Natural and Engineered Pest Management Agents
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Due to cross-resistance among similar Bt proteins, the effectiveness of the pyramid strategy in Brazil as a resistance management tool has been limited thus far Bernardi et al. Cross-crop resistance is another concern in diverse crop landscapes where multiple crops share similar Bt proteins. Research results suggest that if cross-crop resistance occurs among different Bt crops, landscapes like Brazil where corn, cotton, and soybean share similar Bt proteins, the selection period for cross-crop insects will be extended and thus accelerate resistance evolution Yang et al.
Therefore, rapid resistance evolution with pests like S. Resistance management has a limited likelihood of success if GE products like those described above are not placed into a well-understood IPM framework capable of sustaining the value of these technologies. The potential utility and contribution of IPM tactics including cultural and biological controls need to be better understood. The industry has developed several initiatives to drive the implementation of refuges and best management practices BMPs with growers. Industry also developed several pilot programs with growers to educate and provide incentives for adopting refuge, though these have resulted in minimal uptake to this point.
Although research continues to refine management tactics to use with GE and non-GE refuge crops, tropical geographies like Brazil that harbor pests like S. Socioeconomic factors should be combined with agricultural systems knowledge to develop an industry framework that drives adoption of key IPM and IRM practices. In addition, regulation that requires critical resistance management tactics like the planting of refuges should be pursued.
Until either or both of these approaches are further developed, deploying new GE technologies in countries like Brazil should proceed with caution. Common bean Phaseolus vulgaris L. BGMV is the causal agent of the most destructive viral disease of common beans in Brazil. It is efficiently vectored by the whitefly, B. BGMV causes stunted growth, yellowing and flower abortion, and high yield losses Anderson et al. Traditional pest control tactics for the insect vector are limited to chemical pesticide application, and overuse of pesticides on common beans is a common problem leading to environmental effects and insect resistance problems Bonfim et al.
GE common bean offers an opportunity to farmers to control this viral pathogen without chemicals. However, there remain several key challenges for successful integration of this technology into a sustainable IPM plan. Following regulatory approval, the current challenge is to successfully insert this GE trait into commercial varieties that are optimized for the different regions Souza et al. Additionally, IPM and farm management practices are being optimized and farmer training is being offered to ensure sustainable use and durability of the trait.
For example, management strategies including implementing a whitefly host-free period elimination of hosts for both virus and whitefly , designating sentinel areas where common bean fields are planted early in the season to screen for the presence and abundance of viruliferous whitefly populations , and optimizing planting time and chemical control practices are all valuable components of the emerging IPM plan.
These tactics are important to reduce damage by whitefly due to direct feeding as well as deposition of honeydew on which mold fungi can grow and reduce photosynthesis. Additionally, it is important to reduce areawide pressure of whitefly as a disease vector because, while BGMV is the most devastating virus, it is not the only whitefly transmitted virus to common beans Brown et al. Building professional capacity through farmer training, and developing an alert system to quickly identify if a threshold for pest population or viral pathogen load is being exceeded will also be critical to success.
Because the GE common bean varieties have not yet been commercialized, this work to optimize management practices and increase farmer training is being conducted with growers on small plots up to a half hectare. There have been encouraging results with implementing whitefly host-free periods and using an alert system to evaluate the real need for chemical control. GE common bean with resistance to BGMV will help to diversify the tool box for IPM in Brazil, and an integrated approach to pest management of whitefly is essential for achieving agricultural and environmental sustainability, food security and grower profitability.
IPM practices including whitefly monitoring, sentinel areas, pest free periods, etc. Weed management strategies have not changed greatly in the last five decades. Despite the adoption of GE crops with HT traits, weed management arguably is still largely, if not exclusively, based on herbicides. HT crops have many advantages, and the benefits of being able to use herbicides that would cause unacceptable phytotoxicity to a crop e. However, to date, HT traits are largely limited to conferring tolerance to a few herbicidal active ingredients, and a small subset of commercial commodity crops.
Therefore, many opportunities to expand the portfolio of HT traits in crops with this technology remain, considering that the availability of herbicides for use in high value crops such as fresh vegetables is limited. If HT traits were available in some high value crops, the effectiveness of weed control would improve greatly, the costs of weed control would decline and the quality of the crop would increase Gianessi, Despite the unprecedented success of HT technology for weed management, successful implementation and sustainability of this technology presents many challenges, including the evolution of herbicide resistance in key weed species.
Success of HT crops is seen as increased simplicity of weed management, improved time management and reduced costs; farmers as a result, became increasingly unwilling to adopt integrated weed management IWM practices including the need for multiple herbicidal modes of action to address evolved herbicide resistances in weeds Frisvold et al.
These challenges highlight the need for diverse, well-designed and proper IWM plans. It is important to recognize that herbicide resistance evolution is not necessarily a reflection on the cultivation of HT crops. Rather, herbicide resistance has been a prominent problem for agriculture since the beginning of herbicide use Heap, The issue of evolved herbicide resistance in key weeds reflects the fact that herbicides have been the principle tactic for weed control for more than 45 years and the inclusion of alternate strategies for weed management has declined steadily over the same period of time Jussaume and Ervin, ; Owen, For example, glyphosate has been applied on the majority of row crop acres in the US for more than two decades.
