Content uploaded by Zeshan Hassan
Author content
All content in this area was uploaded by Zeshan Hassan on Jan 21, 2019
Content may be subject to copyright.
A preview of the PDF is not available
Evaluation of venom peptides of two jumping spider species (Araneae: Salticidae) for use as insecticide potential
Abstract
Protein fractions in crude venom preparation of two species of the jumping spiders, Plexippus paykulli (Audouin) and Theyne imperialis (Rossi), were evaluated in the laboratory for their effectiveness against field-collected live Rhopalosiphum erysimi (Hemiptera: Aphididae). Venom glands of spiders were removed, and protein fractions from the venom were separated by SDS-PAGE. A common and dominant protein fraction (~29 kDa) in venom of each spider was selected for bioassay. The observed mortality rate of R. erysimi was 79.5% and 90% respectively against the tested protein fractions of P. paykulli and T. imperialis. Based on the results, it is concluded that selected protein fractions of P. paykulli and T. imperialis have bio-insecticide potential.
With a changing climate and cultivation of vast agricultural monocultures, the abundance of various pests shows an increase and their activity is shifting, expanding and intensifying. To avoid losses on crops, a variety of synthetic pesticides are increasingly being used to control harmful pests. This trend leads to overuse of pesticides, which has environmental consequences because these toxic chemicals enter the soil and water, can exhibit toxic effects on non-target organisms and could also eventually enter the food chain resulting in adverse impact on human health. Consequently, rapid development of nanotechnologies enabled the reformulation of pesticides into nanosystems, characterized by controlled release, targeted distribution, increased efficiency and reduced dose-dependent toxicity. In addition, so-called biopesticides, i.e. pesticides based on natural compounds, are toxic to specific pests and relatively harmless to non-target organisms and the ecosystem and could be easily formulated also in various types of nanoscale preparations.
This chapter gives a comprehensive overview of recent findings related to the activity and mechanisms of action of biopesticides including plant extracts and essential oils or their constituents, biopesticides produced by microorganisms, peptides obtained in spider venoms and Cry proteins produced by Bacillus thuringiensis in their bulk as well as nanoscale form against noxious weeds and harmful arthropods causing losses of economically important crops. Special attention is paid also to insecticidal activity of green synthesized metal nanoparticles against mosquitoes which are important vectors of many diseases causing annually more than a million deaths in tropical regions.
Keywords: arthropods, biopesticides, essential oils, bioherbicides, bioinsecticides, metals/metal oxides, microbial pesticides, nanoformulations, toxins, weeds
Lectins constitute a complex group of proteins found in different organisms. These proteins constitute an important field for research, as their structural diversity and affinity for several carbohydrates makes them suitable for numerous biological applications. This review addresses the classification and insecticidal activities of plant lectins, providing an overview of the applicability of these proteins in crop protection. The likely target sites in insect tissues, the mode of action of these proteins, as well as the use of lectins as biotechnological tools for pest control are also described. The use of initial bioassays employing artificial diets has led to the most recent advances in this field, such as plant breeding and the construction of fusion proteins, using lectins for targeting the delivery of toxins and to potentiate expected insecticide effects. Based on the data presented, we emphasize the contribution that plant lectins may make as tools for the development of integrated insect pest control strategies.
Over 10,000 arthropod species are currently considered to be pest organisms. They are estimated to contribute to the destruction of ~14% of the world's annual crop production and transmit many pathogens. Presently, arthropod pests of agricultural and health significance are controlled predominantly through the use of chemical insecticides. Unfortunately, the widespread use of these agrochemicals has resulted in genetic selection pressure that has led to the development of insecticide-resistant arthropods, as well as concerns over human health and the environment. Bioinsecticides represent a new generation of insecticides that utilise organisms or their derivatives (e.g., transgenic plants, recombinant baculoviruses, toxin-fusion proteins and peptidomimetics) and show promise as environmentally-friendly alternatives to conventional agrochemicals. Spider-venom peptides are now being investigated as potential sources of bioinsecticides. With an estimated 100,000 species, spiders are one of the most successful arthropod predators. Their venom has proven to be a rich source of hyperstable insecticidal mini-proteins that cause insect paralysis or lethality through the modulation of ion channels, receptors and enzymes. Many newly characterized insecticidal spider toxins target novel sites in insects. Here we review the structure and pharmacology of these toxins and discuss the potential of this vast peptide library for the discovery of novel bioinsecticides.
