Can microbial-based insecticides replace chemical pesticides in agricultural production?

Extensive use of chemical insecticides to control insect pests in agriculture has improved yields and production of high-quality food products. However, chemical insecticides have been shown to be harmful also to beneficial insects and many other organisms like vertebrates. Thus, there is a need to replace those chemical insecticides by other control methods in order to protect the environment. Insect pest pathogens, like bacteria, viruses or fungi, are interesting alternatives for production of microbial-based insecticides to replace the use of chemical products in agriculture. Organic farming, which does not use chemical pesticides for pest control, relies on integrated pest management techniques and in the use of microbial-based insecticides for pest control. Microbial-based insecticides require precise formulation and extensive monitoring of insect pests, since they are highly specific for certain insect pests and in general are more effective for larval young instars. Here, we analyse the possibility of using microbial-based insecticides to replace chemical pesticides in agricultural production.     

Exotic Lepidopteran Leafminers in North American Apple Orchards: Rise to Prominence, Management, and Future Threats

The European tentiform leafminers, Phyllonorycter blancardella (Fabricius) and P. mespilella (Hübner) (Lepidoptera: Gracillariidae), have infested apple, Malus domestica Borkhausen, in North America for at least 60–70 years. Unreliable taxonomic methods and lack of voucher specimens, however, have contributed to poor understanding of precisely when, where, and how these leafminers were introduced. Tentiform leafminers developed into significant foliar pests at about the time when adult resistance to broad-spectrum insecticides was detected in the 1970s and 1980s. At present, growers manage leafminers with insecticides and, to a lesser extent, with biological control. Most management programs for orchard pests rely on insecticides that are highly toxic to parasitic wasps, which hampers biological control. New techniques promoted in the context of integrated pest management (IPM) may improve biological control by reducing insecticidal use, but their adoption will depend on cost, labor, need to control other pests, and demands of the marketplace. Management programs must be flexible enough to accommodate changes in the species composition of leafminers and their parasitoids. Procedures to exclude pests may slow the rate of new introductions of leafminers and other pests, but they will not entirely protect the North American apple industry. Once new apple pests reach North America, they face few obstacles to further dispersal. The abundance of potential host plants, the lack of rigorous inspections, and new retail practices may facilitate the dispersal of exotic pests.     

Extracellular hydrolytic enzymes produced by entomopathogenic fungi--role in an infection process

Entomopathogenic fungi have a great potential in biological control of insect pest population. Fungal pathogens are promising source of insecticides and notable alterative to chemical pesticides. These fungi possess a unique mechanism of insects paralysis. As natural enemies of insects they attack direct host cuticle via a combination of mechanical pressure and cuticle-degrading enzymes. Entomopathogenic fungi produce several proteo-, chitino- and lipolytic enzymes, which are accepted as key factors in insect mycosis. The role of extracellular enzymes in pathogenesis is still not well understood. Profound understanding the mechanisms of insect paralysis by entomopathogenic fungi will help in the production of safer for environment and more efficiency mycoinsecticides.     

Correlation of fruit tree rhizosphere soils with entomopathogenic fungi

Entomopathogenic fungi are microorganisms that control the density of host insects in nature; they are being studied as environmentally friendly alternatives to chemical insecticides for controlling insect pests. The main habitat of entomopathogenic fungi is soil, and the correlation between the distribution of entomopathogenic fungi and the physicochemical characteristics of soils planted with different trees, including vine (outdoor, greenhouse, and greenhouse shine musket), apple, peach, and pear, were analyzed. The entomopathogenic fungi of the genera Beauveria, Metarhizium, and Purpureocillium investigated in this study were all found in soil samples from vine-greenhouse, apple, and peach trees. Purpureocillium and Beauveria abundances were positively correlated with soil properties; however, Metarhizium abundances were not correlated with soil properties. The Metarhizium isolates discovered in this study showed pathogenicity to cotton aphids (an agricultural pest) and can be employed as sources for biological studies in the future. This study provides data on the diversity and abundance of entomopathogenic fungi related with soil properties, as well as the molecular, biological, and insecticidal characteristics of Metarhizium isolates.     

