natural-products-in-plant-pest-management

Allelochemicals in Pest Management 137of products (Pavela and Herda, 2007a,b). Moreover, their antifeedant efficiencyis often connected with further biological activity such as growth inhibitionand cumulative mortality.Allomones with antifeedant activity include a high percentage ofsubstances that also meet the following requirements for development ofnew botanical insecticides:●●●●They are natural plant metabolites, safe for health and the environment;Such substances provide specific effects on individual pest species – theythus show high selectivity;Mixtures of substances with synergistic effects can be obtained, whichprevent the development of pest resistance;Antifeedant substances usually show other biological effects such asgrowth inhibition, mortality and reduced fertility of surviving individuals,which increase the practical efficiency of the products (Isman, 2002;Koul, 2005).All these characteristics increase the prospects for the use of antifeedantsubstances in plant protection. However, products based on allomonesshould be applied as a preventative measure, for example, at the time of pestinvasion or its initial occurrence or at the time of larval incubation. Althougha large number of biologically active substances and extracts from plantswith antifeedant effects have been tested, only a limited number of productshave been subjected to a detailed field application and in the development ofplant protection products (Isman, 1994).6.3 Current State of Antifeedant ResearchThe history of the research of substances that show antifeedant effects datesback to the 1930s. As early as 1932, Metzger and Grant tested about 500 plantextracts against Popilla japonica, although results were not substantiallyencouraging. Later, Pradhan et al. (1962) evaluated extracts of the Indianneem tree, Azadirachta indica, that prevented feeding by the desert locusts.Although terrestrial plants produce a diverse array of secondary metabolites,probably more than 100,000 unique compounds (Isman, 2002), today, about900 compounds have been identified to possess feeding deterrence againstinsects (Koul, 2005).In addition to various compounds isolated from plants or synthesized asinsect antifeedants, several studies demonstrate the antifeedant efficacy inmetabolite mixtures of plant essential oils or total extracts against a variety ofinsect species.In recent years studies have revealed the antifeedant potential of plantessential oils against postharvest pests, aphids, thrips, lepidopterans, termitesand mite pests (Hori, 1999; Hou-HouaMin et al., 2002; Koul, 2005;Isman, 2006). Similarly, during the past few years much emphasis has beenplaced on demonstrating the antifeedant efficacy in total plant extracts(Mancebo et al., 2000a,b; Wang et al., 2000; Pavela, 2004a,b; Zhang et al., 2004;