While there are many reasons and justifications for this approach including improved time management and efficiency, reduced costs for weed control, as well as increased effectiveness, simplicity and convenience, the ecologically narrow focus of one approach unsurprisingly resulted in rapid and widespread evolved resistance to glyphosate within important weed species such as Amaranthus tuberculatus J.
Sauer, A. Wats, and Conyza canadensis L. Cronquist Owen et al. This clearly demonstrates why weed management in row crops is not sustainable if based primarily on a single herbicide. Because herbicides will likely continue to play a significant role in weed management in the future, designing robust management plans for weeds will be important for sustainability of HT crops.
Unfortunately, strategies associated with IPM for insect pests are often not applicable for weeds Owen, , For example, concepts such as action thresholds for insect damage have no utility in weed management, given the growth plasticity of weeds, the high amount of seeds produced, and the long life of seeds in the soil seedbank. In fact, often the decision to allow weeds to remain uncontrolled because the population density is below a theoretic economic injury level at one point in time will result in greater weed problems in the future.
Similarly, IPM programs for insects and diseases are typically developed around one pest species; whereas for weed communities found in crop fields, many species, each with different ecological characteristics and management requirements need to be considered. For example, different weed species affect the crop at different times of the growing season which complicates the timing of control tactics. Furthermore, many weeds have numerous germination events, each of which requires control while insect pests tend to have fewer emergence events that simplifies the timing of control tactics.
Finally, with weeds, the pest targets are closer morphologically, phenologically, physiologically and biologically to crops than insect or diseases, which presents additional challenges and limits the flexibility of control tactics. Nevertheless, the need for sustainable and durable tactics for weed control is important. The development of an IWM strategy, which includes diverse tactics other than herbicides for weed control, complements the concept and foundational approach of IPM programs developed for other pest complexes Swanton and Weise, ; Swanton et al.
Diverse IWM strategies include, but are not limited to, cultural and biological tactics that can supplement mechanical and herbicide-based weed management approaches and will be important components of successful weed management programs in the future Meissle, ; Owen, Examples of diverse strategies that supplement an herbicide-based weed management plan include, but are not limited to harvest weed seed destruction Walsh et al.
Related to seed destruction for example, Walsh et al. Similarly, Blackshaw et al. While it may be simpler to depend on a few weed management practices, the key to sustainability will be for all entities involved in weed management, private, commercial and government, to consider more diverse weed management approaches.
The plan provides guidelines for establishing management programs for herbicide-resistant weeds and consists of pilot projects demonstrating community-based weed management. However, the specifics of the conceptualized diverse and community-based management plans for herbicide-resistant weeds have yet to be developed and implemented. Herbicide resistant weeds are very mobile within an agricultural community, and while local solutions should be adaptable to an individual grower's needs, they must align with the broader weed management goals at a landscape or regional level Ervin and Jussaume, Confounding the effort to manage those weeds are multiple herbicide resistances in a majority of key weed populations Owen et al.
While some farmers may recognize the importance of community involvement with regard to herbicide resistance management, some feel that any efforts put forward will be for naught, as their neighbors will not participate in the effort Doohan et al. For decades, the dominant paradigm—that weed mobility is low relative to insect pests and pathogens, that there is an ample stream of new weed control technologies in the commercial pipeline, and that technology suppliers have sufficient economic incentives and market power to delay resistance supported a laissez faire approach to herbicide resistance management.
Earlier market data bolstered the belief that private incentives and voluntary actions were sufficient to manage resistance.
USA - Insect diagnostic and control compositions - Google Patents
Unless there is a community-based effort put forth to manage herbicide resistance that goes beyond using herbicides, it is unlikely that any effort will be successful. Therefore, while GE crops may offer great opportunities for weed control in agriculture, there remains a critical need to adopt diverse tactics other than herbicides to manage resistant weeds and to reduce the risk of herbicide resistance evolution where it has not yet become a problem.
The goal of an IPM strategy is to support the sustainable production of high quality crops while minimizing environmental impacts attributable to pests or pest management practices. While the benefits of using an IPM approach are evident, as outlined in the case studies above, implementation of IPM can be very challenging for several reasons Box 1 Meissle, One common theme among the case studies presented is that a successful IPM or IWM strategy leverages a diversified approach. As can be seen based on the many years of experience using Bt and HT traits, insects and weeds will inevitably evolve resistance over time.
Part of the goal of the IPM plan is to diversify the approaches to pest management, and limit the dependence on one single technology. Just as it is crucial for IPM practices including whitefly monitoring, sentinel areas, pest free periods, etc. Knowledge and understanding of the technology, pest, crop, region, alternative tools and even social contexts are critical for the success of an IPM plan, because if there is insufficient understanding of the technology and how best to integrate it into an IPM system, the durability of the technology may fail.
In addition, if there is not adequate training and engagement of farmers to recognize the short- and long-term benefits of the management plan, the technology may fail due to lack of compliance. Incentives may be needed to gain producer compliance with best management and resistance management requirements, and often farmer training is needed to demonstrate the short-term and long-term benefits of implementing a sustainable approach. Box 1. Challenges and solutions for successful implementation of an integrated pest management IPM approach.
Likewise, training stakeholders about how best to integrate and use GE crops in their existing agricultural system is critical. While industry tends to focus on discovery, research and development and promoting the value of GE traits, there is a huge responsibility for institutions e. As suggested by Stern et al.
