Introduction Of Biological Control Agents Research Articles

Complex Habitats Boost Predator Co-Occurrence, Enhancing Pest Control in Sweet Pepper Greenhouses

Sweet pepper is a crop that benefits from phytosanitary treatments with low environmental impact, especially the successful control of pests through the introduction of biological control agents in greenhouses. However, predators that naturally occur in these surroundings often enter greenhouses. The precise roles of these natural predators and their interactions with the introduced predatory insects and mites are often unknown. This study investigated the relationships between Nesidiocoris tenuis, which is naturally present, and Amblyseius swirskii and Orius laevigatus, which are two species of generalist predators released for the control of multiple pests. This study was conducted for two years on 13 commercial sweet pepper crops in various types of greenhouses (tunnels and traditional greenhouses) in Sicily. The environmental complexity value (ECV) for each site was estimated based on 18 points detected around the site according to the different habitats that occurred at each coordinate. The results showed that the occurrence of N. tenuis in greenhouses, independently of their typology (tunnel or traditional greenhouse), was mainly promoted by the greater diversification of habitats immediately surrounding the pepper crops (in a circular area with a diameter of 500 mt), with an increase in its density during the crop season. Moreover, N. tenuis–O. laevigatus’s co-occurrence in flowers suggested that they were not impacted by each other’s presence and that their co-occurrence had a significant effect on pest reduction, although their co-occurrence was density-dependent. As an intraguild predator, N. tenuis competed with O. laevigatus for Frankliniella occidentalis when many predators were present. In addition, N. tenuis also competed with A. swirskii when they both occurred in flowers at a higher density. This study highlights the importance of pepper plant flowers in promoting a higher occurrence of juvenile forms of N. tenuis within flowers. Amblyseius swirskii colonized the plants in 3 weeks, distributing itself almost uniformly over the leaves with a clear control action against not only Bemisia tabaci but also F. occidentalis when present on the flowers. Thus, this concurrent analysis of several commercial pepper sites within the same production area suggests that, even with similar pest control plans, the diverse variability in the presence of natural enemies must be considered when selecting control strategies for pepper crop pests and that N. tenuis, favored by complex surrounding habitats, contributes actively to pest reduction.

When a plant invader meets its old enemy abroad: what can be learnt from accidental introductions of biological control agents.

Accidental introductions of biological weed control (BWC) agents (i) offer opportunities to assess host use of agents with a potentially broader fundamental host-range than those approved for field release directly in target areas; (ii) urge national authorities to rapidly respond as they may threaten native species or crops, and by this (iii) help advancing post-release studies, a neglected aspect of BWC. Through detailed insights gained from studying the recent accidental introduction of the ragweed leaf beetle Ophraella communa into Europe, we derive suggestions for overcoming barriers to adoption of BWC by re-evaluating the predictive power of pre-release studies and, thus, the presently strict criteria for deciding upon their release that might exclude safe and efficient agents. By using the allergenic weed Ambrosia artemisiifolia and the accidentally introduced BWC agent O. communa as study system, we also hope to raise the awareness of authorities to consider biological control more prominently as a key approach for pest management in the 'One Health' concept, which aims to sustainably balance and optimize the health of people, animals, plants and ecosystems. © 2023 Society of Chemical Industry.

Biological Control of Plant Diseases: An Evolutionary and Eco-Economic Consideration.

Biological control is considered as a promising alternative to pesticide and plant resistance to manage plant diseases, but a better understanding of the interaction of its natural and societal functions is necessary for its endorsement. The introduction of biological control agents (BCAs) alters the interaction among plants, pathogens, and environments, leading to biological and physical cascades that influence pathogen fitness, plant health, and ecological function. These interrelationships generate a landscape of tradeoffs among natural and social functions of biological control, and a comprehensive evaluation of its benefits and costs across social and farmer perspectives is required to ensure the sustainable development and deployment of the approach. Consequently, there should be a shift of disease control philosophy from a single concept that only concerns crop productivity to a multifaceted concept concerning crop productivity, ecological function, social acceptability, and economical accessibility. To achieve these goals, attempts should make to develop “green” BCAs used dynamically and synthetically with other disease control approaches in an integrated disease management scheme, and evolutionary biologists should play an increasing role in formulating the strategies. Governments and the public should also play a role in the development and implementation of biological control strategies supporting positive externality.

