Potential role of microbial pathogens in control of red palm weevil (Rhynchophorus ferrugineus) ‐ A Review

The invasive Red Palm Weevil (RPW), Rhynchophorus ferrugineus (Olivier) (Coleoptera: Curculionidae), is one of the most destructive pests of ornamental and economically important palms globally. It has been found in 50 % of date‐growing and 15 % of coconut‐producing countries in the world. Synthetic organic insecticides have been the default method to combat this pest, but they are clearly inefficient due to the secretive nature of the insect and there is concern about non‐target effects from blanket spraying. For this reason, there is increasing interest in biological control methods such as the possible use of microbial entomopathogens, which might be incorporated into IPM approaches. In this review we summarize research work on microbial control agents, their effectiveness against RPW and their integration with other control measures.     

In silico designing of insecticidal small interfering RNA (siRNA) for Helicoverpa armigera control

Helicoverpa armigera, a polyphagous lepidopteron insect pest causes severe yield loss in cotton, legumes, tomato, okra and other crops. Application of chemical pesticides although effective, has human health and environmental safety concerns. Moreover, development of resistance against most of the available pesticides is compelling to look for alternative strategies. Adoption of Bt transgenic crops have resulted in reduction in pesticide consumption and increasing crop productivity. However, sustainability of Bt transgenic crops is threatened by the emergence of insect resistance. In the present study potential insecticidal siRNA were identified in six H. armigera horrhonal pathway genes. Out of over 2000 computationally identified siRNA, 16 most promising siRNA were selected that address the biosafety concerns and have high potential of targeted gene silencing. These siRNA will be useful for chemical synthesis, in insect feeding assays and knockdown the target H. armigera hormone biosynthesis, consequently obstructing the completion of insect life cycle. The siRNA have a great potential of deployment to control H. annrmigera alone as well as with Bt for insect resistance management.     

Molecular mechanisms of insect adaptation to plant defense: Lessons learned from a Bruchid beetle

Plants can accumulate, constitutively and/or after induction, a wide variety of defense compounds in their tissues that confer resistance to herbivorous insects. The naturally occurring plant resistance gene pool can serve as an arsenal in pest management via transgenic approaches. As insect‐plant interaction research rapidly advances, it has gradually become clear that the effects of plant defense compounds are determined not only by their toxicity toward target sites, but also by how insects respond to the challenge. Insect digestive tracts are not passive targets of plant defense, but often can adapt to dietary challenge and successfully deal with various plant toxins and anti‐metabolites. This adaptive response has posed an obstacle to biotechnology‐based pest control approaches, which underscores the importance of understanding insect adaptive mechanisms. Molecular studies on the impact of protease inhibitors on insect digestion have contributed significantly to our understanding of insect adaptation to plant defense. This review will focus on exposing how the insect responds to protease inhibitors by both qualitative and quantitative remodeling of their digestive proteases using the cowpea bruchid–soybean cysteine protease inhibitor N system.     

Plant essential oils synergize various pyrethroid insecticides and antagonize malathion in Aedes aegypti

Pyrethroid resistance is a significant threat to agricultural, urban and public health pest control activities. Because economic incentives for the production of novel active ingredients for the control of public health pests are lacking, this field is particularly affected by the potential failure of pyrethroid‐based insecticides brought about by increasing pyrethroid resistance. As a result, innovative approaches are desperately needed to overcome insecticide resistance, particularly in mosquitoes that transmit deadly and debilitating pathogens. Numerous studies have demonstrated the potential of plant essential oils to enhance the efficacy of pyrethroids. The toxicity of pyrethroids combined with plant oils is significantly greater than the baseline toxicity of either oils or pyrethroids applied alone, which suggests there are synergistic interactions between components of these mixtures. The present study examined the potential of eight plant essential oils applied in one of two concentrations (1% and 5%) to enhance the toxicity of various pyrethroids (permethrin, natural pyrethrins, deltamethrin and β‐cyfluthrin). The various plant essential oils enhanced the pyrethroids to differing degrees. The levels of enhancement provided by combinations of plant essential oils and pyrethroids in comparison with pyrethroids alone were calculated and synergistic outcomes characterized. Numerous plant essential oils significantly synergized a variety of pyrethroids; type I pyrethroids were synergized to a greater degree than type II pyrethroids. Eight plant essential oils significantly enhanced 24‐h mortality rates provided by permethrin and six plant essential oils enhanced 24‐h mortality rates obtained with natural pyrethrins. By contrast, only three plant essential plants significantly enhanced the toxicity of deltamethrin and β‐cyfluthrin. Of the plant essential oils that enhanced the toxicity of these pyrethroids, some produced varying levels of synergism and antagonism. Geranium, patchouli and Texas cedarwood oils produced the highest levels of synergism, displaying co‐toxicity factors of > 100 in some combinations. To assess the levels of enhancement and synergism of other classes of insecticide, malathion was also applied in combination with the plant oils. Significant antagonism was provided by a majority of the plant essential oils applied in combination with this insecticide, which suggests that plant essential oils may act to inhibit the oxidative activation processes within exposed adult mosquitoes.     

