Similarly, advances in disciplines such as invasion biology and molecular genetics provide insight into factors affecting natural enemy establishment e. Perhaps the most significant recent advancement has been in understanding the interactive effects the microbiome of the target pest and the natural enemy have and how microbial level interactions affect host resistance and natural enemy efficacy e. Many of these tools need to be used simultaneously when developing a biological control program though perhaps the most underrated tool is simply perseverance during the establishment phase of initial natural enemy releases.
Citricola scale, Coccus pseudomagnoliarum Kuwana Hemiptera: Coccidae , is an exotic pest of citrus in California. Infestations on citrus were first detected in California around , but it is likely that the scale invaded earlier than this [ ]. The major economic damage caused to citrus by citricola scale is due to heavy infestations on branches that can cause die back and reduction in flowering and fruit set i. It was originally concluded that citricola scale, initially confused with brown soft scale, Coccus hesperidum L. Coccidae , was invasive, but its area of origin was unknown at time of first detection [ ].
In addition to infesting citrus, its preferred host species in California, citricola scale was also recorded from pomegranates Punica granatum L. Several striking biological differences eventually led citrus researchers to conclude that citricola scale was not a biotype of brown soft scale. First, in California, citricola scale is univoltine and brown soft scale is multivoltine. Second, the invasive Argentine ant, L. Third, citricola scale produce offspring via eggs, while brown soft scale females give birth to live crawlers.
Fourth, citricola preferentially infests older woody material, while brown soft scale is found more commonly on younger plant growth. Fifth, very few parasitoids are associated with citricola scale and biological control is typically poor in some areas, especially in the SJV. In comparison, the parasitoid fauna on C. Sixth, several misidentifications were made of citricola scale i. Misidentifications of a new invasive pest are not uncommon, especially if the species is undescribed, access to type specimens is difficult, and keys to described species are being used in an attempt to identify a newly established insect that is new to science.
These observed biological differences, coupled with morphological differences, led to the description of a new species, C. Quayle [ ] presciently pointed out that this new species, C. This happened and C. Curiously, Clausen [ ] notes that morphological differences between L. Quayle [ ] speculated that hackberry imported from Japan might have been the source of the invasive population in California. Significant foreign exploration efforts were made in Japan for natural enemies of citricola scale that could be used in a classical biocontrol project targeting this pest in California [ ].
Attempts to introduce and establish at least six species of citricola parasitoid over , , , , and failed, and in some instances, parasitoids could not be maintained in quarantine on colonies of California citricola scale [ ]. Field surveys in Japan indicated that the parasitoid fauna associated with citricola scale could vary markedly depending on the species of host plant on which the scale was infesting [ ]. Several hypotheses have been postulated as to why classical biological control of citricola scale in the SJV failed. The need for effective biological control of citricola scale in the SJV is increasing because broad-spectrum pesticides, organophosphates and carbamates, targeting other citrus pests e.
Diaspididae] have historically controlled citricola scale. These compounds are being replaced with new generation pesticides that may not be as effective as the compounds they are replacing [ ]. Further, pesticide resistance has been detected in populations of citricola scale in the SJV weakening the efficacy of available products [ ]. Increasing restrictions on the use of pesticides and resistance development has allowed citricola scale to re-emerge as a significant pest of citrus [ ]. These attributes would promote parasitoid survival even though the scale is univoltine and only one size of life stage is present at any given time; 2 Parasitoids should be sourced from areas with a good climate match with the SJV, as hot summer temperatures could have a strong negative impact on the survivorship of species with poor climatic adaptations [ ]; 3 Generalist scale parasitoids could be advantageous as they could use other pest scales as hosts should susceptible stages of citricola scale be unavailable at certain times of the year.
This latter suggestion would need very careful scrutiny and consideration given the significant movement towards high host specificity for natural enemies of arthropod pests [ 5 ]. The Universal Chalcidoidea Database http: Given this potentially rich species complex, the ideal citricola parasitoid according to Kennett et al. In comparison to the SJV, citricola scale is under good biological control in southern California and is not as problematic because parasitoids attacking black scale, Saissetia oleae Olivier Hemiptera: Coccidae , which is a multivotine pest, spill off this host and exploit susceptible stages of citricola scale when they are present [ ].
This does not happen in the SJV, as citricola scale immatures are too small when parasitoids attacking black scale are most active [ ]. Biological control of citricola scale may now be emerging as an important control option again because of emerging issues with conventional control strategies that are reliant on pesticides. One step in this direction has been to use augmentative releases of black scale parasitoids for citricola scale control [ , ].
However, there are significant biological [ ] and economic limitations to this approach because of the large numbers of parasitoids needed for release per acre. The use of banker plants, Yucca sp. Interestingly, this approach would require active encouragement of ants to tend brown soft scale colonies to prevent parasitoids from completely eliminating infestations on Yucca sp. Morse, but it has not been field tested. Citricola scale is an excellent example of a legacy pest, and classical biological control of this important citrus pest in California should be revisited using modern tools.
Suggested steps in developing a new biocontrol program targeting citricola scale with new tools are provided below. The failure of establishment of citricola scale parasitoids from parts of the presumed native range may be indicative of the incorrect identification of the target pest in Japan.
It is possible that past collection efforts were made from a scale species that was not the same species as that in California, a possibility hinted at by Clausen [ ]. Accurate species identification for this project is imperative as all available published foreign exploration records indicate that natural enemy collections have only been made in Japan and any uncertainty over species identifications could be readily resolved via molecular work. Additionally, the native range of citricola scale is not well understood and needs to be better refined.
The general area of origin is thought to include parts of China, Taiwan, Korea, and Japan, and citricola scale sensu latu in this vast area may be comprised of multiple species that are difficult to separate morphologically and are all considered to be C. The possibility of microbes protecting California populations of citricola scale from parasitoids should be investigated to determine if defensive endosymbionts are present and if they have the potential to affect the efficacy of different natural enemy species attacking citricola scale.
