Evaluation of some indigenous plant extracts against red spider mite, Oligonychus coffeae Nietner (Acari: Tetranychydae) in tea

An experiment was conducted to evaluate the toxicity of some locally available indigenous plants such as Bishkatali (Polygonum hydropiper), Burweed (Xanthium strumarium), Datura (Datura metel), Lantana (Lantana camara), Mahogani (Swietenia mahagoni) and Neem (Azadirachta indica) at 2.5, 5.0 and 10.0% (w/v) concentrations against red spider mite, Oligonychus coffeae under both laboratory and field conditions at Bangladesh Tea Research Institute, Srimangal, Moulvibazar during 2012–2013. Effect of plant extracts on mortality of two natural predators of Stethorus gilvifrons (Coccinellidae) and Oxyopes sp. (Oxyopidae) and quality of made tea by organoleptic test were also studied. Data were collected at 24 HAT (Hours After Treatment), 48 HAT, 72 HAT in the laboratory and at weekly interval in field condition. Results revealed that aqueous extract of X. strumarium showed the highest average mortality (89.66%) of red spider mite at 10% concentration after 72 HAT followed by S. mahagoni (86.21%) whereas aqueous extracts of P. hydropiper, D. metel, L. camara and A. indica exhibited pronounced acaricidal action (69.94–81.24%) at 72 HAT at the same concentration. Similar trend of toxicity was also observed at 24 HAT and 48 HAT. From the field evaluation it was found that the highest (82.27–83.72%) reduction in mite population was observed at 10% concentrations of X. strumarium followed by S. mahagoni (79.47– 80.94%). The order of toxicity of the tested aqueous plant extracts on adult red spider mite was: X. strumarium S. mahagoni P. hydropiper L. camara A. indica D. metel in both laboratory and field conditions. Application of the tested biopesticides did not affect the natural predators such as Stethorus gilvifrons and Oxyopes sp. at 10% of concentration. Made tea produced from plant extracts treated shoots were found above average quality and taint free when subjected to organoleptic evaluation. These indigenous plants can therefore be incorporated in the integrated pest management (IPM) strategy of red spider mite and reduce the load of synthetic chemicals in tea ecosystem.