Efficacy of certain common ferns against red spider mite Oligonychus coffeae and tea mosquito bug Helopeltis theivora infesting tea

Abstract

In search for botanicals as an alternative remedy to synthetic chemicals in the pest control of tea plantations, ferns such as Adiantum raddianum, Asplenium aethiopicum, Cyclosorus interruptus, Dicranopteris linearis, Diplazium polypodioides, and Pteridium aquilinum were evaluated against the two major pests of tea, red spider mite Oligonychus coffeae Nietner and tea mosquito bug Helopeltis theivora Waterhouse, which are the foremost seasonal pests in tea fields, causing severe crop loss. Apart from synthetic chemicals, only the neem kernel extract is recommended in tea fields. The aqueous extracts of ferns were screened at different concentrations against these pests under laboratory and field conditions. The extracts of P. aquilinum and D. linearis showed good contact toxicity at a 5% concentration to O. coffeae. The acaricidal activity was observed in the order P. aquilinum > D. linearis > C. interruptus > A. raddianum > D. polypodioides > A. aethiopicum. Under field conditions, the extract of D. linearis and P. aquilinum showed a 50% reduction in the population of red spider mite and caused no phytotoxic effect to tea leaves. But their insecticidal activity was less pronounced against H. theivora. They exhibit antifeedant activity, which was sustained only for 24 hours. The photochemical screening of extracts showed a qualitatively increased level of saponins in P. aquilinum, D. linearis, and C. interruptus. The study shows that the aqueous extracts of D. linearis and P. aquilinum can be incorporated in the mite control programme in tea.