Biopesticides based on living microbes and their bioactive compounds have been researched and promoted as replacements for synthetic pesticides for many years. However, lack of efficacy, inconsistent field performance and high cost have generally relegated them to niche products. Recently, technological advances and major changes in the external environment have positively altered the outlook for biopesticides. Significant increases in market penetration have been made, but biopesticides still only make up a small percentage of pest control products. Progress in the areas of activity spectra, delivery options, persistence of effect and implementation have contributed to the increasing use of biopesticides, but technologies that are truly transformational and result in significant uptake are still lacking.
Venomous animals use their venoms as tools for defense or predation. These venoms are complex mixtures, mainly enriched of proteic toxins or peptides with several, and different, biological activities. In general, spider venom is rich in biologically active molecules that are useful in experimental protocols for pharmacology, biochemistry, cell biology and immunology, as well as putative tools for biotechnology and industries. Spider venoms have recently garnered much attention from several research groups worldwide. Brown spider (Loxosceles genus) venom is enriched in low molecular mass proteins (5-40 kDa). Although their venom is produced in minute volumes (a few microliters), and contain only tens of micrograms of protein, the use of techniques based on molecular biology and proteomic analysis has afforded rational projects in the area and permitted the discovery and identification of a great number of novel toxins. The brown spider phospholipase-D family is undoubtedly the most investigated and characterized, although other important toxins, such as low molecular mass insecticidal peptides, metalloproteases and hyaluronidases have also been identified and featured in literature. The molecular pathways of the action of these toxins have been reported and brought new insights in the field of biotechnology. Herein, we shall see how recent reports describing discoveries in the area of brown spider venom have expanded biotechnological uses of molecules identified in these venoms, with special emphasis on the construction of a cDNA library for venom glands, transcriptome analysis, proteomic projects, recombinant expression of different proteic toxins, and finally structural descriptions based on crystallography of toxins.
Pesticides are widely used in agricultural production to prevent or control pests, diseases, weeds, and other plant pathogens in an effort to reduce or eliminate yield losses and maintain high product quality. Although pesticides are developed through very strict regulation processes to function with reasonable certainty and minimal impact on human health and the environment, serious concerns have been raised about health risks resulting from occupational exposure and from residues in food and drinking water. Occupational exposure to pesticides often occurs in the case of agricultural workers in open fields and greenhouses, workers in the pesticide industry, and exterminators of house pests. Exposure of the general population to pesticides occurs primarily through eating food and drinking water contaminated with pesticide residues, whereas substantial exposure can also occur in or around the home. Regarding the adverse effects on the environment (water, soil and air contamination from leaching, runoff, and spray drift, as well as the detrimental effects on wildlife, fish, plants, and other non-target organisms), many of these effects depend on the toxicity of the pesticide, the measures taken during its application, the dosage applied, the adsorption on soil colloids, the weather conditions prevailing after application, and how long the pesticide persists in the environment. Therefore, the risk assessment of the impact of pesticides either on human health or on the environment is not an easy and particularly accurate process because of differences in the periods and levels of exposure, the types of pesticides used (regarding toxicity and persistence), and the environmental characteristics of the areas where pesticides are usually applied. Also, the number of the criteria used and the method of their implementation to assess the adverse effects of pesticides on human health could affect risk assessment and would possibly affect the characterization of the already approved pesticides and the approval of the new compounds in the near future. Thus, new tools or techniques with greater reliability than those already existing are needed to predict the potential hazards of pesticides and thus contribute to reduction of the adverse effects on human health and the environment. On the other hand, the implementation of alternative cropping systems that are less dependent on pesticides, the development of new pesticides with novel modes of action and improved safety profiles, and the improvement of the already used pesticide formulations towards safer formulations (e.g., microcapsule suspensions) could reduce the adverse effects of farming and particularly the toxic effects of pesticides. In addition, the use of appropriate and well-maintained spraying equipment along with taking all precautions that are required in all stages of pesticide handling could minimize human exposure to pesticides and their potential adverse effects on the environment.