If defensive endosymbionts are detected in citricola scale in California, these organisms may have contributed, in part, to past establishment failures of imported parasitoids from Japan. Collection efforts would therefore need to target natural enemies that are co-adapted to specific protective endosymbiont strains found in California citricola scale populations.
Climate matching tools should be used to guide foreign exploration efforts for natural enemies of citricola scale in the native range, and ecological niche modeling could assess potential climate influences on the suitability of the SJV for natural enemy persistence when sourced from different areas within the presumed home range of citricola scale.
The most host specific natural enemies of citricola scale need to be identified. This could be done either by studying the pest-natural enemy complex in their home range and importing potential best candidates into quarantine for host specificity testing, or by returning to quarantine candidate species for testing without a priori knowledge of their specificity. Polyphagous species should be excluded from consideration as biocontrol agents, and efforts should focus on species with high host specificity because they may have the greatest potential for establishing and controlling the target.
In quarantine, the genetic diversity of collected natural enemies needs to be maintained and the use of isolines or isofamilies could be very important for preserving genetic variation. One way to do this would be to maintain separate natural enemy rearing cages with each cage representing a unique combination of collection location and time. Genetic variation preserved in cages holding isolines or isofamilies would be reconstituted by removing individuals from these cages and introducing them into hybridization cages to facilitate panmictic mating.
Resulting hybrid offspring with presumably increased levels of genetic diversity would be released. The number individuals released and frequency of releases will play an important role in establishment success. For example, releases should be made when host phenology is correct for natural enemy reproduction, hosts are abundant, and floral resources or some other food subsidy is available for newly released natural enemies and their anticipated offspring.
Site security needs to be ensured to minimize preventable accidents such as pesticide sprays or pruning of trees which could accidentally eradicate incipient natural enemy populations. Classical biological control of arthropod pests infesting perennial crops is an important pest management tool and often a key component of integrated pest management programs.
However, there are some significant pests of tree crops grown in California that established prior to or have been present for more than 25 years that have not been successfully suppressed by natural enemies even though they were targets of biocontrol projects. We acknowledge that numerous reasons may exist for the failure of these programs. However, we contend that certain legacy pests may be good targets for classical biological control even if past efforts were unsuccessful. The development of new tools as discussed here could now provide opportunities to revisit old pest problems, and their application may increase the chances of successfully developing biocontrol programs.
Citricola scale in California is an example of a legacy pest of citrus, which has been subjected to multiple biocontrol projects that have failed. Application of new tools, such as DNA-based analyses to determine species identities and areas of origin, climate matching, ecological niche modeling, and microbiome analyses, which were previously unavailable to scientists undertaking citricola scale biocontrol, have the potential to significantly influence the success of future projects targeting not only this pest but other legacy pest species as well.
National Center for Biotechnology Information , U. Journal List Insects v. Published online Dec Author information Article notes Copyright and License information Disclaimer. Received Nov 11; Accepted Dec This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license http: This article has been cited by other articles in PMC. Introduction Invasive species pose major ecological and economic threats to agriculture worldwide [ 1 ]. Molecular Tools for Identifying Pest and Natural Enemy Species DNA-based tools are now indispensable technologies in the development of modern classical biological control programs.
Climate Matching Tools Selecting areas for foreign exploration for natural enemies needs to take into consideration similarities between the climate of the source area for the biocontrol agents and the receiving area for their release. Modeling Tools The number of natural enemy species to release against a target pest to maximize the likelihood of successful control is a controversial issue [ 50 ]. Tools to Preserve Genetic Variation in Natural Enemies Collected from Foreign Exploration All classical biocontrol programs import natural enemies for release into a new range where they have not existed previously.
Tools for Evaluating the Host Range and Host Specificity of Natural Enemies A recent and significant development in arthropod biological control has been the development and utilization of host range tests for entomophagous natural enemies i. Propagule Pressure and Establishment Likelihood A significant determinant underlying successful natural enemy introductions that have gone through genetic bottlenecking processes is the number of individuals released. Providing Resources to Natural Enemies An emerging area that is receiving increasing attention is conservation biological control, the deliberate act of providing shelter and food resources e.
Disruptive Mutualisms and Biotic Resistance Another impediment to successful biological control can be invader-invader interactions that disadvantage the natural enemy. Pest and Natural Enemy Coevolution Pest and natural enemy coevolution are post-release processes that could affect long-term stability and efficacy of a classical biological control project [ ]. Using New Tools in the Toolbox Past analyses of unsuccessful biological control projects have focused on identifying potential causes such as establishment failure [ 31 , 80 ], lack of adequate control if natural enemies established [ 6 , ], and biological, ecological, and behavioral traits that theoretically define a successful natural enemy [ ].
Application of Molecular Tools to Determine Species Identities, Area of Origin, and Identity of Defensive Endosymbionts The failure of establishment of citricola scale parasitoids from parts of the presumed native range may be indicative of the incorrect identification of the target pest in Japan. Climate Matching and Ecological Niche Modeling Climate matching tools should be used to guide foreign exploration efforts for natural enemies of citricola scale in the native range, and ecological niche modeling could assess potential climate influences on the suitability of the SJV for natural enemy persistence when sourced from different areas within the presumed home range of citricola scale.
Conclusions Classical biological control of arthropod pests infesting perennial crops is an important pest management tool and often a key component of integrated pest management programs. Author Contributions All authors contributed equally to this paper. Conflicts of Interest The authors declare no conflict of interest. Ecology, Economics, Management, and Policy.
Biological Control of Insect Pests and Weeds. Methods and Risk Assessment. Behavioral studies, molecular approaches, and modeling: Methodological contributions to biological control success.