On the other hand, if the technology and tactics are fit to the existing system, and appropriate training is provided to stakeholders, there is a much higher chance of success and sustainability over time. Because of these and other challenges for successful implementation of an IPM approach, pest control based on broad spectrum chemicals is often perceived as the easier, more economic, and most efficient short term approach used for pest management in large-scale farming operations.
To promote continued research, expand implementation, and highlight the value of using an IPM strategy, a joint effort among governments, label organizations, growers, grower associations, and the seed and pesticide industries is critically needed. Most of the major successes in gaining grower support for resistance management over the past 50 years were preceded by pest resistance-related economic failures and the solutions involved a strong partnership between industry, regulators and farmers. Innovative solutions and BMPs aimed at sustainability must continue to be developed in particular for crops and regions where there is high resistance risk e.
The benefits of a successful IPM strategy, including reduced application of broad spectrum chemical pesticides, more durable pest management in ecologically balanced crop production systems, and reduced risks to human health and the environment, are clear. Sustainable, eco-rational IPM strategies rely on a diversified portfolio of tactics, of which GE crops represent a valuable tool.
By leveraging the experiences gained with GE crops, understanding the limitations of the technology, and considering the successes of GE traits in IPM plans for different crops and regions, we can enhance the durability and versatility of IPM plans for future crops. All authors listed have made a substantial contribution to the conceptualization and drafting of the manuscript. All authors contributed to manuscript revision, read and approved the submitted version. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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A wicked view. Weed Sci. Bernardi, D. Cross-resistance between Cry1 proteins in fall armyworm Spodoptera frugiperda may affect the durability of current pyramided Bt maize hybrids in Brazil. Blackshaw, R. Ongoing development of integrated weed management systems on the Canadian prairies. Blanco, C. Current situation of pests targeted by Bt crops in Latin America.
Insect Sci. Boller, E. Bonfim, K. RNAi-mediated resistance to Bean golden mosaic virus in genetically engineered common bean Phaseolus vulgaris. Plant Microbe Interact. Brookes, G. The global income and production effects of genetically modified GM crops GM Crops and Food 4, 74— Global income and production impacts of using GM crop technology — GM Crops Food 7, 38— Brown, J. Revision of Begomovirus taxonomy based on pairwise sequence comparisons. Long-term regional suppression of pink bollworm by Bacillus thuringiensis cotton. Choudhary, B.
Google Scholar. Cornell University Cruz, I. A Lagarta-do-cartucho na Cultura do milho. Dasgupta, S. Working Paper Washington, DC: World Bank. Davis, A. Are herbicides a once in a century method of weed control? Pest Manage. G APS Features CrossRef Full Text. Dhurua, S. Diez-Rodeiguez, G. Dively, G. Regional pest suppression associated with widespread Bt maize adoption benefits vegetable growers. All improved root growth of grape and radish and inhibited root elongation of ryegrass and lettuce but had no effect on cucumber [ 92 ]. In a study of the effect of TiO 2 nanoparticle on aquatic life, the result raveled that TiO 2 reduced the light to entrap the algal cell and thus reduce the growth [ 94 ].
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Any disturbance in these relationships may lead to undesirable result. One of the most effected factors that play great roll in this disturbance is the application of different types of pesticides. The potential for misapplication and accidental exposure is great [ 64 ]. The runoff from agriculture and urban land, and rain precipitation and dry disposition from the atmosphere, can transport pesticides to streams and groundwater [ 96 ].
Birds, aquatic organism, and animals are under the threat of harmful pesticides. The soil is an important part of the environment and plays an effective role in other parts. The application of pesticides results into two ways: positive way by destroying the specific target and negative way by transferring to another non-specific target.
Pesticides that were detected in the atmosphere are I organochlorine insecticides resistant to environmental degradation , II organophosphate insecticides not long lived in the environment , III atrazine herbicides heavily used herbicides, persistent in the environment , IV acetanilide herbicides used heavily, but not as persistent as atrazine [ 71 ].
Mobility may result in redistribution within the application site and sometimes off-site. After application, a pesticide may I attach to soil particles, vegetation, or other surfaces and remain near the site; II attach to soil particles and move with eroded soil in runoff or wind; III dissolve in water and be absorbed by plants, overflow, or leach; IV pass off in vapor or erode from foliage or soil with wind and become airborne [ 99 ]. Also, the mobility of pesticides can be affected by several factors of pesticide sorption, water solubility, vapor pressure, and other environmental and site characteristics including weather, topography, canopy, ground cover, soil organic matter, texture, and structure [ 99 ].
The persistence of pesticide is expressed in terms of half-life that can help estimate whether or not a pesticide tends to build up in the environment. Pesticides with shorter half-lives tend to build up less and less likely to persist in the environment, while pesticides with longer half-lives are more likely to build up after repeated application. Higher persistence increases the risk of contamination of nearby surface water, groundwater, plants, and animals. Anonymous [ 88 ] reported that some pesticides stay in the soil long enough to be absorbed by plants grown in the field years later.