Biology, Ecology, and Pest Management of the Tarnished Plant Bug, Lygus lineolaris (Palisot de Beauvois) in Southern Row Crops.

Simple SummaryThe tarnished plant bug, Lygus lineolaris, is a polyphagous, sap-feeder that causes significant economic damage in several field crops, especially cotton (Gossypium hirsutum L.) in the mid-southern United States. In 2020, it was reported that 4.8 million acres of cotton were infested by Lygus spp. in the United States. A broad host range, polyphagous feeding behavior and high mobility of this pest along with resistance development to conventional pesticides helped them establish as a significant pest of concern for cotton growers in the mid-south. Since the publication of a review by Layton (2000) on damage caused by Lygus lineolaris, many new research studies have been published on the Lygus biology, ecology, and integrated pest management strategies. A comprehensive review paper that summarizes these latest research developments and Lygus management strategies will be useful for researchers and cotton growers. In this review, we report and discuss the latest developments in Lygus research and the new control strategies that have been developed in the last two decades.The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), (Hemiptera: Miridae) is considered the most damaging pest of cotton (Gossypium hirsutum L.) in the mid-southern United States, although it is established throughout the United States, southern Canada, and northern Mexico. The introduction of transgenic crops for the control of moths in the Heliothine complex and eradication of the boll weevil, Anthonomus grandis, from much of the United States led to greatly reduced pesticide use in cotton fields, which allowed L. lineolaris to emerge as a new primary pest of cotton in the mid-southern United States. Since the publication of a review by Layton (2000) on damage caused by Lygus lineolaris, many new studies have been published on the changes in host range, population dynamics, sampling methods and thresholds, cultural practices, sex pheromones and attractant blends, novel pesticides and insecticide resistance mechanisms, olfactory and feeding behaviors, introduction of biological control agents, host-plant resistance mechanisms, and new molecular and genetic tools for integrated pest management of Lygus species in cotton and other important crops. Here, we review and discuss the latest developments in L. lineolaris research in the last two decades.

Irradiation-induced sterility in an egg parasitoid and possible implications for the use of biological control in insect eradication

Classical biological control is a pest control tool involving the release of imported natural enemies. The Sterile Insect Technique (SIT) comprises releasing sexually sterile insects of a pest into the wild population for suppression or eradication. Both these approaches are environmentally friendly and their combination can result in a synergistic impact on pest populations and improve eradication. However, stringent regulation surrounding the introduction of biological control agents limits their use in eradication owing to the perceived risk of effects on non-target organisms. We investigated the irradiation biology of the egg parasitoid Trissolcus basalis to ascertain whether sterile parasitoids could mitigate the risk of potential sustained non-target impacts. Mated female T. basalis were gamma-irradiated at doses between 120 and 150 Gy and exposed to egg masses of their host Nezara viridula throughout their lifespans. This resulted in host mortality, despite a substantial reduction in developing parasitoid offspring, which followed a negative dose–response. There was no emergence of parasitoid offspring at 140 Gy and above. Irradiation did not affect oviposition behaviour but caused an increase in longevity. Consequently, sterile parasitoids could possibly alleviate concerns regarding the irreversibility of biological control release, which promotes further investigation of their potential role in eradication.