Progress in risk assessment for classical biological control. A history of methodological, theoretical, and empirical approaches to biological control. Nuclear-mitochondrial barcoding exposes the global pest western flower thrips Thysanoptera: Thripidae as two sympatric cryptic species in its native California. The lesser of two weevils: Molecular-Genetics of pest palm weevil populations confirm Rhynchophorus vulneratus Panzer as a valid species distinct from R.
Evolutionarily significant units in natural enemies: Identifying regional populations of Aphidius transcaspicus Hymenoptera: Braconidae for use in biological control of mealy plum aphid. Reevaluating establishment and potential hybridization of different biotypes of the biological control agent Longitarsus jacobaeae using molecular tools. Systematics in relation to biological control. Taxonomy and biological control.
Handbook of Biological Control. Successful biological control of the floating weed salvinia. Tumbleweed Salsola section Kali species and speciation in California. A review of research into its identity and biological control in South Africa. Integrating DNA data and traditional taxonomy to streamline biodiversity assessment: Will DNA barcoding advance efforts to conserve biodiversity more efficiently than traditional taxonomic methods? Biological identifications through DNA barcodes.
The promise of DNA barcoding for taxonomy. DNA barcoding a useful tool for taxonomists. DNA barcoding does not compete with taxonomy. Relationships among species of Scirtothrips Thysanoptera: Thripidae using molecular and morphological data. More taxonomy, not DNA barcoding. DNA barcoding is no substitute for taxonomy. Foreign exploration for beneficial organisms.
Evolution and ecology of species range limits. Climate, climate change, and range boundaries. Climate and the effectiveness of Psyllaephagus bliteus as a parasitoid of the red gum lerp psyllid. Why do natural enemies fail in classical biological control programs? Biological control attempts by introductions against pest insects in the field in Canada.
Success in biological control of terrestrial weeds by arthropods. Control of Pests and Weeds by Natural Enemies: An Introduction to Biological Control. Predicting the limits of the potential distribution of alien crop pests. Invasive Arthropods in Agriculture—Problems and Solutions. Predicting the potential invasive range of light brown apple moth Epiphyas postvittana using biologically informed and correlative species distribution models.
Prediction of species geographic ranges. Host range testing of Tamarixia radiata Hymenoptera: Eulophidae sourced from the Punjab of Pakistan for classical biological control of Diaphorina citri Hemiptera: Selecting arthropod biological control agents against arthropod pests: Can the science be improved to decrease the risk of releasing ineffective agents?
Modeling of species distributions with Maxent: New extensions and a comprehensive evaluation. Climate matching techniques to narrow the search for biological control agents. Use of CLIMEX modelling to identify prospective areas for exploration to find new biological control agents for prickly acacia. Predicting insect distributions from climate and habitat data. Comparison of the thermal performance between a population of the olive fruit fly and its co-adapted parasitoids.
Use of life table statistics and degree-day values to predict the invasion success of Gonatocerus ashmeadi Hymenoptera: Mymaridae , an egg parasitoid of Homalodisca coagulata Hemiptera: Cicadellidae , in California. Predictions of invasion success of Gonatocerus triguttatus Hymenoptera: Mymaridae , an egg parasitoid of Homalodisca vitripennis Hemiptera: Cicadellidae , in California using life table statistics and degree-day values. Adaptive evolution of an insect introduced for biological control. Targeting biological control across diverse landscapes: The release, establishment, and early success of two insects on mesquite Prosopis spp.
How many insect species are necessary for the biological control of insects? Multiple agents in biological control: Effects of multiple natural enemy species on plant performance. Modelling the effect of two biocontrol agents on the invasive alien tree Acacia cyclops —Flowering, seed production, and agent survival. Evaluating management strategies and recovery of an invasive grass Agropyron cristatum using matrix population models.
Prospective modelling in biological control: An analysis of the dynamics of heteronomous hyperparasitism in a cotton-whitefly-parasitoid system. The usefulness of destructive host feeding parasitoids in biological control: Theory and observation conflict. Dynamical effects of host feeding in parasitoids. Competition among parasitoid species on a stage structured host and its effect on host suppression.
Life history characteristics of Aphidius transcaspicus , a parasitoid of mealy aphids Hyalopterus species. Predictive modeling in biological control: The mango mealy bug Rastrococcus invadens and its parasitoids. Theories and mechanisms of natural population regulation. Modelling the biological control of insect pests: A review of host-parasitoid models. Biological control and precipitation effects on spotted knapweed Centuarea stoebe: Empirical and modeling results.
Nonlinearities lead to qualitative differences in population dynamics of predator-prey systems. Management of genetics of biological-control introductions. Use of single family lines to preserve genetic variation in laboratory colonies. Rapid genetic deterioration in captive populations: Causes and conservation implications.
Classical biological control of Asian citrus psyllid with Tamarixia radiata in urban Southern California. Genes in new environments: Genetics and evolution in biological control. Effects of a biological control introduction on three nontarget native species of saturniid moths. Benefits and harm caused by the introduced generalist tachinid, Compsilura concinnata , in North America.
Selection of non-target species for host specificity tests. Biological Control of Arthropods using Invertebrates: Methods for Environmental Risk Assessment. Using exotic species to control invasive exotic species. Biological control in support of conservation: Experimental Approaches to Conservation Biology.
Predicting successes and risks of intentional introductions for arthropod biological control.
Handbook of biological control : principles and applications of biological control
Higher establishment success in specialized parasitoids: Support for the existence of trade-offs in the evolution of specialization. Post release evaluation of Rodolia cardinalis Coleoptera: Coccinellidae for control of Icerya purchasi Hemiptera: Monophlebidae in the Galapagos Islands. The biology of small introduced populations, with special reference to biological control. The population genetics of a biological control introduction: Mitochondrial DNA and microsatellite variation in native and introduced populations of Aphidius ervi , a parasitoid wasp.
