Influence of chemical profiles of host plants on the infestation diversity of Retithrips syriacus.

ABSTRACT

The onset of biotic stress in the host plants as a result of increased insect population size leads to enhanced levels of secondary metabolites and associated phenolic enzyme activity· Of the three host plants examined, viz. Ricinus communis (castor), Eucalyptus globulus (eucalyptus) and Manihot utilissima (tapioca), castor was the host most preferred by Retithrips syriacus· Despite the fact that tapioca had the highest levels of secondary compounds, thrips infestation persisted· However, fecundity and growth were reduced because of the relatively high levels of primary metabolites. Gallic acid was found to be the most toxic of the phenolic acids, followed by pyrogallol, resorcinol, phloroglucinol and vanillic acid· The less toxic phenolic acids and flavanoids were detected in leaves that harboured thrips, while the preponderance of gallic acid was found in uninfested hosts. Thus the interaction of Retithrips syriacus with the hosts is governed essentially by the biochemical profiles of its hosts, which tend to be altered subsequent to infestation, thus manifesting induced resistance through enhanced production of phenolics.