Feasibility,limitation and possible solutions of RNAi‐based technology for insect pest control

Abstract Numerous studies indicate that target gene silencing by RNA interference (RNAi) could lead to insect death. This phenomenon has been considered as a potential strategy for insect pest control, and it is termed RNAi‐mediated crop protection. However, there are many limitations using RNAi‐based technology for pest control, with the effectiveness target gene selection and reliable double‐strand RNA (dsRNA) delivery being two of the major challenges. With respect to target gene selection, at present, the use of homologous genes and genome‐scale high‐throughput screening are the main strategies adopted by researchers. Once the target gene is identified, dsRNA can be delivered by micro‐injection or by feeding as a dietary component. However, micro‐injection, which is the most common method, can only be used in laboratory experiments. Expression of dsRNAs directed against insect genes in transgenic plants and spraying dsRNA reagents have been shown to induce RNAi effects on target insects. Hence, RNAi‐mediated crop protection has been considered as a potential new‐generation technology for pest control, or as a complementary method of existing pest control strategies; however, further development to improve the efficacy of protection and range of species affected is necessary. In this review, we have summarized current research on RNAi‐based technology for pest insect management. Current progress has proven that RNAi technology has the potential to be a tool for designing a new generation of insect control measures. To accelerate its practical application in crop protection, further study on dsRNA uptake mechanisms based on the knowledge of insect physiology and biochemistry is needed.     

The evolutionary origins of pesticide resistance

Durable crop protection is an essential component of current and future food security. However, the effectiveness of pesticides is threatened by the evolution of resistant pathogens, weeds and insect pests. Pesticides are mostly novel synthetic compounds, and yet target species are often able to evolve resistance soon after a new compound is introduced. Therefore, pesticide resistance provides an interesting case of rapid evolution under strong selective pressures, which can be used to address fundamental questions concerning the evolutionary origins of adaptations to novel conditions. We ask: (i) whether this adaptive potential originates mainly from de novo mutations or from standing variation; (ii) which pre‐existing traits could form the basis of resistance adaptations; and (iii) whether recurrence of resistance mechanisms among species results from interbreeding and horizontal gene transfer or from independent parallel evolution. We compare and contrast the three major pesticide groups: insecticides, herbicides and fungicides. Whilst resistance to these three agrochemical classes is to some extent united by the common evolutionary forces at play, there are also important differences. Fungicide resistance appears to evolve, in most cases, by de novo point mutations in the target‐site encoding genes; herbicide resistance often evolves through selection of polygenic metabolic resistance from standing variation; and insecticide resistance evolves through a combination of standing variation and de novo mutations in the target site or major metabolic resistance genes. This has practical implications for resistance risk assessment and management, and lessons learnt from pesticide resistance should be applied in the deployment of novel, non‐chemical pest‐control methods.     