The behavior of pesticides in soil is governed by a variety of complex dynamic physical, chemical, and biological processes, including sorption-desorption, volatilization, chemical and biological degradation, uptake by plants, runoff, and leaching [ , ]. Biopesticides have benefits and limitation effects on the environment, human life, or agricultural product. They are highly effective in managing pests and diseases, without creating negative impacts on the environment, and their active and inert ingredients are generally recognized as safe.
Besides the microbial content, carrier media for formulating biopesticide were consisted of several organic materials, such as animal broth, organic materials, or organic waste product. The media is a biodegradable material. In addition, biopesticides support stability and sustainability of agroecosystem because they did not affect negatively on the environment [ ]. The nanoagrochemical is crucial to modern agriculture, and due to their direct and intentional application in the environment, nanoagrochemical may be regarded as particularly critical in terms of possible environmental impact, as they would represent the only intentional diffuse source of engineered nanoparticles in the environment [ ].
There is harmful chemical reaction and contamination by nanoparticles to soil ecosystem and change in soil structure due to their large surface area and Brownian motion [ 45 ]. AI clothianidin was rapidly released from the nanocarrier systems and that the durability of three nanoformulations would be short in water as well as in soil. Nanoparticles can easily be released in the water body or air, and uptake by living organisms creates toxic effect for humans and animals [ 43 ]. Pesticides are essential to improve the production of crops. The quantity of pesticides will continue to increase as long as the use of pesticides increases.
Despite the tremendous benefits of pesticides for human beings especially in agriculture fields, side effects and undesirable results of pest managements such as pesticide residue crop products that are used in feed lead to several human illnesses in soil and water, microflora in soil, and ecosystem in general. The book inspired public concern about the toxicity in wildlife, contamination, and the increasing pest resistance.
Control of regulated or quarantined pests is typically done through prevention of entry to a country or an area, eradication and containment, and use of tools such as biological control, pesticides and biopesticides, plant resistance, cultural methods, and natural enemy encouragement. In a review suggested that classical biological control has provided and should continue to provide many positive outcomes for dealing with damaging invasive alien insect pests [ ].
Genetically modified GM food is a new type of potentially safer food without the use of pesticides; crops producing pesticides substance from genetic material that has been added to the plant. To insure safety, the EFSA Panel on Genetically Modified Organisms GMO require scientific risk assessment on the possible risk they might present for humans, animal health, and the environment before being authorized for market placement [ ].
The approach is to compare transgenic crops and derived products with similar conventional ones that are already known and considered safe for use, based on recognized practices, harmonized methods, and data sharing facilitated through the WG-SNFF [ ]. Maximizing pesticide efficiency requires the use of radiolabeled pesticides to study pesticide metabolism, fate, residues, and formulation [ ]. An increasing number of countries started to develop control strategies for the use of pesticides. The Danish National Action Plans on pesticide — strategy were 1 authorization of pesticides, 2 targeted inspection efforts, 3 collection of knowledge via the pesticide research program, and 4 information, advice, and guidance.
The Report of the OECD Workshop on Sustainable Pest Management in Practice: Anticipating and Adapting to Changes in the Pesticides Regulatory Landscape status and subsequent availability of agricultural pesticide products are necessary for sustainable pest management, including the use of registered agricultural pesticides. In general, the consequences of regulatory decision and the entailing process of adaptation of the agricultural production are not widely considered within the registration process. Regulators, pesticide manufactures, and pesticide users in OECD member countries have had to adapt their practices to ensure that sustainable and effective pest management options remain possible.
These changes reduce risk to human health and the environment while promoting sustainable agriculture [ ]. The Secretariat [ ] in their 34 sessions includes recommendation that: The international community must work on the development of a comprehensive, binding treaty to regulate hazardous pesticides throughout their life cycle. It should cover standardization among countries, policies to reduce pesticide use worldwide, and development of a framework for the banning and phasing-out of highly hazardous pesticides, as well as strict liability on pesticide producers.
Development of comprehensive national action plans to support alternatives to hazardous pesticides along with binding and measurable reduction targets and time frames. While pesticides proved effective in mitigation of harmful bugs, the risk associated with their use has exceeded their beneficial effects. Nonselective pesticides can harm nontarget plants and animals along with the targeted ones; also with repeated use, some pests develop genetic resistance to pesticides [ 97 ].
To control the use of pesticides and reduce their effects, registration is an important aspect of pesticide management to ensure that the pesticide products released in the market are authorized and used only for their planned purpose. To reduce pesticide impact on the environment, minimize contamination, and ensure the safety of human sources of food and water surface and groundwater , users should be: Practicing IPM.
Considering application site characteristics and location of wells, ponds, and other water bodies. Preventing back siphoning and spills, leaving buffer zone around sensitive areas, and reducing off-target drift. Storing pesticides and disposing of wastes securely and safely [ 98 , 99 , , , , , , , , , , , , , , ]. Biopesticides have attracted attention in pest management in recent decades and have long promoted as prospective alternative to synthetic pesticides [ 68 ]. It is expected that biopesticides will equalize with synthetics in terms of market size, between the late s and the early s [ ].
Also, Soesanto [ ] The conclusion of biopesticides was that biopesticides are the best way to control plant pathogens because of their beneficial effects; though there are still many limitations to be reduced, biopesticides supported stability and sustainability of agroecosystem because they did affect negatively on the environment.