The influence of two wildfires and biological control agents on the population dynamics of Melaleuca quinquenervia in a seasonally inundated wetland

AbstractThe potential of Melaleuca quinquenervia (Cav.) S.T. Blake to reinvade cleared areas was evaluated over a 13-yr period that included two wildfires and the introduction of biological control agents. The first wildfire occurred in 1998 and was followed by a mean of 591.5 recruited seedlings m−2. Recruits from that fire were cleared 7 yr later in July 2005 for a second experiment to evaluate seedling recruitment into cleared areas. Seed rain, seedling recruitment and mortality, and sapling growth rates were measured in four plots located around individual large reproductive trees. A second natural wildfire in 2007 burned through those plots, leading to increases in seed rain followed by a pulse in recruitment of 21.04 seedlings m−2, 96.5% fewer than after the 1998 fire. Recruits in half of the plots around each tree were then treated with regular applications of an insecticide to restrict herbivory by biological control agents, while herbivory was not restricted in the other half. There was no difference in seedling mortality between treatments 1,083 d post-fire (2007) with 96.6% seedling mortality in the unrestricted herbivory treatment and 89.4% mortality in the restricted herbivory treatment. Recruits subjected to the restricted herbivory treatment grew taller than those in the unrestricted herbivory treatment, 101.3 cm versus 37.4 cm. Many of the recruits were attacked by the biological control agents, which slowed their growth. Although solitary M. quinquenervia trees retain some capacity to reinvade areas under specific circumstances, there was a downward trend in their overall invasiveness at this site, with progressively smaller recruitment cohorts due to biological control agents. Land managers should prioritize removing large reproductive trees over treating recently recruited populations, which can be left for many years for the biological control agents to suppress before any additional treatment would be needed.

Divergence in Photoperiod Responses of a Classical Biological Control Agent, Galerucella calmariensis (Coleoptera: Chrysomelidae), Across a Climatic and Latitudinal Gradient.

A key knowledge gap in classical biological control is to what extent insect agents evolve to novel environments. The introduction of biological control agents to new photoperiod regimes and climates may disrupt the coordination of diapause timing that evolved to the growing season length in the native range. We tested whether populations of Galerucella calmariensis L. have evolved in response to the potential mismatch of their diapause timing since their intentional introduction to the United States from Germany in the 1990s. Populations collected from 39.4° to 48.8° latitude in the western United States were reared in growth chambers to isolate the effects of photoperiod on diapause induction and development time. For all populations, shorter day lengths increased the proportion of beetles that entered diapause instead of reproducing. The critical photoperiods, or the day length at which half of a population diapauses, differed significantly among the sampled populations, generally decreasing at lower latitudes. The latitudinal trend reflects changes in growing season length, which determines the number of generations possible, and in local day lengths, at the time when beetles are sensitive to this cue. Development times were similar across populations, with one exception, and did not vary with photoperiod. These results show that there was sufficient genetic variation from the two German source populations to evolve different photoperiod responses across a range of environmental conditions. This study adds to the examples of rapid evolution of seasonal adaptations in introduced insects.

Post-release genetic assessment of two congeneric weed biological control agents

Introductions of biological control agents are unique field experiments to examine the response of novel organisms to new environments. Post-release monitoring is particularly challenging where closely related and morphologically similar biological control agents have been released. Two closely-related phytophagous weevils, Larinus minutus and L. obtusus, were introduced as biological control agents for two major rangeland weeds, diffuse knapweed, Centaurea diffusa and spotted knapweed, C. stoebe subsp. micranthos in North America. The release of the Larinus species coincided with a decline in C. diffusa abundance in many areas. However, it was not clear whether both species of Larinus had become established as they are morphologically very similar. We asked: (1) Could genetic markers be used to identify both the weevil species? (2) Do both weevil species attack both knapweed species in Canada? (3) Are the levels of genetic diversity of the introduced populations of the weevils similar to those of a European source population? (4) Is genetic mixing between the weevil species occurring? Both microsatellite and CO1 mtDNA markers distinguish between the two weevil species. Larinus obtusus was only found on spotted knapweed, while L. minutus was more widely distributed and attacked both weed species. The relatively large initial introductions of weevils to British Columbia (4,300 L. minutus and 5,500 L. obtusus) together with rapid population growth and frequent redistribution among sites has been sufficient to maintain levels of genetic diversity. Results from small samples showed that haplotype, nucleotide diversity and allelic richness of the introduced populations were comparable to those of a European population. We found no evidence for hybridization in the introduced populations.

