The emergence of resistance problems not only shortens the lifespan of currently available insecticides but also undermines the efficacy of newly discovered or developed insecticides owing to cross-resistance and multiple resistance mechanisms In addition, data on insecticide use for vector control are extremely important to design appropriate pesticide management systems on judicious use, resistance management, and reduction of risks to human health and the environment However, a recent global survey drew attention to critical deficiencies in the capacity to manage vector control insecticides.
It includes the lack of pesticide registration guidelines, gaps in pesticide procurement practices, and a lack of expertise of vector control decision makers 80 , These shortcomings could heavily hamper the optimal selection and use of insecticides and application methods for vector control heavily undermine the effectiveness and safety of operations Indeed, there is always a considerable risk of resistance evolution, especially when the insecticides are indiscriminately misused or over-used.
Risk Factors for Resistance Development in Soybean Aphid
The main objective of effective insecticide resistance management programme is to prevent or delay the evolution of resistance, or assist to retrieve the susceptibility status in which insecticide resistance has already been well-established. For instance a single mosquito can reproduce several thousand progenies within a couple of weeks Indeed, no single prescription can be offered to forestall resistance under any conditions. There are hundreds of different insect pest species that are under chemical control, and each species represents several distinct combinations of biological and ecological characteristics.
Management by moderation should be the basic approach and should be supplemented to the maximum possibly by integrated pest management measures Interestingly, there are several different strategies that have been proposed to tackle the insecticide resistance crisis. Indeed, IVM is a rational decision-making process to optimize the use of resources for vector control. The main objective of the IVM approach is to contribute to the achievement of the global targets set for vector-borne disease control, by making vector control more efficient, cost effective, ecologically sound and sustainable with the available tools and resources.
In the face of current challenges to vector control, the IVM approach is vital to achieve the national and global targets set for vector-borne disease control In addition, the rotation of chemically different classes of insecticides has been tested and the use of novel insecticides alone 84 , 85 or in a mosaic with existing insecticides 86 has also been proposed.
The early attempts in using entomopathogenic fungi as microbial control agents against insect pests were overshadowed by the development of numerous potential chemical insecticides. However, currently, to address the insecticide resistance by means of biological control agents like the entomopathogenic fungi such as Metarhizium anisopliae and Beauveria bassiana have also been advocated A recent study demonstrated the importance as well as potentiality of the combination of permethrin and entomopathogenic fungi as vector control interventions against the insecticide-resistant An.
It is important to note that it also exhibited a significant level of synergistic effect on malaria vector mortality and it could prevent or delay the resistance development substantially. Howard et al. It provides an opportunity to kill insecticide resistant mosquitoes more quickly than the susceptible ones. Therefore, it could serve as one of the ideal tools to tackle the resistance crisis under the field conditions.
This could lead to an effective resistance management without further application of insecticides. It is one of the most promising techniques, as fungal infection kills the vector mosquitoes at a slower rate than the conventional chemical insecticides. IRM is used to describe practices aimed at reducing the potential for insect pests to become resistant to a pesticide. Kerr 91 attributed the resistance development rate to the frequency of resistance genes, the nature of the genes, generational turnover, and the intensity of selection pressure.
The first three factors are indigenous to the population and beyond control. Regarding the fourth factor, Georghiou 92 and Brown 93 suggested several methods whereby selection pressure might be reduced, and henceforth to postpone the development of resistance.
Implications and Prognosis of Resistance to Insecticides | SpringerLink
Today, resistance management in the context of integrated pest management has evolved as the favored approach to prevent, delay, or reduce the impact of insecticide resistance. Subsequently a quick decision has been made to change to fenitrothion an organophosphate with a different mode of action, for IRS. This alternative intervention has removed the selection pressure and reduced the frequency of resistance. As a result, the recent susceptibility tests showed that the frequency of resistance genes in the vector population had dropped below the level of detection, and pyrethroids were once again introduced into the IRS programme, albeit on a more limited scale.
It clearly suggests that the resistance genes can be eliminated from the vector population by removing the selection pressure. To fully develop this strategy, a thorough knowledge of insecticide resistance mechanisms is extremely essential.
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Resistance monitoring and evaluation are critical elements of vector control programme and their impacts are essential to understand the progress, challenges and success of disease control. If, resistance is once established in a vector population, there is a genuine threat of the resurgence of vector-borne diseases that had been presumed to be under control and by the time such resistance is detected, it is often far too late.