Avoidable obstacles to colonization in classical biological control of insects. Optimal release strategies for biological control agents: An application of stochastic dynamic programming to population management. Role of propagule pressure in colonization success: Disentangling the relative importance of demographic, genetic, and habitat effects. Mate finding, dispersal, number released, and the success of biological control introductions. Experimental invasions using biological control introductions: The influence of release size on the chance of population establishment.
BIREA: Biological control
The effect of release size on the probability of establishment of biological control agents: Gorse thrips Sericothrips staphylinus released against gorse Ulex europaeus in New Zealand. Ecological engineering, habitat manipulation, and pest management. Plant-Provided Food for Carnivorous Insects: A Protective Mutualism and Its Applications. A Protective Mutualism and its Applications. Does floral nectar improve biological control of parasitoids? Improved fitness of aphid parasitoids receiving resource subsidies. Selecting effective parasitoids for biological control introductions: Codling moth as a case study.
The influence of host deprivation and egg expenditure on the rate of dispersal of a parasitoid following field release. Evaluation of floral resources for enhancement of fitness of Gonatocerus ashmeadi , an egg parasitoid of the glassy-winged sharpshooter, Homalodisca vitripennis. The effect of resource provisioning and sugar composition of foods on longevity of three Gonatocerus spp. Difficulties Encountered in the Measurement of Biocontrol. Resource Allocation For Research. Size of Research Effort. The phenomenal development and increased use of organic pesticides in agriculture after has been a mixed blessing and has led to heated contemporary debates.
An attitude of unreserved optimism became prevalent among most entomologists with demonstrations of the spectacular effectiveness of DDT. Failures of synthetic organic insecticides to control all pests have changed this attitude to a more rational but somewhat pessimistic one. Development of insecticide resistant populations, resurgence of treated pest populations, evaluation of secondary pests or in some cases previously innocuous species to a status of primary importance, deleterious effects on populations of nontarget organisms, and general pollution of the environment with measurable residues of persistent chemicals have posed increasingly critical problems.
It is not surprising, then, that considerable interest has been shown in recent years in Integrated Pest Management IPM. The term " Integrated Control " apparently was first proposed by Dr. Blair Bartlett, University of California, Riverside in , although the first actual demonstration of the technique was by the Swiss entomologist, F. Schneider in Sumatra in the 's and working on gambir plantations. Bartlett used the term to designate applied pest control that combines and integrates biological and chemical measures into a single unified pest control program.
Chemical control is used only where and when necessary, and in a manner that is least disruptive to beneficial regulating factors of the environment, particularly naturally occurring arthropod parasitoids, predators and pathogens. In the early 's the first suggestions arose for broadening the concept to include the integration, not only of chemical and biological control method, but of all practices, procedures and techniques relating to crop production, into a single unified program aimed at holding pests at subeconomic levels.
Thus, the concept evolved from a two-component system chemical and biological control to the much broader concept of pest management. All the proposed definitions have one common theme: Terms frequently used in discussions of integrated pest management: Each species of arthropod pest occurring in our various agricultural ecosystems falls into one of three categories: Usually one or two key pest species are common to each agricultural ecosystem, these being those serious, perennially troublesome species that dominate control practices.
Occasional pests , in contrast to key pests, are those arthropods that only cause economic damage in certain places in certain years. Such pest are usually under adequate biological or natural control which is disrupted occasionally or fails for various reasons. Potential pests are those species which normally cause no economic damage, but as a result of chemicals or cultural practices are allowed to realize their potential for damage.
Basic to the concept of integrated pest management is the notion that most potential pests have effective natural enemies. Also basic is the concept that the ability of natural enemies to effect only partial control of a pest should not invoke chemical control practices that disrupt either this partial control or the controlling action of natural enemies of other potential pests in the agricultural ecosystem. Pest - Upset versus Pest Resurgence. Sole reliance on chemicals for pest control has the following drawbacks: Selection of resistance to insecticides in pest populations.
Cross resistance also is hastened. Resurgence of treated populations. Outbreaks of secondary pests. Residues, hazards and legal complications.
Destruction of beneficial species, including parasitoids, predators and pollinating insects. Expense of pesticides, involving recurring costs for equipment, labor and material. Two types of selectivity: Factors that can determine physical selectivity.
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Preservation of natural enemy reservoirs during treatment, either within treated areas or within easy migrational distances from them. Timing pesticide treatments to allow for the differential susceptibility and seasonal occurrence of the various developmental stages of natural enemies. Physical selectivity may also be conferred by the feeding habits of various natural enemies. Physical selectivity also can be conferred by manipulating the dosage and persistence of pesticides. Physiological selectivity is conferred by a pesticide that is more toxic to a pest species than to its natural enemies.
But, unfortunately, the reverse is usually true. A few pesticides have been developed that are fairly specific against certain groups or species of arthropods. Physiological selectivity is a costly achievement. The costs involved in the research and development of pesticides are tremendous, well in the range of million dollars per compound. If more of the highly specific pesticides are to be developed for integrated control, something probably will have to be done to offset those tremendous developmental costs to industry, for obviously the marketing potentials of selective and specific pesticides are much less than those of broad-spectrum compounds.
To make matters worse for industry, successful integrated control programs have resulted in smaller demands for pesticides and a reduced demand for broad-spectrum compounds. The continuation of this trend could deter industry from trying to find additional specific compounds with limited market potentials. Pest Management Conflicts See Discussion. Ecologically Selective Ways of Using Pesticides.