Nanotechnology is the new type of IPM providing a promising future in the direction of formulation that can be used to improve the stability and effectiveness of natural product [ , ]; it provides controlled release of the molecules at the site of action, can minimize potential toxic effects on nontarget organisms, and can prevent degradation of the active agent by microorganisms [ , ].
Nanotechnology that includes nanopesticides seems to have a promising future in IPM. The potential toxicity of these nanoparticles is not standardized and not well understood yet explored by international and national safety regulators [ 60 , , , ]. Nanopesticides are more complex products by design and therefore pose greater challenges to analysts [ 30 ]. Continuous growth in population around the world leads to increase the demand for higher crop production. The quality and quantity of crops provided to people must be satisfactory, which can be achieved by using specific methods to control pests that play a great role in crop losses and poor product.
The main method used for this purpose is synthetic pesticides, with other methods: biopesticides and nanopesticides. Despite the harmful side effects especially of synthetic pesticide compared to the other methods with less harmful effects on humans, plants, and the environment, still the synthetic pesticides play an important part of IPM. This requires intensive work of scientists, institutions of agriculture around the world, environment studies to assess and evaluate the side effects of these different methods, and provide good training for safer application of pesticides and also continues studies for every new chemical production and methods used in the agriculture field, to decrease and minimize the harmful effects on humans, animals, plants, nontarget organisms, and the environment, including aquatic environment.
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Our readership spans scientists, professors, researchers, librarians, and students, as well as business professionals. Downloaded: Abstract Mankind depends on agricultural products for food consumption. Keywords pesticides classification of pesticides pesticide hazards future of pesticides. Introduction Agriculture is the primary source for human food; it provides different kinds of crop production. Cultivation practices, such as crop rotation intercropping or under sowing.
Physical methods, such as mechanical welders: Natural products, such as semichemical or biocidal plant extracts Biological control with natural enemies, including different pathogens of plants Decision support tools to inform when it is economically beneficial to apply pesticides and other controls Ghandler et al [ 28 ] reported that although pesticides act similarly despite their chemical active group. Pesticides in agriculture and their benefits The farmers around the world had used different methods and ways to fight the causes that lead to reducing crop yield, most of these methods were simple and traditional, and the result were not satisfactory until the use of pesticide application started.
Controlling human and livestock disease vector nuisance organisms. Preventing or controlling organisms that harm other human activities and structures. Classification of agrochemical pesticides 4. Toxicology of pesticides Widespread use of pesticides is a significant source of air, water, and soil pollution causing risk to human health as a result of misuse or accident as well as leaving lasting harmful chemicals in the environment [ 63 ]. The WHO [ 46 ] grouped pesticides according to the potential risks to humans caused by accidental contact to human being to five classes: Class Ia. Extremely dangerous parathion, dieldrin.
Class Ib. Highly dangerous eldrin, dichlorvos. Class II. Moderately hazardous DDT, chlordane. Class III. If any populations of feral Gossypium spp. EPA analyzed the possibility of gene flow from transgenic cultivars expressing Bt to wild native plants which acquire the Bt genes through cross pollination as part of its risk assessment of Bt potato, Bt corn, and Bt cotton as summarized above.
For Bt cotton, where the possibility of gene movement may exist in certain geographically distinct areas, EPA has mitigated the potential for such movement by imposing strict geographic restrictions on the sale and distribution of Bt cotton. Hazard to non-target organisms is a function of toxicity AND exposure. Non-target organisms that are not exposed to a toxic substance are not at risk. Organisms that may be exposed to limited amounts of a toxic substance may also not be at risk. Therefore, the risk assessment process depends on determination of the toxicity of a given substance and the degree of environmental exposure of non-target species.
The primary issue that defines the type of toxicity data needed for a risk assessment of PIPs is that the pesticidal substance is contained within the plant parts thus resulting in minimal exposure to non-target organisms. This exposure scenario is quite different from spray applications of pesticides. Therefore, each risk assessment is made from an analysis of the nature of the gene being introduced, the plant receiving the gene, the environment where the plant will be grown and the species susceptible to the effects of the introduced gene.
This amounts to a case-by-case analysis. In addition, the concentration of the active ingredients in plant tissues, soil residues and their degradation rates, are also measured to more accurately determine exposure of non-target organisms. If necessary, higher tier testing to assess population level effects is performed. The following basic ecological effects testing requirements on representative non-target terrestrial and aquatic species listed in the Harmonized Pesticide Test Guidelines are addressed by submission of data or waiver requests with credible justification:.
Chronic, reproduction, life cycle and population effects and host range testing. If the results from environmental fate studies show a plant protein that is toxic to non-target species persists in the environment at significant levels, Tier III studies are designed to show effects of chronic exposure to these levels on selected fish and wildlife species.
Tier III studies are also used to determine non-target effects of plant proteins designed to inhibit insect molting, reproduction, disease resistance and similar properties. Simulated or actual field testing however, field scouting for non-target insect abundance is currently recommended as a Tier I test. OPP recognizes the potential value of Tier IV field tests as an additional check on the presence of ecosystem effects. Therefore, field data are being gathered concurrently with full-scale efficacy testing during the product development stage. This provides the opportunity to evaluate pesticidal effects both direct and indirect on a much broader spectrum of non-target species under more natural exposure conditions than is possible in single species no-choice laboratory feeding studies.
