Management of ectoparasites with biological control organisms

Biological control is not a new concept, but for many reasons it is gaining interest for control of livestock ectoparasites. These reasons will be discussed, both from a political view and from environmental and economic views. The US government has vowed to reduce pesticide use by the year 2000, but other forces may drive this change even faster. Pesticide costs are high, and efficacy against some pests is questionable. Also, many producers are concerned about the environment, and are anxious to do their part to reduce chemical pollution. Specialised training is required to reduce on-the-farm difficulties involved with the use of biological-control organisms. Otherwise, how do producers or veterinarians purchase and use biocontrol organisms, and how do they critique what has been purchased? Included is a short summary of the three most common ectoparasites of livestock, and the type of biological-control strategies being developed to combat them. Much of the classical work has been done on filth fly control, most likely because of the nuisance status of flies, and because of the availability of candidate beneficial organisms, particularly parasitic wasps. And finally, two fly-control success stories will be briefly described. Tremendous strides have been made in house-fly and stable-fly control with parasitic wasps on feedlots, but more work is needed to better understand the habits of immature fly populations. A predaceous fly is being tested for pest fly control in dairies. Larvae of this fly can kill 15-20 house-fly larvae daily, and the adults do not become pestiferous on farms or around homes. Biological control will be an important part of livestock pest control in the future, but its implementation will require a corps of educated producers who are confident that biological control can work for them.     

Improving biological control

Nature Wars: People vs. Pests by Mark L. Winston Harvard University Press, 1997. ￡16.50/$24.95 hbk (x +210 pages) ISBN 0 674 60541 1.     

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.     

Impulsive control strategies in biological control of pesticide

By presenting and analyzing the pest-predator model under insecticides used impulsively, two impulsive strategies in biological control are put forward. The first strategy: the pulse period is fixed, but the proportional constant E(1) changes, which represents the fraction of pests killed by applying insecticide. For this scheme, two thresholds, E(1)(**) and E(1)(*) for E(1) are obtained. If E(1)>or=E(1)(*), both the pest and predator (natural enemies) populations go to extinction. If E(1)(**)相似文献   

生境管理——保护性生物防治的发展方向

生境管理是近年来保护性生物防治的重要研究方向,也是利用农业景观格局进行生物防治的重要策略。生境管理是指从农田景观的角度,在大时空尺度范围内进行多种作物与非作物生境的设计与布局,创造有利于天敌的环境条件,抑制害虫种群发生,达到减小环境污染、增强农业生态系统的控害保益功能,最终实现害虫种群控制的可持续性。景观尺度下的生境管理不仅强调单一农田生物控害作用,而是以多生境农业景观整体布局为指导,探索各种生境功能的整合利用,以发挥各种生境最大的生物控害潜能,为实现多目标生态服务价值管理提供重要的理论基础和现实依据。本文系统地总结了生境管理的研究内容与实现途径,论述了农业景观格局与过程对害虫种群控制的机理,并对作为保护性生物防治发展方向的生境管理研究趋势进行了展望。     

Approaches to biological control problems

There has recently been some discussion as to the most effective methods of carrying out biological control investigations — the need for detailed ecological investigations, life-table studies, population studies, etc. This paper presents conclusions in this regard based on over 30 years experience in this field in many parts of the world. Often practical considerations make it impossible to carry out the long-term detailed ecological studies which would give a very valuable and scientifically interesting background to any biological control attempt before any introductions of beneficial species were made. Suggestions are made for the continuation of both short-and long-term procedures to be adopted in biological control work and examples cited of the value of both approaches.

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Résumé Quelques discussions ont eu lieu récemment concernant les méthodes les plus efficaces à appliquer dans les recherches sur la lutte biologique: nécessité d’investigations écologiques approfondies, études de tables de mortalité, études de populations, etc. Le présent article propose à ce sujet des conclusions fondées sur plus de 30 ans d’expérience dans de nombreuses parties du monde. Souvent, des considérations pratiques rendent impossibles les études écologiques à long terme, susceptibles d’apporter dans toute tentative d’application de lutte biologique, une connaissance de base scientifiquement très intéressante et très utile, préalablement à l’introduction d’organismes utiles. L’auteur suggère l’adoption simultanée, dans les travaux de lutte biologique, à la fois de la méthode à court terme et de la méthode à long terme; il cite des exemples de la valeur de ces deux stratégies.

     

A knapweed biological control perspective

Diffuse and spotted knapweed (Centaurea diffusa Lam. and C. stoebe micranthos (Gugler) Hayek) are Eurasian plants that devastate dry and mesic North American grasslands. They have a mutualistic association with arbuscular mycorrhizal fungal (AMF) phylotypes with hyphal links to nearby plants and a nutrient flux to the strongest sink, usually knapweed. They displace many AMF beneficial to grass and affect knapweed nutrient allocation, biology, knapweed insects and probably root necrosis and emergence of ant buried seed. AMF determined nutrient root or shoot allocation determines nutrient shoot and root allocation and the benefit to root or seed-head insect species and whether C. diffusa is an annual–biannual or a semelparous perennial needing 5 or more years to flower. Both knapweeds do well without its AMF phylotypes without competition in fertile soil. In grass in Eurasia, they have a community of seven seed-head species segregated by head development stage. Prolonged seed dormancy buffered knapweed decline that resulted in release of a surfeit seed-head species. The presence of an eliasome on the seed and vigorous seedling clumps suggests burial by myrmecochorous ants with AMF supplied carbon supporting their growth. The root species community is segregated by habitat, climate, root part, and size. With larval induced compensatory growth and AMF nutrient sharing, the growth of plants with and without a larva was the same. On feeding completion, a nutrient out flux from the attacked plants reduced growth; but without killing. This needs a dual species or a repeated single species attack. Root species packing increases knapweed utilization; but the four approved species are insufficient for maximum utilization. Two additions are suggested. The aim of the paper is to provide enough understanding of the AMF and its plant and insect interactions to facilitate knapweed biological control and avoid past mistakes.     