Because populations of natural enemy species collected from different locations may differ in their susceptibility to a pesticide Rosenheim and Hoy ; Rathman et al. Also, information about effects of one pesticide is often not useful in predicting the toxicity of other pesticides to a given natural enemy or to other natural enemies Bellows and Morse These facts dictate that only comprehensive local testing of pesticide-major natural enemy combinations can fully define which materials may be safely used in a crop for spiders and brown planthopper on rice in the Philippines, see Thang et al.
Test methods are sensitive to the precise conditions selected for the assay. Careful attention is given to standardizing the source, age, sex, and rearing history of the natural enemies used in tests, as well as the temperature, relative humidity, and degree of ventilation of the test environment, and the formulation, purity, and dosage of the test material Croft The use of standardized assay conditions, such as those developed by the IOBC International Organization for Biological Control is critical if studies are to be compared Hassan , , , a; Hassan et al.
Basic to many such tests is the simultaneous testing of the pest organism under the same conditions as the natural enemies to determine whether differences in susceptibilities exist. Usually, pests are less susceptible to pesticides than are their natural enemies. Methods for such screening range from laboratory tests, through semi-field tests to field studies. Laboratory methods include treatment of natural enemies through ingestion of pesticide or pesticide-treated materials, topical application, and placement of natural enemies on freshly dried pesticide residues on surfaces on which natural enemies are forced to rest.
The slide-dip technique in which organisms are immersed in a pesticide solution is commonly used for tests with mites. Exposure to residues on test surfaces can involve glass, sand, or leaves as the test surface. Foliage may be sprayed in the laboratory or field, and used either immediately after drying, or after aging for various lengths of time under field or standardized laboratory conditions. Semi-field tests involve confining test organisms on parts of plants or whole plants, after treatment of foliage with pesticides. Field tests involve assessing impacts on natural enemy populations when whole fields or plots are treated with pesticide.
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In field tests, the use of small, replicated plots is often unsatisfactory because natural enemies are mobile and poor separation of treatment effects occurs. The use of large unreplicated plots, with repetition over time, often gives more satisfactory results Brown ; Smart et al. Methods used to express degrees of susceptibility to pesticide include the size of the dose that kills half of a sample of the test organisms LD Where organisms are not orally or topically dosed, but rather confined on a treated surface, the measure LC is used, which is the concentration of solution applied to a treated surface that kills half of the test organisms in a defined period of time usually 24 or 48 h , Tests which incorporate measurement of effects of pesticide residues of various ages aged under either natural or defined environmental condilions are especially helpful in defining the period of risk that particular species of natural enemies experience after a pesticide application Bellows et al.
The ratio of the LC values of the natural enemy and the pest, or that of the natural enemy to the recommended application rate for a pesticide is a useful comparative measure of the selectivity of a pesticide Morse and Bellows , Bellows and Morse Assessment of natural enemy performance ability to encounter and subdue prey successfully or, for parasitoids, to locate and oviposit in hosts is a better indicator of the total effect of pesticide residues than is mortality because it also incorporates the sublethal effects of pesticides on natural enemies.
Pesticides can be used in various ways that reduce contact with natural enemies Hull and Beers Effects of pesticides on natural enemies can be decreased by reducing the dosage applied Poehling Use of half or quarter rates of pesticides often provides adequate pest control while reducing natural enemy mortality. The physical characteristics of pesticide formulations influence their impact on natural enemies, Granular formulations applied to the soil, for example, do not contact natural enemies on foliage or in the air and hence many natural enemies are unaffected by such applications Heimbach and Abel Systemic pesticides do little direct damage to natural enemies which do not consume plant sap and thus do not contact the pesticide Bellows et al.
Pesticides that kill only if ingested, rather than by mere contact with the integument, are less likely to harm natural enemies Bartlett Stomach poisons such as some pathogen-derived materials, plant-derived materials or mineral compounds are usually not damaging to predators and parasitoids which do not eat plant tissues. The extent of the area treated with pesticides can be adjusted to reduce exposure of natural enemies.
For instance, the treatment of alternate rows instead of entire blocks in apple orchards controls mobile orchard pests, but allows greater survival of the coccinellid mite predator Stethorus punctum LeConte Hull et al. DeBach successfully controlled purple scale, Lepidosaphes beckii Newman , in citrus by applying oil to every 3rd row on a 6-month cycle.
This provided satisfactory control of the pest without destroying natural enemies of other citrus pests. Contrarily, Carter found that strip spraying of cereals in Great Britain did not provide satisfactory control of aphids when strips were 12 meters wide because the natural enemies did not colonize the sprayed strips in time to suppress aphid resurgence. Contact between pesticides and natural enemies can be limited by using either nonpersistent materials, making less frequent applications, or applying materials in periods when natural enemies are not present or are in protected stages.
Using nonpersistent pesticides reduces damage to natural enemy populations because natural enemies that emerge after toxic residues have declined from inside protective structures such as cocoons or mummified hosts can thus survive. Also, natural enemies that arrive from untreated areas can recolonize treated fields sooner. Persistence of pesticides varies greatly. Materials such as diazinon or azinphosmethyl leave residues on foliage and other surfaces for more than one week at levels that kill natural enemies.
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Some herbicides, such as the triazines, applied to soil last for months. Other materials, such as the insecticide pyrethrin, degrade in hours or days. Weather conditions affect persistence of pesticide residues. Rain is most important as it can wash residues off surfaces, and temperature may influence both the toxicity of the pesticide and the rates of dissipation and degradation of residues.
Adjustment of timing of pesticide applications to protect natural enemies is a matter either of reducing overall spray frequency so that there are times when the crop foliage is not toxic to natural enemies, or changing the exact timing of particular applications to avoid periods when natural enemies are in especially vulnerable life stags. This system conserved the parasitoid, while the previous approach of direct pesticide-applications at the first generation of cereal leaf beetle larvae the stage attacked by the parasitoids did not.