Role of nanotechnology in agriculture with special reference to management of insect pests

Nanotechnology is a promising field of interdisciplinary research. It opens up a wide array of opportunities in various fields like medicine, pharmaceuticals, electronics and agriculture. The potential uses and benefits of nanotechnology are enormous. These include insect pests management through the formulations of nanomaterials-based pesticides and insecticides, enhancement of agricultural productivity using bio-conjugated nanoparticles (encapsulation) for slow release of nutrients and water, nanoparticle-mediated gene or DNA transfer in plants for the development of insect pest-resistant varieties and use of nanomaterials for preparation of different kind of biosensors, which would be useful in remote sensing devices required for precision farming. Traditional strategies like integrated pest management used in agriculture are insufficient, and application of chemical pesticides like DDT have adverse effects on animals and human beings apart from the decline in soil fertility. Therefore, nanotechnology would provide green and efficient alternatives for the management of insect pests in agriculture without harming the nature. This review is focused on traditional strategies used for the management of insect pests, limitations of use of chemical pesticides and potential of nanomaterials in insect pest management as modern approaches of nanotechnology.     

Symbiotic microorganisms: untapped resources for insect pest control

Symbiotic microorganisms offer one route to meet the anticipated heightened demand for novel insect pest management strategies created by growing human populations and global climate change. Two approaches have particular potential: the disruption of microbial symbionts required by insect pests, and manipulation of microorganisms with major impacts on insect traits contributing to their pest status (e.g. capacity to vector diseases, natural enemy resistance). Specific research priorities addressed in this article include identification of molecular targets against which highly specific antagonists can be designed or discovered, and management strategies to manipulate the incidence and properties of facultative microorganisms that influence insect pest traits. Collaboration with practitioners in pest management will ensure that the research agenda is married to agricultural and public health needs.     

Insect pest management in African agriculture: Challenges in the current millenium

Pest management on a global scale experienced a total revolution after World War II when synthetic organic compounds were in agriculture and public health. However, it soon became apparent that there were many limitations in the use of chemicals for pest management. In agriculture, problems of pest resurgence, secondary pest outbreaks, pest resistance and adverse effects of pesticides on the environment, including human poisoning and toxicity to other non-target organisms, led to the search for alternative approaches to the pest outbreak problem. The 1960s produced new ideas on integrated pest management (IPM) strategies, followed by intensification of the search for biological control agents, which could be incorporated into IPM programmes. New application technologies were developed in the 1970s and 1980s and ecological approaches to the pest problem were spearheaded in the developed world in the 1990s, with extensive studies focused on the whole ecosystem. Important advances in crop production have also taken place in Africa in this century, involving adoption of high yielding varieties, fertilizer application, intensification of crop protection approaches, less shifting cultivation and more mono-cropping systems. However, these advances have led to increasing pest problems which unless tackled imaginatively and intelligently, they could become the most important constraint in crop production in the present millennium. Africa has entered the current millennium with relatively underdeveloped agriculture on a global scale and little investment in research on new pest management technologies that could be used to reduce crop losses. We are still highly dependent on pesticides for pest management. Therefore, the greatest challenges in agriculture in Africa will be the switch from a pesticide based mode of reducing losses due to pests to one that is ecosystem based, making use of insect management techniques which are ecologically and economically sound. Specifically, some of the major challenges in pest management in agriculture in Africa include; (i) reducing the dependence on pesticides, thus avoiding the limitations observed in the past 50 years; (ii) overcoming ignorance of the pest species and their associated community of parasites and predators which has dire consequences on the whole ecosystem; (iii) keeping out exotic pests, which in this millennium have had a devastating blow on the production of some crops and (iv) developing indigenous technologies for pest management (IPM, biocontrol, etc.) and making available to farmers materials for pest management which are affordable, safe, effective and environmentally friendly (e.g. microbial, botanicals, pheromones, genetically engineered products etc.). Both legislative and quarantine measures will have a significant role to play in pest management in the next millennium, but only when practised on a wider geographical area. Information technology (IT) will affect the way we acquire and make use of pest management strategies. Africa is therefore faced with the challenge of building up and improving its infrastructure and expertise on IT if it is to benefit pest management on the continent.     