Modern agricultural systems during the last 50–60 years have largely followed ‘substitution agriculture’, in which weed, pest, and disease control is usually achieved by agrichemical use that has caused severe environmental harm, including reductions in biodiversity. This type of agriculture is increasingly becoming be unsustainable. Pressure for sustainable practices, both through markets and regulatory bodies, and the increasing problem of pesticide resistance are pushing the industry to find alternatives to agrichemicals. Currently, such alternatives include plant-derived essential oils, plant defense stimulants, biopesticides, and conservation biological control techniques. At this time, conservation biological control and biopesticides are being used in narrow niches of agriculture and are generally effective with an understanding of the system and its limitations. Research is now underway to make both these techniques more effective under a wider range of environmental conditions, pest species, and cropping systems.
Ralf Nauen and Thomas Bretschneider of Bayer CropScience AG, Research, based at Monheim in Germany outline the development of new insecticides based on novel modes of action.
Biopesticides are very effective in the agricultural pest control without causing serious harm to ecological chain or worsening environmental pollution. The research and development of practical applications in the field of biopesticides greatly mitigate environmental pollution caused by chemical pesticide residues and promotes sustainable development of agriculture. Since the advent of biopesticides, a large number of products have been released, several of which have already played dominant roles in the market. The development of biopesticides stimulates modernization of agriculture and will, without doubt, gradually replace chemical pesticides. Many biopesticides are ideal substitutes for their traditional chemical counterparts in pollution-free agricultural production, but some of them display certain toxicity; this should be taken into consideration by the researchers in the field. In this paper, we discuss the current development and application of biopesticides from various categories, the problems occurring in the process of their development and proposing the introduction of various constraints. We review various studies and analyze the development trends in biopesticides in agriculture, demand, market and other fields.
Previously, we have described the properties of recombinant baculoviruses expressing three chimeric genes,mag4, sat2,andssh1,that encode secretable insect selective sodium channel toxins, μ-Aga-IV from the spiderAgelenopsis aperta,As II from the sea anemoneAnemonia sulcata,and Sh I from the sea anemoneStichadactyla helianthus,respectively. We now show that μ-Aga-IV and As II act at distinct sites on voltage-sensitive sodium channels of insects and synergistically promote channel opening. We also show that these toxins have synergistic insecticidal activity against the blowflyLucilia sericataand the fall armywormSpodoptera frugiperda.To determine if toxin synergy also occurs in the context of virus replication, we inserted the chimeric toxin genes into nonessential sites of theAutographa californicanuclear polyhedrosis virus (AcMNPV) genome under the control of either a modified promoter, PsynXIV, or an insect derived promoter, Phsp70. Comparative analyses showed that viruses expressing toxin genes under the control of the Phsp70promoter were more effective as biopesticides than under the control of PsynXIV. Two toxins, μ-Aga-IV and As II, exerted the most potent effects inS. frugiperdaandTrichoplusia nilarvae, respectively. A virus simultaneously expressing two Phsp70-promoted toxin genes,mag4andsat2,exhibited properties similar to the two viruses expressing each of the toxin genes individually except that larval feeding time (FT50) was reduced an additional 10%, indicating a small advantage to coproducing synergistic toxins.
Molecular toxinology research was initially driven by an interest in the small subset of animal toxins that are lethal to humans. However, the realization that many venomous creatures possess a complex repertoire of bioactive peptide toxins with potential pharmaceutical and agrochemical applications has led to an explosion in the number of new peptide toxins being discovered and characterized. Unfortunately, this increased awareness of peptide-toxin diversity has not been matched by the development of a generic nomenclature that enables these toxins to be rationally classified, catalogued, and compared. In this article, we introduce a rational nomenclature that can be applied to the naming of peptide toxins from spiders and other venomous animals.