Genetic evidence for plural introduction pathways of the invasive weed Paterson's curse (Echium plantagineum L.) to southern Australia.

Paterson’s curse (Echium plantagineum L. (Boraginaceae)), is an herbaceous annual native to Western Europe and northwest Africa. It has been recorded in Australia since the 1800’s and is now a major weed in pastures and rangelands, but its introduction history is poorly understood. An understanding of its invasion pathway and subsequent genetic structure is critical to the successful introduction of biological control agents and for provision of informed decisions for plant biosecurity efforts. We sampled E. plantagineum in its native (Iberian Peninsula), non-native (UK) and invaded ranges (Australia and South Africa) and analysed three chloroplast gene regions. Considerable genetic diversity was found among E. plantagineum in Australia, suggesting a complex introduction history. Fourteen haplotypes were identified globally, 10 of which were co-present in Australia and South Africa, indicating South Africa as an important source population, likely through contamination of traded goods or livestock. Haplotype 4 was most abundant in Australia (43%), and in historical and contemporary UK populations (80%), but scarce elsewhere (< 17%), suggesting that ornamental and/or other introductions from genetically impoverished UK sources were also important. Collectively, genetic evidence and historical records indicate E. plantagineum in southern Australia exists as an admixture that is likely derived from introduced source populations in both the UK and South Africa.

Weed biological control in the Greater Mekong Subregion: status and opportunities for the future.

Abstract The status of weed biological control in the six Greater Mekong Subregion (GMS) countries was assessed, and opportunities to develop biological control in the region are proposed. Twenty biological control agents targeting nine weed species have been introduced into GMS countries, with 13 agents establishing on seven weed species. Another nine biological control agents have spread unintentionally into the region. These agents are having a slight to high impact on their target weeds. However, the number of weeds in the region that have been targeted for biological control is only a fraction of the number of weeds (45) in the region that have been targeted for biological control elsewhere. This presents a tremendous opportunity to expand weed biological control in the region and reduce the dependency on herbicides while increasing productivity. There are numerous highly effective biological control agents present elsewhere that could be introduced to assist with the management of the region's most important weeds, such as Pistia stratiotes , Salvinia molesta , Chromolaena odorata and Mikania micrantha . Along with the introduction of biological control agents, there is also a scope to increase the capacity and training in biological control within GMS countries to develop effective weed control and management.

Weed biological control in the European Union: from serendipity to strategy

Biological control of weeds is a globally recognised approach to the management of some of the most troublesome invasive plants in the world. Accidental introductions of agents accounted for all weed biological control agent establishments in the European Union until 2010, but these examples include some current or emerging control successes both large and small, from the redistribution of the weevil Stenopelmus rufinasus Gyllenhal (Coleoptera: Curculionidae) for the control of small outbreaks of Azolla filiculoides Lam. (Azollaceae), to the large scale control provided by the cochineal insect Dactylopius opuntiae (Cockerell) (Hemiptera: Dactylopiidae), used against some problematic prickly pears (Opuntia spp. (Cactaceae)), and the ragweed beetle Ophraella communa LeSage (Coleoptera: Chrysomelidae), against common ragweed, Ambrosia artemisiifolia L. (Asteraceae), which are providing benefits to an increasing number of Member States of the European Union. Recent programmes involving the intentional introduction of biological control agents against target weeds including Fallopia japonica (Hout.) Ronse Decr. (Polygonaceae), Impatiens glandulifera Royle (Balsaminaceae) and Acacia longifolia (Andrews) Willd (Fabaceae) show a shift from luck to judgement in the European Union. The inclusion of new weed targets on the European Invasive Species Regulation should lead to a growth in the profile and use of biological control which would be assisted by the publication of any successes from the few intentional introductions covered in this paper.