An additional factor in determining the extent of testing necessary for risk assessment is the degree of pest species specificity shown by the protein in question. This is of primary importance in assessing ecological risk. Most protein plant-incorporated protectants produce adverse effects against a specific class of target species. Careful scientific consideration on a case-by-case basis is given to the selection of non-target species to be tested in order to include species that are most likely to be susceptible.
Selection of the test species for any specific plant construct is done jointly by the Agency and the registrant during pre-registration conferences. Rationale for selection is discussed and the final test species list may be smaller or greater than the guideline data requirements. The selection of test species is limited by their availability, the ability to rear them in captivity-in sufficient quantities for testing, or their ability to survive captivity without unacceptable mortality levels.
Endangered and threatened species hazard is addressed by extrapolating toxicity from related species, and if a hazard is identified, after consultation with the Fish and Wildlife Service possible risk is mitigated by preventing field exposure. Wherever possible, the whole modified plant tissue or pollen is used as the dosing substance. The use of pure test substance alone may be inadequate since it does not test for inadvertent, possibly harmful changes in the plant tissue itself i.
In addition to the general data requirements discussed above, data derived from additional tests may be required by the Agency in order to make judgments regarding safety to non-target organisms on a case-by-case basis. Such data may also be required where special problems with Tier I testing are encountered. Test methods will usually be derived from protocols already described or cited in Harmonized Guidelines, or other sources, such as the OECD Guidelines, or new protocols may be developed on a case-by-case basis.
Soil organisms may be exposed to d-endotoxins from current transgenic crops by exposure to roots, incorporation of above ground plant tissues into soil after harvest, or by pollen deposited on the soil. Root exposure may occur by feeding on living or dead roots or, theoretically, by ingestion or absorption after secretion of d-endotoxin into the soil. In addition, evidence suggests that some soil components, e. Therefore, exposure to d-endotoxin bound to soil particles may also be a route of exposure for some soil.
Experiments addressing the amounts and persistence of d-endotoxins in the soil have been submitted and reviewed for the current registrations. A number of publications in the scientific literature have also addressed the degradation of Cry proteins in the soil. These experiments consist of the incorporation of purified d-endotoxin or transgenic plant material in soil in a laboratory setting. Cry protein half-life studies were submitted for registration for corn containing Cry1Ab, and published studies were available for Cry1Ac cotton.
Cry1Ab produced estimated degradation rates of 1. Data produced by Monsanto for Cry1Ac protein and transgenic Cry1Ac in cotton give degradation rates of approximately days for the purified protein, and 41 days for the protein in cotton tissue. Published data for Cry1Ab or Cry1Ac in cotton tissue or as purified protein produced degradation rates of 2. Degradation rates of purified Cry1Ac in two different non-sterile soils were 22 d and 40 d Palm et al.
None of the studies discussed above have been performed under field conditions, although most have used field soil in laboratory microcosms. Several studies indicate that Cry proteins bind to clays and humic acids Crecchio and Stotzky , Koskella and Stotzky , Tapp and Stotzky , Tapp and Stotzky , Stotzky a. The results of these studies suggest that this binding slows the rate of microbial degradation of these toxins compared to when these soil components are not present Stotzky a.
However, this protection is not absolute, since degradation does in fact occur under several experimental conditions. Several factors influence either the affinity of binding or the rate of degradation. In particular, pH near neutrality generally substantially increases degradation.
At pH above 5. Potato prefers acid soils Smith , and the optimum range is pH 5. The optimal range for cotton is pH 6. Therefore, under most production conditions, cotton and corn would not be grown on soils that would inhibit the rate of degradation compared to what is seen at near neutral pH. On the other hand, potato may be grown at soil pH levels that approach those in which a substantial reduction in degradation rates has been shown to occur. However, effects of pH on degradation rates in the range of pH 5. Studies have shown a substantial degradation loss of biological activity occurring rapidly in the first several weeks, with much slower subsequent breakdown Tapp and Stotzky , Palm et al.
These experiments suggest that testing for persistence in the field should be determined over sufficiently long periods to assure an accurate assessment of degradation. Many of the experiments examining persistence of Cry proteins reported in the published literature have apparently been conducted in bulk soils or soil components. Bulk soil generally does not support populations of microorganisms as high as in the rhizosphere or where plant residues are incorporated into the soil.
Therefore, degradation rates under field conditions may be higher than those shown in bulk soil experiments. It is important to consider that a number of factors are expected to influence persistence under actual field conditions, including:. Since these factors may vary considerably in the field, persistence of Cry proteins could likewise vary considerably.
However, the conditions examined by the registrants generally replicate common field soil conditions, although performed in a laboratory setting. Consideration should be given to performing field tests of degradation under a range of conditions that may be expected under actual Bt crop cultivation. A previously unconsidered issue regarding exposure of soil organisms to Cry proteins concerns the possibility that one of the Bt crops, specifically Bt 11 corn, exudes Cry1Ab protein into the soil Saxena et al.
Exudation would likely cause continuous exposure of soil organisms to Cry1Ab protein. This situation differs from previous risk assessment considerations, which examined the effects of a single incorporation of Bt plant material or Cry protein, as would occur with incorporation at the end of the growing season. It is also possible that soil organisms could be exposed to higher levels of Cry1Ab than would occur with a single incorporation.