Some recent puzzles in biological control

Six recent examples of biological control successes are described with comments on how these have been achieved. They are that ofPromecotheca cumingi Baly in Sri Lanka,Diatraea saccharalis (F.) in Barbados,Mythimna separata (Wlk.) in New Zealand,Nezara viridula (L.) in Australia,Chilo partellus (Swinh.) in Pakistan andEupatorium odoratum L. in Sri Lanka (as compared with other areas). Each shows some peculiar features which may well be of interest when considering future biological control attempts. In general it is postulated that since the introduction of the beneficial species into a new area is the final test of its capabilities this should not be delayed in order to find out more about its detailed ecology, which may actually be irrelevant. Once it is shown that an introduction cannot be harmful it should be attempted, in order to obtain possible economic results as quickly as possible.

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Résumé L'auteur décrit six récents exemples de succès en matière de lutte biologique et ajoute des commentaires sur leur réalisation. Il s'agit de la lutte contrePromecotheca cumingi Baly au Sri Lanka,Diatraea saccharalis F. aux Barbades,Mythimna separata Walk. en Nouvelle Zélande,Nezara viridula L. en Australie,Chilo partellus Swinh. au Pakistan etEupatorium odoratum L. au Sri Lanka (en comparaison avec d'autres régions). Chaque cas montre quelques particularités qui pourraient bien être instructives lors de futurs essais de lutte biologique. En général, l'auteur postule que l'introduction des espèces utiles dans une nouvelle région peut seule apporter la preuve définitive de leur capacité d'action et que cette introduction ne doit pas être retardée sous le prétexte de recherches sur leur écologie détaillée, ce qui peut en réalité être une faute. Dès qu'il est prouvé qu'une introduction ne peut pas être nuisible, elle doit être tentée de manière à obtenir des résultats d'ordre économique le plus vite possible.

     

利用植绥螨防治烟粉虱的研究进展

对目前利用植绥螨防治烟粉虱Bemisia tabaci(Gennadius)的研究现状进行综述。主要介绍植绥螨作为生防作用物的应用历史、替代食物在利用植绥螨进行生物防治中的作用,并对代表种Typhlodromips(Amblyseius)swirskiiAthias-Henriot等作为烟粉虱生防作用物的最新研究进展、产业化现状、应用前景及可能存在的问题进行了分析,以期为这些植绥螨的引进和利用提供参考。     

Modeling biological motor control for human locomotion with functional electrical stimulation

This paper develops a novel control system for functional electrical stimulation (FES) locomotion, which aims to generate normal locomotion for paraplegics via FES. It explores the possibility of applying ideas from biology to engineering. The neural control mechanism of the biological motor system, the central pattern generator, has been adopted in the control system design. Some artificial control techniques such as neural network control, fuzzy logic, control and impedance control are incorporated to refine the control performance. Several types of sensory feedback are integrated to endow this control system with an adaptive ability. A musculoskeletal model with 7 segments and 18 muscles is constructed for the simulation study. Satisfactory simulation results are achieved under this FES control system, which indicates a promising technique for the potential application of FES locomotion in future.     

Risk and ethics in biological control

All introduced natural enemies present a degree of risk to nontarget species. Since most biological control programs use relatively host-specific natural enemies, the risk to nontarget species is generally very low, particularly from biological control of weeds, which uses extensively tested and validated host-specificity testing procedures to predict risk. However, many of the published comments about risks of biological control are superficial or misleading, often inappropriately lumping risk from all taxa of agents as “the risk of biological control,” and ignore the potential benefits, rather than dealing with species-by-species risk and benefits. Particularly confounding accurate predictions is the common mixing of parameters of hazard and exposure in discussions of risk. In this paper, traditional risk analysis techniques are discussed and adapted for biological control. How people perceive risk is the key to understanding their attitude to risk. Some of the criticisms of biological control relating to inadequate post-release monitoring are valid and the ethical responsibilities of biological control scientists in this area are also discussed. Biological control scientists should address objectively the criticisms of biological control, continue to review and adjust current host-specificity testing procedures and make appropriate changes. This process will result in better science, ultimately delivering more focused programs, and altering the perception of risk from biological control agents by objective observers.     

Conservation biological control using fungal entomopathogens

Conservation biological control relies on modification of the environment or management practices to protect and encourage natural enemies that are already present within the system, thereby enhancing and improving their ability to control pest populations in a reliable way. Such strategies are only possible when based on a strong understanding of the ecology of the species concerned at the individual, community and landscape scale. Conservation biological control with entomopathogenic fungi includes the manipulation of both the crop environment and also habitats outside the crop. Further investment in conservation biological control with entomopathogenic fungi could make a substantial contribution to sustainable crop production either as stand alone strategies or, more importantly, in support of other biological and integrated pest management strategies.