Therefore, focusing on continuous insecticide resistance surveillance and monitoring is extremely essential to react proactively Indeed, bioassays are the primary tool for the resistance monitoring, but they must be supplemented by molecular and biochemical assays wherever resistance is detected Vector control can be targeted against larvae and adults of insect vectors and it may differ in countries and even regions within the same country. Therefore, it must be selected more cautiously by considering the existing epidemiological and entomological tools like susceptibility status, population dynamics, vectorial capacity, feeding preference, and major disease transmission season of local insect vectors to sustain in the long-run.
It could serve as a valuable tool to predict the transmission potential, and selection of practical operational tools for planning and management of vector control programmes, tailor-made for local settings. However, currently, the lack of entomological capacity in vector control programmes is one of the major hindrances to implement effective insecticide resistance monitoring and surveillance in malaria control.
Therefore, it is extremely important in all National Malaria Control Programmes NMCPs to establish capacity for basic entomological monitoring, by appointing senior medical entomologists or train entomologists wherever necessary, and establish the necessary infrastructure for basic entomological surveillance. In addition, adequate fund also must be allotted to establish the necessary capacity for the vector control programme At the moment, people are appreciating and insinuating the use of plant-based insecticides as pest control agents to control insect vectors and pests.
It has ceased the tendency of heavy reliance on chemical insecticides to reduce negative impacts on human health and the environment Although, the usage of plant-based pesticides is a part of tradition and culture in the developing countries, over the past three decades there has been a tremendous dedication and commitment to develop plant-based ideal pesticides or green pesticides by various researchers. As a result we have evaluated over thousands of plants as potential pest control agents in terms of insecticidal, antifeedant, repellent, oviposition deterrent, growth regulatory and antivector activities.
However, only a few plant-derived botanicals such as neem, lemon grass, etc have demonstrated their broad effectiveness against various insects. Therefore, development of next generation vector control tools is extremely important particularly formulating new plant-based insecticides in terms of cost-effective, user-environmental friendly with new mode of action. Malaria is a disease of poverty inflicting a serious negative impact on health and socioeconomic development in the poorest countries of the world that cannot afford to succeed Presently we have minimized the global malaria burden considerably, by inducting the low-cost interventions like ITNs.
Control of the vector mosquitoes has been an integral part of efforts to either eliminate or control the disease worldwide.
Revista de la Sociedad Entomológica Argentina
In West Africa, where the main vectors are members of the An. In West Africa, resistance to pyrethroids due to knockdown resistance kdr mutations in An. Resistance of An. The number of available and effective pesticides for malaria vector control is also reported to be decreasing.
However, vectors developing resistance against pyrethroid is already a serious threat to sustain the continuous use of ITNs and IRS. Although 12 insecticides are currently recommended by the WHO for IRS, they belong only to four different chemical classes namely organochlorines, pyrethroids, carbamates, and organophosphates, and the cross-resistance among insecticides is often frequent. The widespread use of the same insecticides in the agricultural sector has made the situation worse. Insecticides that can be used in malaria control are becoming increasingly limited.
Introduction of inappropriate insecticides without a proper understanding of the prevailing resistance mechanisms may lead to enhanced vector resistance and vector control failure. Early detection and knowledge on the resistance status and the underlying mechanisms in vector mosquitoes are essential for effective long-term control of the vector.
The current success of these strategies in reducing the occurrence of malaria, contributed towards the optimism that elimination of this disease which is a major public health problem is a feasible objective. The number of countries that employed IRS as vector control strategy has increased from 31 in to 68 in In Africa, LLINs and IRS are now being deployed in a large-scale more than ever before, which considerably exposes African vectors to enormous selection pressure for insecticide resistance.
Unfortunately, since the introduction and commercialization of the pyrethroids in the s and s, little public investment has been observed in insecticides for public health purposes. Therefore, the majority of this selection pressure comes from the pyrethroid insecticides. These are the only class of insecticides currently applied to treated nets and most commonly used for IRS application Therefore the widespread as well as indiscriminate usage of pyrethroid insecticide increases the risk of resistance.
