Phytochemicals for pest management

Abstract

Plants produce bioactive chemicals to cope with pathogens, competing plant species, and herbivorous insects and vertebrates. Accordingly, phytochemicals have been used directly or have been the inspiration for some important pesticide classes, such as the pyrethroid insecticides and triketone herbicides. This paper summarizes several examples of pesticide discoveries from plants made in our laboratory, as well as modern approaches for genetically altering or imparting production of pest-fighting phytochemicals in crops. A 9,10-anthraquinone derivative for use in aquaculture to selectively control undesirable blue-green algae was found to be more effective than algaecides currently used. Two norclerodanes from american beautyberry (Callicarpa Americana) were found to be potent insect repellents. Natural triketones from oil of manuka (Leptospermum scoparium) were discovered be good inhibitors of p-hydroxyphenylpyruvate dioxygenase and potential herbicides for organic farmers. Sampangine from the bark of the Cleistopholis patens tree was sufficiently fungitoxic to be patented as an agricultural fungicide. We found the sesquiterpenoid vulgarone B to be as active against two important snail pests as metaldehyde, one of the most commonly used molluscicides. Examples of termiticidal compounds from plant sources, such as apiol from Lomatium hultenii, will be discussed. Transgenic manipulation of the biosynthesis of sorgoleone, a natural herbicide produced by root hairs of Sorghum species, has been accomplished in our laboratory. These genetic tools extend the possibilities for using phytochemicals as pesticides in agriculture. Our experience has been that plants are rich sources of novel compounds that can be the bases for new pesticides or genetic approaches to plant protection.