Shifting paradigms in the history of classical biological control

Classical biological control using insects has led to the partial or complete control of at least 226 invasive insect and 57 invasive weed species worldwide since 1888. However, at least ten introductions of biological control agents have led to unintended negative consequences and these cases have led to a focus on risk that came to dominate the science and practice of classical biological control by the 1990s. Based upon historical developments in the field we consider that the era of focus on benefits began in 1888 and that it was supplanted by an era in which the focus was on risks during the 1990s. This paradigm shift greatly improved the safety of biological control releases but also led to a decline in the number of introductions, probably resulting in opportunity costs. We note here the development of a third paradigm: one in which the benefits and risks of biological control are clearly and explicitly balanced so that decisions can be made that maximize benefits while minimizing risks.

Ecology of forest insect invasions

Forests in virtually all regions of the world are being affected by invasions of non-native insects. We conducted an in-depth review of the traits of successful invasive forest insects and the ecological processes involved in insect invasions across the universal invasion phases (transport and arrival, establishment, spread and impacts). Most forest insect invasions are accidental consequences of international trade. The dominant invasion ‘pathways’ are live plant imports, shipment of solid wood packaging material, “hitchhiking” on inanimate objects, and intentional introductions of biological control agents. Invading insects exhibit a variety of life histories and include herbivores, detritivores, predators and parasitoids. Herbivores are considered the most damaging and include wood-borers, sap-feeders, foliage-feeders and seed eaters. Most non-native herbivorous forest insects apparently cause little noticeable damage but some species have profoundly altered the composition and ecological functioning of forests. In some cases, non-native herbivorous insects have virtually eliminated their hosts, resulting in major changes in forest composition and ecosystem processes. Invasive predators (e.g., wasps and ants) can have major effects on forest communities. Some parasitoids have caused the decline of native hosts. Key ecological factors during the successive invasion phases are illustrated. Escape from natural enemies explains some of the extreme impacts of forest herbivores but in other cases, severe impacts result from a lack of host defenses due to a lack of evolutionary exposure. Many aspects of forest insect invasions remain poorly understood including indirect impacts via apparent competition and facilitation of other invaders, which are often cryptic and not well studied.

Assessing Probabilistic Risk Assessment Approaches for Insect Biological Control Introductions.

The introduction of biological control agents to new environments requires host specificity tests to estimate potential non-target impacts of a prospective agent. Currently, the approach is conservative, and is based on physiological host ranges determined under captive rearing conditions, without consideration for ecological factors that may influence realized host range. We use historical data and current field data from introduced parasitoids that attack an endemic Lepidoptera species in Hawaii to validate a probabilistic risk assessment (PRA) procedure for non-target impacts. We use data on known host range and habitat use in the place of origin of the parasitoids to determine whether contemporary levels of non-target parasitism could have been predicted using PRA. Our results show that reasonable predictions of potential non-target impacts may be made if comprehensive data are available from places of origin of biological control agents, but scant data produce poor predictions. Using apparent mortality data rather than marginal attack rate estimates in PRA resulted in over-estimates of predicted non-target impact. Incorporating ecological data into PRA models improved the predictive power of the risk assessments.

