Examination of sex attractants for monitoring weed biological control agents in Hawaii

The identification of sex attractants was undertaken for potential use in the study of two biological control agents against Rubus spp. in Hawaii. Attractants for Croesia zimmermani (Lepidoptera: Tortricidae) and Schreckensteinia festaliella (Lepidoptera: Heliodinidae) were developed by field screening a variety of putative lures in sticky traps, based on attractants for congeneric species. Croesia zimmermani was most attracted to E11-tetradecen-1-ol and E11-tetradecenal, while S. festaliella was attracted to (10,12)-(E,E)-hexadecadienal alone. Development of monitoring systems based on sex attractants can enable better evaluation of biocontrol programmes, and provide cost-effective information on presence/absence, density, phenology, synchrony with the host, dispersal rate and other useful parameters.     

Opportunities for biological weed control in Europe

The development and application of biological weed control offer greatopportunities not only for farmers, nature conservationists and othervegetation managers but also for institutions and companies that wish tosell plant protection services and products, and for the general publicthat demands safe food and a visually attractive and diverseenvironment. Despite the obvious opportunities for biological weedcontrol, few control agents are actually being used in Europe. Potentialagent organisms have features that make them particularly strong anduseful for biological control, but they also have weaknesses. Weaknessesinclude a too narrow or too wide host specificity, lack of virulence, orsensitivity to unfavourable environmental conditions.Developing specific knowledge on the interaction between weeds andpotential biological control agents, as well as expertise to increasethe effect of control agents and so achieve sufficient weed control in acost-effective manner, should have the highest priority in researchprogrammes. From 1994 to 2000 most ongoing research on biological weedcontrol in Europe was combined in a cooperative programme. This COSTAction concentrated on the interactions between five target crop weedsand their antagonists (pathogens and insects), on furthercharacterisation of the specific blems and potential control agents andon the most suitable biological control approach.The next major challenge will be to apply the findings provided byCOST-816 to the development of practical control solutions. The leadingobjective of a new concerted research programme with European dimensionswill be to stabilise or even promote biodiversity in the most importantEuropean ecosystems by integrating biological weed control in themanagement of these systems.     

The value of simulating herbivory in selecting effective weed biological control agents

Invasive species have a significant economic and ecological cost and biological control can be a powerful tool in their management. Classical biological control practice involves the re-establishment of trophic links between specialist insect and fungal agents to regulate populations of invasive species. However, the permanent nature of biological control agent introductions raises concerns about the unintended consequences of such introductions on non-target organisms, particularly when such agents are ineffective on their target organisms. In this paper, we explore the current debate in the selection of agents for weed classical biological control. We then propose an alternate approach, based on studying plant response to simulated herbivory, that could minimize the chances of release of ineffective agents. Simulating herbivory could yield insights into the vulnerability of plants to certain types of damage. Selection of agents within guilds that are likely to have a significant influence on the plant can improve the chances of achieving biological control sooner and reduce the likelihood of releasing ineffective agents that may have non-target impacts. We propose a method by which simulated herbivory could be integrated into the agent selection process and discuss its strengths and shortcomings. We present case studies of two Neotropical weeds illustrating how this method could be applied.     

Selection of pathogen agents in weed biological control: critical issues and peculiarities in relation to arthropod agents

Abstract  Plant pathogens are playing an increasing role in classical biological control of weeds worldwide. This paper presents an explicit framework consisting of various interconnected steps to facilitate and streamline the selection process for pathogen agents. It also highlights and discusses critical issues associated with the various steps of the selection framework such as the climatic-matching approach to find well-adapted agents, host–pathogen matching and pathogen genetic structure. Processes and issues relating to the selection of pathogens are then contrasted with those usually adopted for arthropod selection in weed biological control. In both cases optimising the level of genetic diversity in introduced agents is seen as beneficial to biological control success. The difference in regulatory approach for multiple and genetically pure pathogen strains vs. genetically variable arthropod agents is highlighted for further scientific debate.     

Biocontrol without borders: the unintended spread of introduced weed biological control agents