Finally, since only Bt 11 corn was examined, it is unknown whether the proposed exudation could occur in other Bt crops. Since it is difficult to correlate the relevance of the published laboratory studies to field situations, the SAP recommended field studies be conducted in established Bt fields in a variety of soil types and climatic conditions. The SAP suggested that the amount, accumulation and persistence of biological activity of Cry proteins in the soil are areas that should be investigated. However, the SAP also concluded that this data was not necessary for an EPA preliminary risk assessment but may be needed for a final assessment.
In general, the Panel believed that studies on the mechanism Cry proteins enter soil e. Knowledge of the potential environmental impacts is the important issue. Most available data do not suggest toxic effects on non-lepidopterans from Cry1Ab or Cry1Ac proteins, or of non-coleopterans by Cry3A, even at doses from about 10 2 to 10 4 fold higher than the amounts estimated from the Saxena et al.
A published longer term continuous feeding study using transgenic cotton containing either Cry1Ab, Cry1Ac, or potato containing Cry3A at an estimated concentration of PPM were performed on the collembolan Folsomia candida and the orbatid soil mite Oppia nitens Yu et al. No adverse effects were detected in these studies for any of the three Cry proteins. Therefore, high dose and continuous feeding studies on several invertebrates, including several important soil species, do not indicate likely adverse effects on non-lepidopteran species in the field.
The route of exposure of non-target organisms must also be considered. In the case of significant root exudation of Cry protein, some differences in exposure compared to single incorporation of transgenic plant material may be expected. Organisms that pass soil through their digestive systems, such as earthworms, could be exposed to higher levels of Cry protein due to exudation compared to a single incorporation of plant material.
Organisms at higher trophic levels that feed on soil feeders may, secondarily, be exposed to toxin. Testing on birds and rodents however, showed that there was no toxicity to these species. It is very difficult to determine the importance of shifts in the structure of microbial soil populations unless these changes can be associated with measurable ecological parameters.
In most cases, such research has not been performed for microbial populations. Limited data do not indicate that Cry proteins have any measurable effect on microbial populations in the soil. Small transient changes in microbial populations have been associated with some Bt transgenic plant material cotton rather than the transgenic Cry protein itself in experiments where transgenic plant tissue was used Donegan et al.
The authors of the study suggested that the process of making the transgenic plant, e. Other work comparing transgenic Cry3A potato and the non-transgenic isoline found no significant difference on the populations of several groups of soil microorganisms including fungal species diversity and three plant pathogenic fungi in this season long field study Donegan et al.
Primary exposure to soil organisms has been considered to be from incorporation of crop residues at the end of the growing season, or to a lesser extent from deposition of pollen onto the soil. Therefore, degradation and possible accumulation of Cry proteins has been examined by determining degradation rates of Cry proteins, either in isolation or as expressed in the plant tissue, incorporated at a single point in time. In addition, determination of degradation rates of Cry proteins in soil is more feasible using a discreet starting point.
Estimates of total Cry protein incorporated into the soil have been based upon the biomass of total plant tissue, although it is not clear whether root biomass has been included in these calculations. In contrast, the roots of a crop may be comparable in biomass to the above ground portions of the crop at the end of the growing season. During the growing season, soil organisms are exposed to roots and their contents. In particular, organisms that feed on living roots will ingest expressed Cry protein directly from this source. Data for expression levels of Cry proteins in the roots are not available for all registered transgenic crops.
Cry3A is expressed in potato tubers at 1. An average of Because of the variability of expression levels between transformation events, the levels of root expression in the other transgenic Bt crops cannot be predicted from these numbers or from expression in other tissues in those plants. Similar to the case with above ground plant tissue, organisms that feed on root feeding organisms may be exposed indirectly and over an extended period of time.
In addition, a significant amount of root tissue has been estimated to be lost during plant growth. Estimates of loss of root tissue range from about percent of total root tissue and about percent for rhizodeposition of insoluble root material into soil Newman This dead tissue may consist of exuded high molecular weight materials such as root cap mucilage, root cortical cells, or whole root tissue Newman The composition of this material is generally believed to consist largely of higher molecular weight materials, such as the structural components of the roots.
It is therefore difficult to estimate whether the proportion of Cry protein in this material differs from that of living roots. Deposition of some Cry protein in the soil will likely occur during degradation of root tissue, in addition to Cry protein incorporated into the soil from the above ground parts of the crop at the end of the growing season. As with the above ground portions of the plant, the root biomass increases during the growing season.
Use and Impact of Bt Maize
Therefore, assuming that other factors are comparable, exposure of soil and soil organisms will be minimal early in the growing season and will increase with root volume. As discussed above, several soil invertebrates have been used to examine the toxicity of Cry proteins. Submitted studies have examined high dose acute toxicity to earthworms and collembola, while published studies have examined the effects of longer term exposure to collembola, orbatid mites Yu et al.
Also discussed above is new unpublished data Stotzky b that indicates no apparent impact on a range of soil microorganisms, total biomass, etc. Results of all these studies have revealed little or no adverse effects. The adequacy of these studies should be considered in the context of exposure during the growing season to root material, as well as incorporation of above ground material and roots at the end of the growing season. In particular, studies with all Cry proteins currently found in transgenic crops, and examining adults and offspring of the collembolan Folsomia candida and the orbatid mite Oppia nitens , both detritus feeders, showed no adverse effects at expression levels at or above those found in the above ground parts of the plant Yu et al.