Insect growth regulatory and larvicidal activity of chalcones against Aedes albopictus

Widespread use of chemical insecticides has resulted in development of insect resistance and natural products with biological activities could become an attractive alternative to control insect pests. In order to find more effective insecticides for controlling mosquito, various mosquitocidal compounds are studied. Recently, juvenile hormone antagonists (JHANs) have been found to be to safe and effective insecticides for control of mosquito. In order to identify novel insecticidal compounds with JHAN activity, several chalcones were surveyed on their JHAN activities and larvicidal activities against Aedes albopictus larvae. Among them, 2′‐hydroxychalcone and cardamonin showed high levels of JHAN and mosquito larvicidal activities. These results suggested that chalcones with JHAN activity could be useful for control of mosquito larvae.     

Tandem use of selective insecticides and natural enemies for effective,reduced-risk pest management

Selective chemical insecticides have become the dominant approach for management of recalcitrant and resistant insect pests, and the prospects for use of these chemicals in combination with biocontrol agents are on the rise. These chemical compounds, when used in combination with an effective natural enemy, may provide more comprehensive prophylactic and remedial treatments in the context of an integrated pest management program (IPM) than either approach alone. Many of these compounds have promise for a diversity of applications, including sustainable agriculture, control of urban pests, and invasive species eradication. Unfortunately, there are only a limited number of studies in which the effect of these insecticides on natural enemies has been examined. In this article, we examine the risk of several classes of insecticidal compounds to non-target animals, particularly natural enemies and pollinators, and review the most promising compounds for combined deployment with biological agents.     

Characteristics of insecticidal substances from the entomopathogenic fungus Metarhizium pinghaense 15R against cotton aphid in Korea

Aphids (Hemiptera: Aphididae) are agricultural pests for a wide range of economically important crops worldwide. Entomopathogenic fungi have been studied and developed as a biological agents to control hard to control insect pests like the aphid. In particular, secondary metabolites produced by entomopathogenic fungi are being studied as insecticidal substances. This study evaluated the insecticidal activity and characteristics of insecticidal substances in culture filtrate against aphids to confirm the insecticidal substances produced by Metarhizium pinghaense 15R. After treating cotton aphids with the culture filtrate, strong insecticidal activity (100 % insect mortality) was observed on the third day of treatment, and it was confirmed that insecticidal substances in the culture filtrate had high thermal stability. In addition, the physicochemical properties of insecticidal substances in the culture filtrate were evaluated, and it was determined that the insecticidal substances were hydrophobic, with small molecules of 3 kDa or less. Based on these results, it was suspected that the insecticidal substances in the culture filtrate were destruxins (DTXs), which are representative secondary metabolites of Metarhizium known to have insecticidal activity. Through HPLC (High Performance Liquid Chromatography) analysis, the presence of DTX A and B was found in all active samples, and it was confirmed that the insecticidal substances of M. pinghaense 15R were DTXs. This study provides primary data for developing biochemical crop protection agents using these insecticidal substances, and we suggest the potential of using insecticidal substances of entomopathogenic fungi as biochemical pesticides in Korea.     

Bacillus thuringiensis: a biotechnology model

This paper is on the different biotechnological approaches that have been used to improve Bacillus thuringiensis (Bt) for the control of agricultural insect pests and have contributed to the successful use of this biological control agent; it describes how a better knowledge of the high diversity of Bt strains and toxins genes together with the development of efficient host-vector systems has made it possible to overcome a number of the problems associated with Bt based insect control measures. First we present an overview of the biology of Bt and of the mode of action of its insecticidal toxins. We then describe some of the progress that has been made in furthering our knowledge of the genetics of Bt and of its insecticidal toxin genes and in the understanding of their regulation. The paper then deals with the use of recombinant DNA technology to develop new Bt strains for more effective pest control or to introduce the genes encoding partial-endotoxins directly into plants to produce insect-resistant trangenic plants. Several examples describing how biotechnology has been used to increase the production of insecticidal proteins in Bt or their persistence in the field by protecting them against UV degradation are presented and discussed. Finally, based on our knowledge of the mechanism of transposition of the Bt transposon Tn4430, we describe the construction of a new generation of recombinant strains of Bt, from which antibiotic resistance genes and other non-Bt DNA sequences were selectively eliminated, using a new generation of site-specific recombination vectors. In the future, continuing improvement of first generation products and research into new sources of resistance is essential to ensure the long-term control of insect pests. Chimeric toxins could also be produced so as to increase toxin activity or direct resistance towards a particular type of insect. The search for new insecticidal toxins, in Bt or other microorganisms, may also provide new weapons for the fight against insect damage.     