Efforts to redirect pesticide applications to periods when natural enemies are less vulnerable may require that natural enemy populations be monitored to determine when susceptible natural enemy stages are present, with the goal of creating pesticide-free times around critical periods. Monitoring methods have been employed to detect adults of some parasitoids to aid in their integration into crop management systems as, for example, with parasitoids of California red scale, Aonidiella auranti, on citrus in South Africa Samways and parasitoids of San Jose scale, Quadraspidiotus perniciosus Comstock , in orchards in North Carolina U.
Mc Clain et al. If many pesticide applications are required, it becomes increasingly difficult to avoid periods when natural enemies are in vulnerable life stages. Options for the conservation of natural enemies are increased when the need for repeated use of broad spectrum pesticides is eliminated through the development of nontoxic pest control methods such as use of natural enemies or other methods including traps, mating disruption with pheromones, and cultural methods.
Reduced frequency of pesticide use in a crop is likely to greatly increase the survival and population densities of natural enemies, as in pear Pyrus communis L. Where pesticides are applied to crops and no sufficiently selective material or method of application can be discovered, attempts have been made to release and establish pesticide-resistant strains of key natural enemies. Pesticide-resistant strains of several species of phytoseiid mites have been developed by laboratory selection or recovered from field populations, including Metaseiulus occidentalis Nesbitt Croft ; Hoy et al.
Resistant strains of parasitic Hymenoptera have also been isolated from field populations and resistance levels to some pesticides further augmented by laboratory selection. Species have included an aphid parasitoid Trioxys pallidus Haliday, Hoy and Cave , a leaf miner parasitoid Diglypbus begini [Ashmead], Rathman et al. Studies of these organisms have demonstrated that for many natural enemies genetic variability exists that permits the development of pesticide-resistant populations under field or laboratory selection. In several instances, it has been demonstrated that these strains can establish and survive for one or more years in commercial fields or orchards where pesticide applications are made Hoy b; Hoy et al.
Long term persistence of the resistant strain is needed if economic costs of strain development are to be offset by prolonged benefit. In some cases, such as the use of Phytoseiulus persimilis for mite control in greenhouse crops, no susceptible strain is present, and it is sufficient merely for the resistance to last for the life of the crop usually months , because new predators will be released in future crops Fournier et al. In outdoor crops, maintenance of the resistant strain may require regular pesticide application. Where such applications are employed, introductions of pesticide resistant natural enemies can lead to their replacement of existing, pesticide-susceptible species Caccia et al.
In the absence of such ongoing pesticide usage, the introduced strain of resistant natural enemy may be displaced by other, pesticide-susceptible species Downing and Moilliet The importance of the level and sustained nature of pesticide selection to the establishment of resistant strains of natural enemies in the field has been pointed out by Caprio et al. In some cases, the need for continued treatments in the field to retain resistance in natural enemies may be met by pesticide treatments made for other pests in the crop system, Trials in Great Britain with an organophosphate-resistant strain of Typhlodromus pyri showed survival of the predator in orchards treated with organophosphate insecticides at levels sufficient to control Panonycbus ulmi Koch and Aculus schlechtendali Nalepa.
In a pyrethroid-treated orchard this strain of T. Pyri was scarce and did not suppress pest mites Solomon et al. Crop production systems based on biological control seek to use pesticides as supplements to natural enemies, not substitutes for them. Emphasis on obtaining a high level of pest control from pesticide application is likely to be detrimental when biological control agents are part of the system.
If pesticides, of whatever degree of physiological or ecological selectivity, are used at rates and frequencies designed to provide the first and basic means of control, natural enemy populations are likely to be too disturbed by loss of their host or prey to provide any significant level of control in the system. They state that the ability to predict and control organisms in a socially and economically desirable way is central to successful biological control strategies. Two considerations in biological control work are 1 a proposed biological control scheme manageable in a biological sense; that is, do the organisms behave in predictable and reliable ways; 2 can the organisms be manipulated in ways that are socially and economically feasible.
This question raises issues in social sciences, politics and philosophy. Although biological control researchers have had a history of successful practice, advocates of this approach to pest control believe their knowledge has not been fully utilized. Since the discovery of DDT's insecticidal properties in , researchers in biological control have been sensitive to the competition with chemical control. They feel that the failure of biological control to be more widely adopted originates from social and economic issues rather than from a failure of biological knowledge.
To explore how social and economic factors affect biological control it is necessary to define the meanings and scope of social and economic factors. The definition of biological control itself is contested, and it is important to state clearly the definition used in an analysis. Political economy examines the interactions between how resources are created, distributed and used, and the exercise of power and control. One can see the links between economic and political power that derive from ownership of factories and machines.
The owners, either individuals or corporations, decide what will be made, how the product will be distributed and how the proceeds from the sales will be allocated. The power of ownership is not absolute, but compared to the work force the owners have more power within the boundaries of the manufacturing plant. This power and wealth can be used to influence the general political process of a country and is more influential than that exercised by the non-owner groups. Similarly, ownership of land creates power to make economic decisions that affect the welfare of the work force and of consumers of the lands' products.
The creation and use of scientific and technological knowledge have attributes similar to the creation of other forms of wealth. Research and development occurs in laboratories and field stations that are owned and controlled by corporations, government agencies or universities.
The researcher has more autonomy than a factory work, but this should not obscure the employer-employee relationship that exists between the working scientist and the laboratory administration. The ability of a researcher to work depends critically on convincing the administration that proposed research would yield a useful product, or knowledge that the administration wants to have created.
Once developed, the scientific or technical knowledge may be owned and controlled by the administration. On the other hand, the knowledge may become part of the public domain and transfer to economic decision makers who have interest in and influence with the laboratory administration. Pest control has been developed principally in agricultural research stations, public health laboratories and the private chemical industry.