Evolution of biological control agents following introduction to new environments

The introduction of biological control agents (BCAs) creates the potential for adaptive evolution in translocated organisms. BCAs are confronted with new environments that can promote adaptation to exploit novel resources, even within short ecological time frames. In particular, insect BCAs are amenable to rapid evolution due to their short generation times and relatively large population sizes. These factors hypothetically increase the likelihood that, when exposed to novel habitats, environmental selection could cause BCAs to extend their range to non-target host species. Alternatively, insects may simply extend their range as their generalist or polyphagous habits are fully realized. In this review, we consider recent literature that addresses these topics. Adaptations to environmental conditions have been demonstrated in a number of BCAs. Mechanisms of adaptation include founder effects, hybridization, and endosymbiosis. Yet, there is little evidence of adaptive host range expansions among insect and weed biological control agents to non-target species, albeit existing examples are from limited numbers of studies. Important future directions and current developments in the field incorporate next generation sequencing technology that can promote better resolution of population divergence, possible mechanisms involved in adaptation to novel resources, and insect hybridization. Future studies should also include a careful consideration of the influence of microbes on BCA efficacy and environmental adaptation.

The unpredictable risk imposed by microbial secondary metabolites: how safe is biological control of plant diseases?

Currently, a strong public and political demand for reducing chemical pesticides exists, supporting strengthening of biological plant protection programs in agriculture. Biological plant protection strategies largely depend on introducing antagonistic microorganisms to agro-ecosystems. This approach would indeed reduce the impact of synthetic chemistries and may help avoiding development of fungicide-resistant pathogen populations, but on the other hand may strongly increase the load of microbial toxins. In crops treated with biological control agents, neither the newly forming (confronting) microbial communities nor the secondary metabolites synthesized by these are known. Many microbial secondary metabolites may not only exhibit acute toxicities significantly exceeding those of fungicides, but even act as strong carcinogens. This paper discusses the risks imposed by the introduction of biological control agents and strongly suggests including secondary metabolite gene cluster expression data into the list of information required for approving any plant protection agents and releasing them to the field. Secondary metabolism gene expression data could strongly support assessing the risk imposed by microorganisms used in disease and pest control.

Predation rates of mixed instar Odonata naiads feeding on Aedes aegypti and Armigeres moultoni (Diptera: Culicidae) larvae

In Thailand, several important diseases are transmitted by mosquitoes. Many vector control programs focus on the reduction of these medically important mosquitoes through the application of pesticides, bed-nets and the introduction of biological control agents. Odonates naiads are important, naturally occurring predators of vector mosquitoes. To estimate the predation rates of odonate species in Thailand, we conducted an experiment in which the predation rates were compared across a range of predator and prey densities. We used seven different predator species from different instars that represented the composition of naiads in our study area. Body sizes ranged between 2.6mm and 15.9mm. Two different prey species were used, larvae of the mosquito Armigeres moultoni Edwards, 1914 and Aedes aegypti L. 1762. Predation rates showed a positive non-linear relationship with prey densities and a negative non-linear relationship with predator densities. The mean±SE predation rates per predator were 6.2±0.8 individuals per 24h for dragonfly naiads and 5.1±0.7 for damselfly naiads. Predation rates were very low compared to previously recorded rates. However, unlike previous research, we did not focus on single species in a late stage of development but on multiple species in all stages that resembled the natural odonata community composition.

