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

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) andManihot utilissima (tapioca), castor was the host most preferred byRetithrips 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 ofRetithrips 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

Comparison of life cycle traits of a Helopeltis theivora Waterhouse (Heteroptera: Miridae) population infesting organic and conventional tea plantations, with emphasis on deltamethrin resistance

The tea mosquito bug, Helopeltis theivora (Waterhouse), is an important economic pest of tea in India. The development of resistance in H. theivora populations obtained from a conventional plantation as compared with a strain from an organic plantation was studied in the laboratory for five generations, and associated changes in life cycle traits were assessed. Selection using sublethal concentrations of deltamethrin resulted in a 5.19-fold increase in insecticide resistance ratio from the F1 to the F5 generation in the H. theivora population from the conventional plantation. By the F5 generation, nymphal duration and total developmental duration and adult longevity were higher and fecundity was lower in the deltamethrin-selected strain than in the non-selected strain from a conventional plantation and the susceptible strain from an organic plantation. These findings have practical implications for insecticide resistance management of this important sucking pest of tea