Entomopathogenic fungi and insect behaviour: from unsuspecting hosts to targeted vectors

The behavioural response of an insect to a fungal pathogen will have a direct effect on the efficacy of the fungus as a biological control agent. In this paper we describe two processes that have a significant effect on the interactions between insects and entomopathogenic fungi: (a) the ability of target insects to detect and avoid fungal pathogens and (b) the transmission of fungal pathogens between host insects. The behavioural interactions between insects and entomopathogenic fungi are described for a variety of fungal pathogens ranging from commercially available bio-pesticides to non-formulated naturally occurring pathogens. The artificial manipulation of insect behaviour using dissemination devices to contaminate insects with entomopathogenic fungi is then described. The implications of insect behaviour on the use of fungal pathogens as biological control agents are discussed.     

新型二酰胺类杀虫剂对鱼尼丁受体作用的分子机理

最近发现了一类新型二酰胺类杀虫剂——氟虫酰胺和氯虫酰胺,其作用靶标是鱼尼丁受体 (ryanodine receptors, RyRs)。本文对RyR的结构与功能、电压门控钙离子通道和鱼尼丁受体钙离子释放通道对细胞质钙离子内环境稳定的调节以及二酰胺类杀虫剂对RyRs作用的分子机理进行综述。二酰胺类杀虫剂使昆虫RyR通道处于持续的开放状态,引发钙离子从肌质网腔内大量释放,破坏了细胞质钙离子内环境的稳定,从而产生不同的药物学特性。这些变化都是由一个不同于鱼尼丁在RyR上的结合部位介导的。该类杀虫剂的作用对昆虫RyR s是高度专一的,结果产生选择毒性。由于二酰胺类杀虫剂的结构独特,作用方式新颖,对鳞翅目害虫效果好、杀虫谱广,对各种益虫和天敌安全,并对现用的杀虫剂无交互抗性,故它们非常适合于抗性治理和IPM。     

A review of <Emphasis Type="Italic">Piper</Emphasis> spp. (Piperaceae) phytochemistry,insecticidal activity and mode of action

The tropical plant family Piperaceae has provided many past and present civilizations with a source of diverse medicines and food grade spice. The secondary plant compounds that produce these desired qualities function also as chemical defenses for many species in the genus Piper. The compounds with the greatest insecticidal activity are the piperamides. Many studies have shown the effectiveness of Piper spp. extracts for the control of stored products pests and recently studies from our laboratory group have tested the extracts of Piper. nigrum, P. guineense and P. tuberculatum against insect pests of the home and garden. These results and those from investigations that examined the biochemical and molecular modes of action of the piperamides singly or in combination will be the focus of this review. The conclusions of our current work with Piperaceae are that Piper extracts offer a unique and useful source of biopesticide material for controlling small-scale insect out-breaks and reducing the likelihood of resistance development when applied as a synergist with other botanical insecticides such as pyrethrum.     

A review on the genus Metarhizium as an entomopathogenic microbial biocontrol agent with emphasis on its use and utility in Mexico

Metarhizium is a genus of entomopathogenic fungi that was initially classified into three species and varieties. More recently, DNA sequencing has improved the phylogenetic resolution of Metarhizium which now includes 30 species. The insect host ranges vary within the genus and some species such as M. robertsii have broad host ranges, while others such as M. acridum show a narrow host range and are restricted to the order Orthoptera. Metarhizium spp. are ubiquitous naturally occurring soil inhabiting fungi, and some are rhizosphere colonisers and their diversity has been attributed to various selective factors (habitat type, climatic conditions, specific associations with plants and insect hosts). Metarhizium have been used for the biological control of insect pests that affect economically important agricultural crops and have been tested under laboratory and field conditions for the control of insect vectors of human disease, showing the effectiveness of the fungus against the target pest. In Mexico, Metarhizium species have been used for the control of insect pests such as the spittlebug (Hemiptera: Cercopidae), and locusts (Orthoptera) that affect crops such as corn, bean and sugarcane. Biosafety studies, such as dermal and intragastric tests in mammalian models have also been carried out to ensure safety to humans and other animals. Metarhizium shows great promise as an alternative to chemical insecticides that has relatively low impact on human health and the environment. Key features of Metarhizium for biocontrol of insects are outlined with special reference to their utility in Mexico.     