Towards the genetic control of insect vectors: An overview

Insects are responsible for the transmission of major infectious diseases. Recent advances in insect genomics and transformation technology provide new strategies for the control of insect borne pathogen transmission and insect pest management. One such strategy is the genetic modification of insects with genes that block pathogen development. Another is to suppress insect populations by releasing either sterile males or males carrying female‐specific dominant lethal genes into the environment. Although significant progress has been made in the laboratory, further research is needed to extend these approaches to the field. These insect control strategies offer several advantages over conventional insecticide‐based strategies. However, the release of genetically modified insects into the environment should proceed with great caution, after ensuring its safety, and acceptance by the target populations.     

Disruption of the chemical communication of the European agrobiont ground‐dwelling spider Pardosa agrestis by pesticides

Lycosid spiders are among the most abundant and diverse insectivores occurring in all agroecosystems. Certain pest management practices, such as the application of pesticides, can disrupt their role in insect pest control. Therefore, understanding the effects of pesticides, including sublethal effects, is essential for the assessment of chemical effects on beneficial arthropods. We investigated the sexual chemical communication of the beneficial agrobiont spider Pardosa agrestis and its disruption by two widely used pesticides, the glyphosate‐based herbicide Roundup and the pyrethroïd‐based insecticide Nurelle D. A two‐choice olfactometer and Y‐maze were used to study the effectiveness of female airborne and dragline pheromone cues and the disruptive effect of the pesticides. Males of P. agrestis did not locate females via airborne cues, but were very receptive to female dragline silk and male dragline silk. When both female dragline silk and male dragline silk were provided at the same time, the males preferred female silk. Pesticide treatments significantly affected the male ability to follow female cues deposited on dragline silk. The 3‐h residues of both Roundup and Nurelle D significantly disrupted the male ability to follow female cues deposited on dragline silk. Treatment by 48‐h residues significantly disrupted the male ability only in the case of Nurelle D. Our results demonstrate that pesticides reduce the ability of male spiders to search for a mate due to the disruption of the male's ability to detect the silk cues of the female.     

Species-specific responses of dew fly larvae to mycotoxins

Abstract   The larval stages of saprophagous insects and filamentous fungi have been demonstrated to be serious competitors on decaying organic matter. When filamentous fungi appear to be competitively superior, fungal mycotoxins have frequently been suggested to constitute chemical weapons, causing high mortality among insect larvae. In this study, we tested whether typical fungal secondary compounds can indeed be considered as the underlying mechanism of interference competition between filamentous fungi and various saprophagous Drosophila species. In contrast to our expectation, we found no grand mycotoxin-specific effects, but insect survival appeared to be generally determined by complex interaction between toxin identity, toxin concentration and insect species. Three out of five drosophilids seemed to be equally affected by the mycotoxins used in this study, whereas two species showed toxin-specific changes in survival. Only two (Kojic acid and Ochratoxin A) out of seven mycotoxins caused insect-specific responses. Moreover, we discovered correlations between survival in toxin-free and spoiled substrates, which may indicate an interrelationship between intra-specific competitive ability and resistance to mycotoxins. We discuss the significance of mycotoxins as underlying mechanisms driving competitive insect–fungus interactions.     

葡萄花翅小卷蛾抗药性研究进展

葡萄花翅小卷蛾是葡萄上的重要害虫,具有多食性、多化性等生物学特点,抗逆能力极强。该虫起源于欧洲,现已入侵全球多个国家。葡萄花翅小卷蛾主要以幼虫取食葡萄花序、幼果和成熟果实,给葡萄生产造成重大损失;其危害有利于真菌的侵入,导致灰霉病、白粉病等病害大量发生,从而造成葡萄腐烂。由于该虫入侵风险极高,已被我国列为重要的进境检疫性有害生物。国外对葡萄花翅小卷蛾的防治主要采用化学杀虫剂,由于长期大量且不合理地使用化学杀虫剂,葡萄花翅小卷蛾已对多种不同类型的杀虫剂产生了抗药性。本研究总结了葡萄花翅小卷蛾的抗性测定方法、抗性现状及其抗性机理,同时结合国外葡萄花翅小卷蛾抗性和防治相关研究,提出该虫抗性治理策略,并对我国预防该虫的入侵提出建议。     