The situation may be accelerated by the reintroduction of DDT in several countries of Africa as cross-resistance between these classes of insecticides which can occur as a result of amino acid substitutions in the shared target sites. All major malaria vectors in Africa have developed resistance to these insecticides and the resistance alleles appear to be spreading at an exceptionally rapid rate Inheritable resistance traits develop by selective pressure exerted on a mosquito population.
Fast-acting insecticides exert strong selection pressures, and the short generation time and prolific progeny characteristic of the mosquito lifecycle is well suited for quick development of resistance. Over 50 species of Anopheles are reported to be resistant to insecticides Insecticide resistance in the vector Aedes aegypti is an important but under research, and poorly understood phenomenon. Several early reports of DDT resistance, in the s to s, reported cross-resistance between DDT and pyrethroids. Later literature suggests that organophosphate resistance is also developing in some areas.
The impact of this resistance on operational activities such as larviciding and space spraying is largely unknown. Resistant populations of Aedes aegypti have been detected in several countries throughout the geographical range of this species and, in some areas; the evolution of insecticide resistance has been linked to the failure of the dengue control programme.
Very little is known about the molecular or biochemical basis of this resistance and yet such information is needed to identify the origin of resistance and develop suitable strategies to reduce its spread and minimize the impact of resistance mutations. Certainly, IRS programmes should avoid the practice of spraying the same class of insecticide repetitively year after year. Instead, another opportunity is to spray insecticides with different modes of action alternately and alternating different insecticides in space, as a mosaic in rotation , Combination of interventions involves using different insecticide classes applied in different forms within a house e.
In the case of larval control, there is only one which is currently recommended, organophosphate, temephos, which could be used in rotation or as a spatial mosaic with other larvicidal agents Therefore, such combinations are likely to play a vital role in the future insecticide resistance management programmes It is important to understand that almost all public health insecticide classes are also used in agriculture and it substantially contributes to some degree of the resistance problem in malaria vectors.
In the developing countries farmers obtain insecticide from the public health personals engaged in the indoor residual spraying and use for agricultural pest control. For example in Ethiopia, although DDT has been totally banned for agriculture pest control, a recent study reported that DDT has been extensively applied by the farmers as a pesticide, which has been procured illicitly through the black market at a low-cost 7.
The evolution of high gene frequencies of resistance is most commonly associated with IRS. It is interesting to note that numerous numbers of insecticides are currently available in the market for agricultural pest control rather than malaria vector control.
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Therefore, the agricultural sector has many choices for the selection of various kinds of appropriate insecticides and must avoid using the insecticides of public health importance. It is desirables for both the agriculture and public health sectors to work together for sustainable insecticide resistance management. However, it demands further research to understand the influence of different agricultural and domestic pesticide uses on emergence and spread of insecticide resistance which are important to public health Currently there is a lack of alternative, cost-effective and safe insecticides.
The development of new, alternative insecticides is a high priority, but is an expensive and long-term endeavor. Indeed, it is essential that novel alternative insecticides belonging to new or different classes be developed if current scaling-up efforts are to be sustained and if local interruption of malaria transmission is to be achieved.
Principles of Pest Management
Above all, new classes of insecticides with novel mode of actions are urgently needed; especial insecticide products are suitable for use on bed nets. Furthermore, it is also essential to preserve and prolong the susceptibility and effectiveness or life of the currently available insecticides, which will involve new formulations designed for resistance management In the recent years, an encouraging progress has been made to develop insecticides with new active ingredients to manage insecticide resistance. Innovative Vector Control Consortium IVCC has already developed an impressive pipeline for reformulations of existing insecticides, and the ongoing search for new active ingredients is promising.
The new formulation makes the insecticide more effective on more challenging surfaces, such as traditional mud used in house building in rural African communities, and reduces IRS programme costs by increasing the required interval between applications. The new formulation not only increases the residual performance of the insecticide, but also provides an effective tool to control pyrethroid resistant mosquitoes in the field. But greater investments are urgently required to speed up the research and development process Besides, promoting appropriate and alternative eco-friendly vector control technologies like use of botanical pesticides may reduce the use of hazardous insecticides 5 as well as minimize the insecticide resistance in the future.
Otherwise, the recent advances will be rapidly jeopardized, especially in the case of indoor residual spraying, which tends to lose its efficacy as soon as vectors become resistant. At present, malaria control relies heavily on a limited arsenal: artemisinin derivatives and pyrethroids.
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