New and selective ryanodine receptor activators for insect control

Diamide insecticides have emerged as one of the most promising new classes of insecticide chemistry owing to their excellent insecticidal efficacy and high margins of mammalian safety. Chlorantraniliprole and flubendiamide, the first two insecticides from this class, demonstrate exceptional activity across a broad range of pests in the order Lepidoptera. This chemistry has been confirmed to control insects via activation of ryanodine receptors which leads to uncontrolled calcium release in muscle. The high levels of mammalian safety are attributed to a strong selectivity for insect over mammalian receptors.     

重组病毒杀虫剂应用研究进展

应用分子生物学技术可以将昆虫特异性的毒素基因、某些酶基因等外源基因插入昆虫病毒基因组,或通过改造昆虫病毒基因组等方法构建重组病毒杀虫剂,提高杀虫效果。温室及田间释放实验证实,重组病毒杀虫剂可以显著提高现场防治效果。连续多代抗性筛选实验表明,宿主被诱导产生对重组病毒杀虫剂抗性的速度低于野生型病毒杀虫剂。采用在剂型中添加光增白剂等保护剂、在基因组中插入具有增效作用的基因、应用病毒增强蛋白等技术可以提高重组病毒杀虫效果。随着基因工程技术的发展和安全性研究的深入,以重组杆状病毒为主的重组昆虫病毒杀虫剂的应用研究正面临着突破。     

寄主植物影响害虫药剂敏感性的研究进展

害虫取食不同寄主植物后,对杀虫剂的反应可归为3类：敏感性降低、增高和无明显变化。害虫对药剂的敏感性变化与不同植物中次生物质诱导激活/抑制昆虫体内相关解毒酶活性有关。这种诱导作用可受到植物营养、次生物质种类及其含量分布、害虫种类与发育阶段、以及环境温度等多种因素影响。经诱导的昆虫解毒酶对不同类型杀虫剂的代谢能力并不相同,进而导致对不同药剂的敏感性变化有明显差异。解毒酶系的诱导激活在害虫抗药性形成早期被认为有利于提高隐性抗性基因频率,从而可促进害虫抗药性的发展。最后,就寄主植物影响害虫对药剂敏感性在害虫治理中的应用作了探讨。     

Can fungal biopesticides control malaria?

Recent research has raised the prospect of using insect fungal pathogens for the control of vector-borne diseases such as malaria. In the past, microbial control of insect pests in both medical and agricultural sectors has generally had limited success. We propose that it might now be possible to produce a cheap, safe and green tool for the control of malaria, which, in contrast to most chemical insecticides, will not eventually be rendered useless by evolution of resistance. Realizing this potential will require lateral thinking by biologists, technologists and development agencies.     

Lactic acid fermentation of potato pulp by the fungus Rhizopus oryzae

Production of molecules with toxic activity by genetically transformed symbiotic bacteria of pest insects may serve as a powerful approach to biological control. The symbiont, Enterobacter gergoviae, isolated from the gut of the pink bollworm (PBW), has been transformed to express Cyt1A, a cytolytic protein toxin lethal to mosquito and black fly larvae, as a model system. These transgenic bacteria might be used to spread genes encoding insecticidal proteins to populations of agricultural insects or as replacement for chemical insecticides such as malathion used in bait formulation to control specific insect pests, because of extreme public pressure against organophosphate pesticide spraying. Received: 27 November 2000 / Accepted: 29 December 2000     

Insecticidal activity of inhibitors of polyamine biosynthesis on Spodoptera litura F. larvae.

The inhibitors of polyamine (PA) biosynthesis such as alpha-difluoromethylornithine (DFMO), methylglyoxal bis (guanylhydrazone) (MGBG) and bis (cyclohexylammonium) sulphate (BCHA) have been used to protect crop plants from pathogenic fungi. In this communication the insecticidal activity of these inhibitors on tobacco caterpillar, S. litura has been reported. All the inhibitors exhibited insecticidal activity; MGBG being more effective than others. The results suggest, for the first time, a possible avenue for the control of insect pests by specific inhibition of insect PA biosynthesis.     

Integrated rice insect pest control in the Guangdong Province of China

There are about 13 species of rice insect pests which are common and of major significance in Guangdong Province, China. Rice pest management in China is based on cultural practices, biological control, insecticides, light traps, varietal resistance and other control methods. Natural control by preservation of natural enemies of pests plays a very positive role in the integrated control of rice pests. The major measures and techniques of these control methods are mentioned in this paper. A list of main insect pests of rice, their natural enemies and some examples of the results of rice pest integrated control in Guangdong Province, China, are also given.