Exposure to natural pathogens reveals costly aphid response to fungi but not bacteria

Immune responses are costly, causing trade‐offs between defense and other host life history traits. Aphids present a special system to explore the costs associated with immune activation since they are missing several humoral and cellular mechanisms thought important for microbial resistance, and it is unknown whether they have alternative, novel immune responses to deal with microbial threat. Here we expose pea aphids to an array of heat‐killed natural pathogens, which should stimulate immune responses without pathogen virulence, and measure changes in life‐history traits. We find significant reduction in lifetime fecundity upon exposure to two fungal pathogens, but not to two bacterial pathogens. This finding complements recent genomic and immunological studies indicating that pea aphids are missing mechanisms important for bacterial resistance, which may have important implications for how aphids interact with their beneficial bacterial symbionts. In general, recent exploration of the immune systems of non‐model invertebrates has called into question the generality of our current picture of insect immunity. Our data highlight that taking an ecological approach and measuring life‐history traits to a broad array of pathogens provides valuable information that can complement traditional approaches.     

Current status of the management of fall webworm,Hyphantria cunea: Towards the integrated pest management development

The fall‐webworm (FWW), Hyphantria cunea, is a highly polyphagous insect pest that is native to North America and distributed in different countries around the world. To manage this insect pest, various control methods have been independently evaluated in the invaded areas. Some of the control methods have been limited to the laboratory and need further study to verify their effectiveness in the field. On the other hand, currently, integrated pest management (IPM) has become a promising ecofriendly insect pest management option to reduce the adverse effect of insecticides on the environment. The development of an IPM for an insect pest must combine different management options in a compatible and applicable manner. In the native areas of the insect pests, there are some recommended management options. However, to date, there is no IPM for the management of the FWW in the newly invaded areas. Therefore, to develop an IPM for this insect pest, compilation of effective management option information is the first step. Thus, believing in the contribution of an IPM to the established management strategies, the chemical, biological, natural enemy, sex pheromone, and molecular studies regarding this insect were reviewed and potential future research areas were delineated in this review study. Therefore, using the currently existing management options, IPM development for this insect pest should be the subject of future research in the newly invaded areas.     

德国小蠊抗药性机理

德国小蠊(Blattella germanica)是一种重要的室内卫生害虫,化学防治是目前主要的防治手段,但抗药性已逐渐成为制约德国小蠊防治的关键因素。德国小蠊抗药性的产生存在多种机理,本文从行为抗性、表皮穿透性降低、代谢抗性、靶标抗性及微生物降解等方面对德国小蠊抗药性产生机理进行了综述,重点阐述了近年来德国小蠊抗药性机理最新的研究进展。     

Capturing the interaction types of two Bt toxins Cry1Ac and Cry2Ab on suppressing the cotton bollworm by using multi‐exponential equations

Transgenic crops are increasingly promoted for their practical effects on suppressing certain insect pests, but all transgenic crops are not equally successful. The insect pests can easily develop resistance against single Bacillus thuringiensis (Bt) toxin transgenic crops. Therefore, transgenic crops including two or more mixed Bt‐toxins can solve this problem by delaying the resistance development and killing the majority of targeted pests before the evolution of resistance. It is important to test the controlling effects of transgenic crops including multiple mixed toxins on a particular insect pest. Previous research has checked the cross‐resistance and interactions between Bt toxins Cry1Ac and Cry2Ab against one susceptible and four resistant strains of cotton bollworm. The results showed that independence was the main interaction type between two toxins for the susceptible strain, whereas synergism was the main interaction type for any one resistant strain. However, the optimal combinations of two toxins were not obtained. In the present study, we developed two multi‐exponential equations (namely bi‐ and tri‐exponential equations) to describe the combination effects of two Bt toxins. Importantly, the equations can provide predictions of combination effects of different continuous concentrations of two toxins. We compared these two multi‐exponential equations with the generalized linear model (GLM) in describing the combination effects, and found that the bi‐ and tri‐exponential equations are better than GLM. Moreover, the bi‐exponential equation can also provide the optimal dose combinations for two toxins.     