An additional study conducted by Saxena and Stotzky reported that Bt Cry protein released from root exudates and biomass of Bt corn has no apparent effect on earthworms, nematodes, protozoa, algae, bacteria, actinomyces and fungi in soil in spite of the fact that enough detectable Cry protein is bound to soil particles to show toxicity to the target pest. In addition, toxicity studies of above ground invertebrates, discussed elsewhere, also show few adverse effects to taxa that are not closely related to those known to be affected.
While not soil organisms themselves, these data generally suggest the lack of substantial adverse effects to soil invertebrates. Available studies on the impact of transgenic Cry producing plants indicates that adverse effects on soil microorganisms are unlikely. No effects have been seen due to the protein itself, and only a minimal, transient increase observed in soil microbes attributed to the transgenic cotton plant tissue rather than the Cry protein expressed in that tissue Donegan et al. No adverse effects have been observed in a similar season long field study with Cry3A potato Donegan et al.
US5643776A - Insect diagnostic and control compositions - Google Patents
Concern has been expressed about the possible transfer of transgenes from crop plants to related or unrelated species of plants or other organisms. Also of concern is the possibility of horizontal gene transfer that is transfer to unrelated species. Horizontal gene transfer, regardless of the source of the gene, has been considered in the literature, and evidence presented for possible impact on the evolution of organisms over long periods of time Smith et al.
However, the likelihood of such transfer over a human time scale, and where the transgene has a positive impact on the fitness of the recipient, has not been demonstrated. Horizontal transfer of several traits might be of concern for the current Bt crops, for example the cry genes and antibiotic resistance genes.
There is no evidence that horizontal gene transfer occurs from plants to microbes or bacteria to bacteria. Bt genes which naturally occur in many soils have never demonstrated horizontal gene transfer. The SAP suggested the determination of the amount, concentration, and persistence of biological activity of Cry proteins in the soil are areas that should be investigated.
The EPA agrees with the SAP that actual field data on Cry protein levels in soil will yield relevant data on persistence and natural variation of plant-produced Bt proteins in soil. If high levels of Cry proteins are found in field soils, reevaluation of the risks to certain non-target organisms might be required. Therefore, EPA is requiring additional supplementary studies regarding Cry protein in soil.
The Agency is requiring testing of Cry1Ab and Cry1F protein under a range of conditions typical of Bt corn cultivation. EPA requires each registrant or the registrants in cooperation to submit test protocols before the studies are actually conducted. In general, the Agency anticipates that soils would be sampled from fields where Bt corn has been grown continuously for at least 3 years compared with fields where no Bt crop has been grown. These paired fields would include several locations throughout the corn growing area of the US representing different soil and climatic variations.
The Agency anticipates that samples would need to be taken 2 or 3 times during the growing season. Insects, fungi, and weeds developing resistance to pesticides are well documented in agriculture. As resistance begins to develop, more pesticide is needed to achieve control until total failure of that pesticide occurs. Insect resistance management IRM is the term used to describe practices aimed at reducing the potential for insect pests to become resistant to a pesticide.
Academic and government scientists, public interest groups, and organic and other farmers have expressed concern that the widespread planting of genetically transformed plants will hasten the development of resistance to Bacillus thuringiensis Bt endotoxins. Sound IRM will prolong the life of Bt pesticides and adherence to the plans is to the advantage of growers, producers, researchers, and the American public. The goal of IRM is to have the target pest continue to be susceptible to the pesticide.
Each IRM program consists of strategies to reduce the likelihood that insect resistance will develop and strategies to manage insect resistance once it occurs. Bt IRM is of great importance because of the threat insect resistance poses to the future use of Bt microbial pesticides and Bt plant-incorporated protectants.
Effective insect resistance management can reduce the risk of resistance development. The elements are: knowledge of pest biology and ecology, dose level of toxin expressed in the Bt crop , refuge design and deployment non- Bt plants producing Bt -susceptible insects , cross-resistance between different Bt proteins, effective field monitoring for insect resistance, remedial action if resistance occurs, integrated pest management, development of alternate modes of action, and grower education. For example, how far do the larvae move within the field and how far do the adults move affects the distance between the refuge and the Bt crop.
The susceptible insects from the non- Bt refuge need to be in close enough proximity to randomly mate with the resistant insects that emerge from the Bt fields to produce heterozygous offspring that are fully susceptible to the Bt protein. Additional important questions that need to be addressed are how many generations of insects are produced each year, what is the mating behavior and the oviposition behavior, what is the host range of the insect, population dynamics, pest ecology, and if possible, the genetics and mechanism of resistance and the frequency of resistance alleles in the insect population.
In addition, how the crop is grown including other pest management practices, when it matures, the extent of the acreage, and the overlap in distribution with other Bt crops are all important in the development of an appropriate program. Current resistance management programs for Bt plant-incorporated protectants PIPs are based on the use of both a high Bt toxin concentration coupled to the use of structured refuges planted nearby to provide sufficient numbers of susceptible adult insects.
It also assumes that there will be a low initial resistance allele frequency and that there will be extensive random mating between resistant and susceptible adults.
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