An underlying assumption of classical biological control implies that intentionally introduced natural enemies will remain within the boundaries that delineate the program’s area of implementation. A weed biological control program targeting Melaleuca quinquenervia in Florida, USA has resulted in the release and establishment of Oxyops vitiosa and Boreioglycaspis melaleucae. An international survey of M. quinquenervia populations in 13 other states or countries where the insects have not been intentionally introduced was initiated to monitor the long range dispersal of O. vitiosa and B. melaleucae beyond the herbivores’ intended geographic range (Florida). Surveys in 2006 resulted in the discovery of B. melaleucae within the canopies of several M. quinquenervia trees near San Juan, Puerto Rico. In 2007, O. vitiosa was observed on the island of New Providence in the Bahamas but neither herbivore was detected on nearby Grand Bahama or Andros islands. In 2009, B. melaleucae was observed attacking M. quinquenervia trees in Los Angeles, California (USA). The herbivores have not been detected on other surveyed M. quinquenervia populations in Cuba, Jamaica, Texas (USA), Costa Rica, Brazil, Hawaii (USA) or South Africa. There is no evidence to suggest that herbivore colonization of New Providence, Puerto Rico, or California was influenced by linear distance between Florida and the recipient M. quinquenervia stand. While the dispersal pathway(s) remains unknown, biological control agents were detected from 200 to >3500 km from their original release location (Florida) and at locations that have strong links via tourism and trade as indicated by the number of airline flights connecting south Florida with colonized tree populations. Implications of this unintended spread are discussed in relation to permeability of biogeographical barriers and risk assessment of biological control agents.     

Risk analysis and management decisions for weed biological control agents: Ecological theory and modeling results

Biologically based control methods offer many advantages for the control of invasive plant species; however, these methods are not without risks to native species. Thus, there is a need for more effective and efficient methods of risk analysis for biological control agents. We show how the process of ecological risk assessment established by the United States’ Environmental Protection Agency may be adapted to improve assessment of the risks of proposed biological control agents. We discuss the risks posed by weed biological control agents, and present a simple individual-based model of herbivorous insect movement and oviposition on two species of host plant, a target invasive plant species and a non-target native species, in simulated landscapes. The model shows that risks of non-target impacts may be influenced by the details of the movement behavior of biological control agents in heterogeneous landscapes. The specific details of insect movement that appear to be relevant are readily measured in field trials and the general modeling approach is readily adapted to real landscapes. Current biological control risk assessments typically emphasize effects analysis at the expense of exposure analysis; the modeling approach presented here provides a simple and feasible way to incorporate exposure analyses. We conclude that models such as ours should be given serious consideration as part of a comprehensive strategy of risk assessment for proposed weed biological control agents.     

入侵种喜旱莲子草——主要天敌昆虫

喜旱莲子草是一种水陆两栖的重要入侵杂草,中国首批16种重要入侵物种之一.本文介绍了生物防治喜旱莲子草的天敌昆虫莲草直胸跳甲Agasicles hygophila、Vogtia malli、Amynothrips andersoni、阿根廷跳甲Disonycha argentinensis、Systena nitentula和虾钳菜披龟甲Cassida piperata等天敌的分类地位、形态特征、生物学、生态学特性以及国内外寄主专一性研究、释放效果与评价.     

Interactions between two biological control agents and their target weed: a beetle,a bug and a cactus weed

ABSTRACT

Pereskia aculeata Miller (Cactaceae) is an invasive alien shrub introduced into South Africa from Brazil. The leaf-feeding beetle, Phenrica guerini Bechyne (Chrysomelidae), was released as a biological control agent in South Africa in 1991 followed by the stem-wilting bug, Catorhintha schaffneri Brailovsky & Garcia (Coreidae), in 2014. This study investigated the interactions between the two agents under laboratory conditions. Potted plants were exposed to one of four treatments: control (no agents), P. guerini only, C. schaffneri only and both species together. Four densities, ranging from 2 to 12 insects per plant were used. Cathorhitha schaffneri alone at low to moderate densities resulted in the same reduction in number of leaves and shoot length as when combine with P. guerini. At the highest density, C. schaffneri reduced the number of leaves significantly more than any treatment. Mortality of P. guerini was significantly higher than C. schaffneri at the highest density when in combination. The antagonistic interaction between P. guerini and C. schaffneri suggests that these agents should not be released together because this would impact negatively on the overall biocontrol programme against P. aculeata. It is recommended that C. schaffneri should be released at sites where P. guerini is not present. Extrapolation of laboratory-based studies into the field is often challenging, so mass-rearing and releases of P. guerini should continue until there is convincing proof that C. schaffneri alone is more effective than P. guerini in the field.     

Scientific advances in the analysis of direct risks of weed biological control agents to nontarget plants

Research on host specificity testing protocols over the last 10 years has been considerable. Traditional experimental designs have been refined and interpretation of the results is benefiting from an improved understanding of agent behavior. The strengths, weaknesses, and best practice for the different test types are now quite clearly understood. Understanding the concept of fundamental host range (the genetically determined limits to preference and performance) and using this to maximize reliability in predicting field host specificity following release (behavioral expression of the fundamental host range under particular conditions) are still inconsistently understood or adopted despite having been identified as the critical steps in analyzing the threats posed by biological control agents to the agriculture and biodiversity of novel environments. This needs to be consistently understood and applied so the process of testing can follow a recognized process of risk analysis from hazard identification (identifying life stages of the agent that pose a threat and defining their fundamental host range) to uncertainty analysis based on the magnitude (predicted field host specificity following release) and likelihood of threats (predicted actual damage and impact) to nontargets. Modern molecular techniques are answering questions associated with subspecific variation in biological control agents with respect to host use and the chance of host shifts of agents following release. Guidelines for assessment of nontarget impacts need to recognize and adopt such recent developments and emphasize a general increased understanding of the evolution of host choice and the phylogenetic constraints to shifts in host use. This review covers all these recent advances for the first time in one document, highlighting how inconsistent interpretation by biological control practitioners can be avoided.     