Biological control has been developed almost exclusively within agricultural research stations, which are supported by government and universities. Biological control information is largely non-proprietary and in the public domain. Although since some aspects of biological control knowledge have been developed by private, profit-seeking firms, the contributions of these companies are small.
Despite the free appearance of biological control knowledge, it would be wrong to assume that issues of power and control were not involved in the creation of this expertise or that future developments in biological control will be remote from questions about the exercise of political power. Commercial agriculture is becoming increasingly competitive, and farmers, particularly in North America, have had productive capacities in excess of markets.
The result is that farmers have been in an economic race to use the best technology to lower production costs and increase profits. Biological control must be applied to this highly competitive farm industry. Some research has addressed problems of urban, forest and public health issues, and such are expected to expand in the future. But, much of the political fortune of biological control will continue to be based on an ability to serve the farming industry.
Other forms of pest control technology compete with biological control in the sense that farmers usually have options among several technical practices. Farm managers, legislators, executives and university administrators will be attuned to the abilities of biological control expertise to function commercially. The exercise of political power around biological control research will revolve about the abilities of the expertise to function within the economic framework of agricultural enterprise that produces for a competitive, global market.
Part of understanding how social and economic factors affect biological control involves understanding the resource allocation process for biological control research. The allocation process is political and influential parties try to direct research resources in ways that will protect and enhance their interests. These questions center on the goodness of fit of the new technical knowledge to the complex of operations involved in agriculture. Is the technology cost effective?
Can the user receive training and advice on how to use it? Is the new technology compatible with the user's other production practices? Does the new practice fit within the user's traditional activities. Does the new practice fit the habits of how the user relates to government authority, presumptions and traditions? Does the new user have to adopt new assumptions about nature or the state to feel positive about trying the new knowledge?
From a practical stand point, the biological method may be arbitrarily divided into two sections: First , is the introduction of new entomophagous insects which do not occur in the infested region; and second , the increasing by artificial manipulation, of the individuals of a species already present in the infested region, in such a way as to bring about a higher mortality in their host than would have occurred if left to act under normal conditions.
Since , researchers have expanded and refined the definition of biological control. Recently the scope and content of the definition have become important public policy issues. This expanded definition has not been accepted by the Division of Biological Control, University of California, Berkeley, because the COSEPUP definition fails to provide essential and clear distinctions between different pest control technologies Garcia et al.
It was suggested that the essence of biological control was best described in a definition by DeBach Difficulties Encountered in the Measurement of Biological Control. Unfortunately, the ability to trace research and implementation in biological control are limited, especially when attempting to quantify the trends, as is discussed in other sections. It is possible to make quantitative estimates of research output and personnel levels in biological control for some periods and world areas. Quantitative estimates of research output, levels of research support and number of scientifically trained personnel engaged give only partial insights into the success of a scientific enterprise.
Qualitative considerations are important to assessing a research area. Prominent governing factors are the goals and methods involved, the quality of training, morale, the location of the institutional base within the framework of power and the relationships between scientific personnel and their clients pest control decision makers who must ultimately use the knowledge generated.
The number of scientific papers published, personnel and amounts of funds expended on biological control research do not always indicate the quality of a research operation. Complex considerations surround our ability to understand the fate of biological control at the implementation stage. Unfortunately, social and economic information gathered in listing successful biological control events is limited to the amount of damage done by the pest before and after the biological agent was introduced.
The difference between the before and after damages are then considered to be the value of the biological control agent. Such figures are often impressive, because some examples of biological control show enormous returns for small amounts of money invested. Insights into the factors affecting the use of biological control, however, are difficult to draw from such studies because the behavior of all the organisms involved is not established and the interests of the pest control decision makers are often confounded with those of the biological control researcher.
Such confusion is understandable because in classical biological control the researcher and the implementor are often the same person. If classical biological control were the only valuable mode of biological control then we would not be concerned with factors affecting decision makers such as farmers. Only the forces governing the amount of research in biological control would be considered because farmers would be the recipients of a new technology that is delivered to them without their having to take positive action.
Augmentative and conservatory biological control, however, are now substantially shifting the form of biological control technology. Implementation of biological control through augmentation and conservation of natural enemies is virtually certain to require changed behaviors on the part of a pest control decision maker who is different from the researcher. In such cases the behavior and interests of the implementor must be distinguished from the scientist, or it will be impossible to analyze the factors affecting implementation.
It must be known, for example, how the decision maker formulates long term goals. What sort of knowledge inputs are likely to appeal to the aspirations, experience and constraints within which the decision maker works? To what extent do economic factors interact with more subtle social, political and philosophical considerations? Failure to understand the actions of decision makers will lead to frustration for researchers and policy makers who believe that biological control offers substantial benefits.
Trained personnel, supportive institutions and funds are required for research. Sources of public and private funds are primary social and economic factors affecting the research enterprise in biological control. Past performance indicates that the biological control research community is a vigorous and vital group generating new results, conceptual and methodological tools and successful control schemes. These indicators include 1 the output of literature in biological control, 2 the staffing levels in research organizations, 3 the signs of intellectual vigor in institutions essential to biological control research and 4 the introduction of exotic species in programs of classical biological control see section on case histories.
Some educated guesses may be obtained, however. BNI has been published regularly since , and the number of abstracts published per year is the only global estimate available for the size of the worlds's biological control literature. The number of abstracts may be constrained more by budget limitations of CAB than by the number of literature entries available. The BNI database provides a minimal estimate of scientific activity in biological control. Since the average number of abstracts per year in BNI has been 2, The some 2, literature messages which are produced in biological control per year is of interest because it allows a rough estimate of the number of scientist years involved in the biological control research enterprise.