Proteomics as a tool for tapping potential of entomopathogens as microbial insecticides

Biopesticides are collective pest control harnessing the knowledge of the target pest and its natural enemies that minimize the risks of synthetic pesticides. A subset of biopesticides; bioinsecticides, are specifically used in controlling insect pests. Entomopathogens (EPMs) are micro‐organisms sought after as subject for bioinsecticide development. However, lack of understanding of EPM mechanism of toxicity and pathogenicity slowed the progress of bioinsecticide development. Proteomics is a useful tool in elucidating the interaction of entomopathogenic fungi, entomopathogenic bacteria, and entomopathogenic virus with their target host. Collectively, proteomics shed light onto insect host response to EPM infection, mechanism of action of EPM’s toxic proteins and secondary metabolites besides characterizing secreted and membrane‐bound proteins of EPM that more precisely describe relevant proteins for host recognition and mediating pathogenesis. However, proteomics requires optimized protein extraction methods to maximize the number of proteins for analysis and availability of organism's genome for a more precise protein identification.     

转Bt基因抗虫棉的生态风险及治理对策

评述了转Bt基因抗虫棉的生态风险及治理对策。其生态风险主要表现在目标害虫的抗性和对非目标生物群落的变化。目标害虫与转基因抗虫棉的互相作用和抗虫棉杀虫毒素的时空表达方式是目标害虫抗性发展的主要途径。在转基因抗虫棉田中,虽然对目标害虫的防治次数大为减少,但害虫和天敌群落的稳定性仍不如常规棉田,某种次要害虫大发生的可能性较大。认为将转基因抗虫棉纳入综合防治体系并培育更加高效的抗虫棉是治理目标害虫抗性和防止次要害虫上升的重要措施。     

Myths, models and mitigation of resistance to pesticides

Resistance to pesticides in arthropod pests is a significant economic, ecological and public health problem. Although extensive research has been conducted on diverse aspects of pesticide resistance and we have learned a great deal during the past 50 years, to some degree the discussion about ''resistance management'' has been based on ''myths''. One myth involves the belief that we can manage resistance. I will maintain that we can only attempt to mitigate resistance because resistance is a natural evolutionary response to environmental stresses. As such, resistance will remain an ongoing dilemma in pest management and we can only delay the onset of resistance to pesticides. ''Resistance management'' models and tactics have been much discussed but have been tested and deployed in practical pest management programmes with only limited success. Yet the myth persists that better models will provide a ''solution'' to the problem. The reality is that success in using mitigation models is limited because these models are applied to inappropriate situations in which the critical genetic, ecological, biological or logistic assumptions cannot be met. It is difficult to predict in advance which model is appropriate to a particular situation; if the model assumptions cannot be met, applying the model sometimes can increase the rate of resistance development rather than slow it down. Are there any solutions? I believe we already have one. Unfortunately, it is not a simple or easy one to deploy. It involves employing effective agronomic practices to develop and maintain a healthy crop, monitoring pest densities, evaluating economic injury levels so that pesticides are applied only when necessary, deploying and conserving biological control agents, using host-plant resistance, cultural controls of the pest, biorational pest controls, and genetic control methods. As a part of a truly multi-tactic strategy, it is crucial to evaluate the effect of pesticides on natural enemies in order to preserve them in the cropping system. Sometimes, pesticide-resistant natural enemies are effective components of this resistance mitigation programme. Another name for this resistance mitigation model is integrated pest management (IPM). This complex model was outlined in some detail nearly 40 years ago by V. M. Stern and colleagues. To deploy the IPM resistance mitigation model, we must admit that pest management and resistance mitigation programmes are not sustainable if based on a single-tactic strategy. Delaying resistance, whether to traditional pesticides or to transgenic plants containing toxin genes from Bacillus thuringiensis, will require that we develop multi-tactic pest management programmes that incorporate all appropriate pest management approaches. Because pesticides are limited resources, and their loss can result in significant social and economic costs, they should be reserved for situations where they are truly needed--as tools to subdue an unexpected pest population outbreak. Effective multi-tactic IPM programmes delay resistance (= mitigation) because the number and rates of pesticide applications will be reduced.