natural-products-in-plant-pest-management

Allelochemicals in Pest Management 145avoiding damage to non-target organisms so the potential value is great. Infact, insect damage to plants results from feeding or from transmission ofpathogens during feeding; therefore, the chemicals that reduce pest injury byrendering plants unattractive or unpalatable can be considered as potentialsubstitutes for conventional insecticides. The host choice of generalists andto some extent specialists may be modified when feeding inhibitors are used.The range of insect species targeted may be chosen by either the chemicalstructure of the inhibitor or the composition of a mixture of inhibitors, if differentinhibitors are active against different species within the range. Therefore,a multi-component defence strategy of plants themselves could be used,as shown in number of recent studies with non-azadirachtin types of limonoidinhibitors (Koul, 2005) where non-azadirachtin limonoids have two differentmodes of action, such as feeding deterrence and physiological toxicity, whichplay a significant role in the potentiation effect. Moreover some other plantextracts have high potential in commercial application (Pavela, 2007b).For the research to be successful, further assays must be performed andsuitable, new substances with high antifeedant efficiency must be sought.Important research will also concern determining synergism of the effects ofbiologically active substances as such synergism seems to be very significantin increasing the biological activity of substances that have insecticide effects(Pavela, 2008b).Most feeding inhibitors are less stable chemicals than traditional insecticidesand act with lower residual activity and environmental impact. Naturalpredators and parasitoids remain unharmed by feeding deterrents targetingthe herbaceous host insects. As the target sites of antifeedants are different,pesticide-resistant insect populations will still be affected by feeding inhibitors.Multi-component tactics will also slow down the resistance developmentto these new compounds. In fact, lack of resistance is very useful for thepractical application of antifeedants as it is unlikely that oligophagous insectscould develop general resistance to such deterrents, because this wouldresult in a rapid change of their host-plant range, which is determined mainlyby the occurrence of such chemicals in the non-host plants. Different molecularstructures of possible antifeedant compounds could be another advantage.The blend of active constituents might diffuse the selection process,mitigating the development of resistance compared to that expected with asingle active ingredient. This also supports the earlier mentioned contentionthat combination mixtures of antifeedants could be more effective thanindividual compounds.The huge variety of defensive mechanisms of plants, including thesynthesis of allelochemicals, thus provides a research focus in seeking newenvironmentally safe products to provide plant protection against phytophagousinsects. However, such research should be intensified and needsfull cooperation between basic or applied research, manufacturers and theusers. Such cooperation may lead subsequently to an important reduction inthe dependence of agriculture on chemical industries synthesizing toxicinsecticides, as well as increasing the quantity of safe foodstuffs and improvingthe health of this planet’s inhabitants.