If it is assumed that one full time efficient scientist can produce messages per year, then a production of 2, messages per year implies that the world has at least , scientist years working in biological control. Many personnel involved are part time in their research activities, so more individuals are involved than scientist years. In addition the estimate of messages per year for the average scientists cannot be verified and some work in biological control does not result in publication.
Research in biological control is thus about 0. Agricultural science resources are not evenly distributed over the world, and historically agricultural research was conducted primarily in industrialized countries. It is not unexpected, therefore, that biological control researchers are concentrated in certain areas. A recent report of the U. Department of Agriculture estimated that ca. After a low in , the fashion of doing research in biological control began to climb again, and the proportion of entomological papers now devoted to biological control is ca.
Confirmation that enthusiasm for research on insecticides eclipsed biological control work was also noted by Price-Jones who sampled articles from the Journal of Economic Entomology. Similar conclusions were reached by Perkins in a study on how the introduction of DDT to the United States affected research by American economic entomologists. Perkins analyzed the changes in direction of one American research entomologist in the 's and 's and concluded that the technical capabilities of insecticides were responsible for a strong shift in research interests away from biologically based means of control towards chemically oriented technologies.
Before this time there were no more than papers in biological control in any one year. Developments in organizations and research also indicate that biological control is gradually being vitalized. The CAB International Institute for Biological Control is the largest multinational network of scientists engaged in biological control research. It was reorganized in to make it more useful to a wider range of clients Anonymous a. The Institute currently operates on ca. Department of Agriculture is the world's largest agricultural research organization. It has made substantial changes in its biological control effort during the past 50 years.
It had an active program of foreign exploration that was reduced during World War II. For 15 years no effort was made to revive the former program, but in plants to expand the work, primarily in augmentative biological control, were made. A major laboratory began operations in Perkins , and the USDA in the 's began a comprehensive effort to rationalize and coordinate biological control work USDA , Another example of continuing vitality in biological control is seen in the number of publications appearing in Entomophaga , which has been published in France by the International Organization for Biological Control since This journal is supplemented by publications such as the Chinese Journal of Biological Control since and Biocontrol News and Information since Some of the new companies supplying biological control agents are oriented towards the production and sale of long recognized biological control agents, such as Bacillus thuringiensis Berliner and Trichogramma spp.
Three new areas of study have increased the scope of biological control research. In biological control research was almost entirely confined to the use of insects to control insect pests and, in a few cases, to control noxious plants. The methods used were largely those of classical biological control: Additionally, work before World War II had demonstrated the utility of indigenous natural enemies. Rudimentary ideas began to emerge during the 's and 's concerning the need to use insecticides in ways that would not interfere with the suppressive power of insect natural enemies.
Nevertheless, the field of biological control was largely classical and research was oriented toward finding new natural enemies that would provide dramatic suppression of a pest comparable to that shown by the Vedalia beetle against the cottony cushion scale. At least three new areas of research have developed since the 's: Plant pathogens to control weeds are an active area of research. There were 55 projects cited involving the use of pathogens, including bacteria, fungi, nematodes and viruses. Five of these projects were considered operational. Water hyacinth control by Cercospora rodmanii Conway reached the stage of pilot tests by the United States Corps of Engineers in A second new field is the use of biological control for the control of plant pathogens.
The expansion of biological control into the field of plant pathology represents a new arena for biological control. Integrated pest management which heavily involves biological control, is a promising approach. IPM as a pest control strategy was profoundly influenced by classical biological control Perkins , but it is doubtful that IPM's roots helped encourage research in biological control between National Science Foundation removed classical biological control from the large research project, "The Principles, Strategies and Tactics of Pest Population Regulation and Control in Major Crop Ecosystems," in favor of research on the ecological theory of why and how biological control works Huffaker Thus, the first major research effort in IPM was handicapped by not building one of the component techniques for pest suppression into the basic design of the new research.
Systems analysis and computer modeling were favored instead. Combining biological control with pesticide use was the cornerstone on which the concept of integrated control was founded Perkins , but later definitions of IPM obscured the importance of biological control. The current definition of IPM does not mention biological control, or any other specific control technology explicitly: In recent years, researchers have begun to ask whether biological control ought to be seen as fundamental to IPM, and to receive the funding levels appropriate to such a critically important technology.
Work on biological control must be built into IPM research from the beginning if biological control practice is to be successful. Therefore, biological control must be developed and implemented as a component of IPM. However, if it is to be an integral part of IPM along with plant resistance, cultural methods and pesticidal controls biological control must be nurtured to become a strong vital entity.
Such indicators suggest that whatever factors govern the research in biological control, they are moving in favor of biological control. Complex social phenomena are impossible to attribute precisely to clear causes, but several seem particularly relevant since the early 's. Some arise from events removed from the activities of the biological control workers, but others are due to the activities of the research community. Scientific research requires resources, so it is not surprising that the amount of research in biological control is highly correlated with the gross domestic product GDP of a country.
Productivity of research in biological control correlated with GDP indicates that this form of research is similar to others in the sense that wealthy countries do more of it. Correlation between a country's wealth and its research productivity does not, however, reveal everything about the ways in which each country may decide how much and what kind of biological control research to perform.
Moreover, the data suggest that some countries are particularly high in their productivity of biological control research given their GDPs e. Explanations for why some countries are high producers compared to others are not obvious, but one possibility is that membership in an international network such as CIBC is conducive to productivity in biological control research.
Therefore, countries such as Australia, India and Canada, all long term members of Commonwealth Institute of Biological Control, are comparatively high. Conversely, countries that are not in coordinated networks may have research productivities considerably below what the sizes of their economies might suggest.
France and Japan have GDP's 2. Another possibility to explain high interest in biological control in countries like Canada and Australia is that both areas were subject to European invasion.