Predictable risk to native plants in weed biological control

Data on field host use of 112 insects, 3 fungi, 1 mite, and 1 nematode established for biological control of weeds in Hawaii, the continental United States, and the Caribbean indicate that the risk to native flora can be judged reliably before introduction. Virtually all risk is borne by native plant species that are closely related to target weeds. Fifteen species of insects introduced for biological control use 41 native plant species; 36 of which are congeneric with target weeds, while 4 others belong to two closely allied genera. Only 1 of 117 established biological organisms uses a native plant unrelated to the target weed. Thus the elements of protection for the native flora are the selection of weed targets that have few or no native congeners and the introduction of biological control organisms with suitably narrow diets.     

A strategy for evaluating the safety of organisms for biological weed control

A strategy for establishing the specificity and safety of an organism as a biological weed control agent is described. A critical first step is to expose to its attack a small group of plants very closely related and exhibiting morphological and biochemical similarities to the weed. To prevent an erroneous negative result tests are also made on selected cultivated plants, including those closely related to the weed, those of which the associated insects and fungi are little known, those that have evolved apart from or been little exposed to the agent, those attacked by closely related organisms and those already recorded as hosts. The circumstances under which the strategy might fail to indicate safety are discussed, i.e. polyphagous organisms attacking plants irregularly distributed throughout many families, organisms highly specific to two alternate hosts, and those attacking two or three phylogenetically widely separated plant groups. The additional crop plant testing, included in the overall strategy to deal with such possible failures, is discussed. It is shown that the strategy would have included Sesamum tndicum in the list of plants challenged by the bug Teleonemia scrupulosa in biological testing for control of Lantana camara, thereby forewarning of the attack that was subsequently observed in Africa.     

Phytophagous insects and web-building spiders in relation to pasture vegetation complexity

We investigate the potential use of structural characteristics of vegetation as predictors of the densities of pasture arthropods in three Azorean islands. Two types of upland pastures, recent sown pastures (3–4 yr old) and wet semi-natural old pastures (> 35 yr old), were studied in three Azorean islands (S. Maria, Terceira and Pico), Three arthropod assemblages, of particular importance in pasture habitats, were assessed: insect forb-feeders, insect grass-feeders and web-building spiders. These are numerically abundant and represent a range of feeding strategies. Point quadrats for plants and suction (Vortis) for arthropods were used as sampling methods. Several vegetation indices were investigated, but only three (cover abundance of perennial forbs, cover abundance of perennial grasses and the total vegetation alpha-diversity) were good predictors of invertebrate abundance. Vegetation structure, defined by a Height Index, was of minor predictive value. In sown and semi-natural pastureland, diverse and structurally complex pasture sites support more individual insect forb-feeders. grass-feeders and web-building spiders per unit area than less complex ones.     

Indirect nontarget effects of host-specific biological control agents: Implications for biological control

Classical biological control of weeds currently operates under the assumption that biological control agents are safe (i.e., low risk) if they do not directly attack nontarget species. However, recent studies indicate that even highly host-specific biological control agents can impact nontarget species through indirect effects. This finding has profound implications for biological control. To better understand the causes of these interactions and their implications, we evaluate recent case studies of indirect nontarget effects of biological control agents in the context of theoretical work in community ecology. We find that although particular indirect nontarget effects are extremely difficult to predict, all indirect nontarget effects of host specific biological control agents derive from the nature and strength of the interaction between the biological control agent and the pest. Additionally, recent theoretical work suggests that the degree of impact of a biological control agent on nontarget species is proportional to the agent’s abundance, which will be highest for moderately successful control agents. Therefore, the key to safeguarding against indirect nontarget effects of host-specific biological control agents is to ensure the biological control agents are not only host specific, but also efficacious. Biological control agents that greatly reduce their target species while remaining host-specific will reduce their own populations through density-dependent feedbacks that minimize risks to nontarget species.     

Use of CLIMEX modelling to identify prospective areas for exploration to find new biological control agents for prickly acacia

Abstract  Selection of biocontrol agents that are adapted to the climates in areas of intended release demands a thorough analysis of the climates of the source and release sites. We present a case study that demonstrates how use of the CLIMEX software can improve decision making in relation to the identification of prospective areas for exploration for agents to control the woody weed, prickly acacia Acacia nilotica ssp. indica in the arid areas of north Queensland.