Control of fruit postharvest diseases: old issues and innovative approaches

Purpose of the review: This review focuses on the issues of fruit postharvest disease control; firstly the appearance of pathogen isolates resistant to common fungicides followed by stricter regulatory policies that impose a reduction in their use. Emphasis is given to the attempts to introduce effective biological control agents (BCAs) able to reduce fruit losses by an improvement in their formulation. Findings : At the beginning of the 1960s, treatments based on chemical fungicides as the main method of reducing postharvest fruit losses obtained satisfactory results. However, the fungicide option for managing postharvest decays is increasingly limited; in addition, the use of fungicides on fruit after harvest is regulated by different food protection agencies. The intense use of fungicides in the postharvest phase has contributed to the appearance of resistant isolates, widespread in packinghouses. Nowadays, fungicide resistance is frequently reported for the main fungal pathogens such as Penicillium , Monilinia , Botrytis, etc. Although the use of synthetic chemical fungicides remains a primary method of controlling postharvest diseases, the global trend appears to be shifting towards reduced use of fungicides, substituting them with alternative methods like biofungicides. However, the great effort made by researchers, documented by many peer-reviewed publications, has been only partially compensated by the appearance on the market of BCAs available for industrial application to control postharvest decays. Limitations : There are several reasons for the limited diffusion of biofungicides, some relate to an intrinsic ineffectiveness of BCAs such as their inconsistency, and the variability of the control under commercial conditions. Some are relate to their formulation which reduces the activity of antagonists with respect to the fresh cells, the high cost of the production, and the regulatory barriers to BCA registration in different countries that do not encourage their dissemination. Directions for further research : The formulation process represents an important step for maintaining a high and stable BCA efficacy. Dehydration of the product and maintenance in a dry environment is preferable to liquid formulations since antagonists can be handled using the normal distribution and storage channels. Unfortunately, not all microorganisms are able to survive drying conditions; they can lose viability during the drying process and storage. In order to avoid undesirable effects, cryoprotecting media have to be assessed during freeze-drying treatments in order to conserve antagonist viability. For example, in the case of Bacillus sp., its sporeforming ability could provide high resistance to extreme environmental conditions, making it a good candidate for developing stable and efficient products. In addition, the introduction of BCAs in wax or oil-based coatings can represent a useful strategy, above all for citrus fruit, papaya or mango that are treated by application of the coating after harvest.

Is there rapid evolutionary response in introduced populations of tansy ragwort, Jacobaea vulgaris, when exposed to biological control?

Differences in the herbivore community between a plant’s native (specialists and generalists) and introduced range (almost exclusively generalists) may lead to the evolution of reduced allocation to defences against specialist herbivores in the introduced range, allowing for increased allocation to competitive ability and to defences against generalist herbivores. Following this logic, the introduction of biological control agents should reverse this evolutionary shift and select for plants with life-history traits that are more similar to those of plants in the native range than those of plants in the introduced range that have not been exposed to biological control. In a common garden experiment, we compared performance and resistance traits of tansy ragwort, Jacobaea vulgaris, among populations from the introduced range (New Zealand and North America) that have either been exposed to or grown free from the biological control agent Longitarsus jacobaeae. For comparison, we included populations from the native European range. We found lower levels of generalist-deterrent pyrrolizidine alkaloids (PAs) and of soluble phenolics in New Zealand populations with than in populations without exposure to L. jacobaeae, while the opposite pattern was detected among North American populations. Contrary to expectation, populations with exposure to L. jacobaeae revealed more feeding damage by L. jacobaeae than populations without exposure. Introduced populations had higher levels of PAs and reproductive output than native J. vulgaris populations. Jacobaea vulgaris was introduced in different parts of the world some 100–130 years ago, while L. jacobaeae was introduced only some 20–40 years ago. Hence, the larger differences observed between native and introduced populations, as compared to introduced populations with and without biological control history, may result from different time scales available for selection to act.

How should the risk associated with the introduction of biological control agents be estimated?

1 Florida has an exceptional burden of invasive species. The history of the classical biological control of invasive arthropod pest species in the region largely is one of inadequate pre-release testing for nontarget effects. 2 A recent analysis indicated that a substantial risk of nontarget effects may exist in Florida, although the risk appears to be confined to a relatively small group of species within approximately ten families and documented cases of nontarget effects are rare, despite previous risky practices. 3 Great progress has been made recently in creating an organized framework for dealing with the uncertainty accompanying biological control importations in Florida and elsewhere. We suggest some ways in which balancing the risks and associated costs of releasing a biological control agent against the risks and associated costs of not releasing the agent may be improved. 4 Ultimately, experts will need to set some level of acceptable risk, and the ‘precautionary principle’ has been advanced to guide this process. As it stands, however, the precautionary principle applied to biological control falls short as a guide because it does not provide a prescription for action. 5 Florida case histories clearly illustrate both the complexity and urgency related to developing a prescription for action.