safety of bioinsecticide releases of particular pathogen strains for important naturally occurring predators when exposed directly or by feeding on infected prey.
Summary 0[ The population dynamic e}ects of refuges\ which hosts enter and leave by di}usive movement\ in hostÐparasitoid interactions are explored using simple models in con! tinuous time[ 1[ This type of refuge has a stabilizing e}ect on a hostÐparasitoid interaction\ which is contrary to the implications of some previous models[ 2[ Stability can be explained by considering how depletion processes lead to a refuge proportion "proportion of hosts protected at a given instant# that increases as para! sitoid density increases[ This e}ect is synonymous with pseudointerference in the context of the model[ 3[ Very high rates of movement of host larvae largely destroy this stability process[ Stability is greatest at intermediate levels of movement[ 4[ Density!dependent host movement can alter the e}ect of these refuges such that they are either more stabilizing\ or tend to destabilize\ the dynamics of hostÐparasitoid systems\ depending on the type of density dependence assumed[ The conclusion that intermediate movement rates are likely to generate stability with this general type of refuge is not altered in the presence of any type of density dependence\ unless the density dependence is at levels which we consider unrealistically high and unlikely to be encountered in nature[ 5[ It is the assumption that larvae do not move into the refuge prior to becoming vulnerable to parasitism that ensures top!down population control in the model[ Thus\ parasitoids attacking very early instars make good candidates for biological control when faced with a structural refuge[
The biocontrol of insect pests may pose a risk to native insects if the biocontrol agent attacks nontarget species. Potential biocontrol agents are screened before release to determine their acceptance of nontarget species and the suitability of nontarget species for their development. Here we show that, even though a biocontrol agent has very low acceptance of a nontarget species, it may nonetheless have a large impact on the nontarget population. This impact does not require the nontarget species to be a suitable prey capable of supporting the biocontrol agent population, but instead may be a transient impact that occurs soon after the agent is released. Because the population of biocontrol agents is likely to increase rapidly in response to the high density of its target pest, the resulting high density of the agent population may dominate its low acceptance of the nontarget species, causing a strong decline or even local extirpation of the nontarget. We demonstrate this possibility using models of host-parasitoid dynamics that incorporate a broad range of assumptions about the life histories of hosts and parasitoids, and that demonstrate how various common aspects of host-parasitoid biology are likely to reduce this risk considerably. The predictions of the models are reasonably approximated with a simple formula, which potentially provides a simple method for assessing the risk of transient impacts, but which should only be applied loosely (in a qualitative manner) and in the context of a fuller understanding of other factors affecting risk in the system in question.
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