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Mechanisms of insecticide resistance were studied in five rice insect pests (brown planthopper Nilaparvata lugens; green leafhopper Nephotettix virescens; paddy bug Leptocorisa oratorius; white leafhopper Cofana spectra and white- backed planthopper Sogatella furcifera), and four of their predators (ladybird beetle Micraspis discolor; ground beetle Ophionea indica; mired bug Cytorhinus lividipennis and spider Tetragnatha sp.). Insects were collected from the rice fields at Batalagoda, Kurunegala, during 2001 - 2003 and stored at -20°C Biochemical assays were carried out within one week of storage to determine the activity levels of major enzyme groups (i.e carboxylesterases, glutathione S-transferases and mono- oxygenases), which are involved in insecticide metabolism. Native polyacrylamide gels were run with crude homogenates to resolve carboxylesterase isozymes. Sensitivity of the organophosphate and carbamate target site acetylcholineesterase was tested by inhibiting the enzyme with propoxur. N. lugens, S. furcifera and N. virescens showed high insecticide resistance, especially to organophospha tes and pyrethroids due to higher activity levels of metabolic enzymes. All the species were susceptible to malathion mainly because of the absence of malathion carboxylesterase mechanism. Resistance to permethrin in the populations of N. lugens, C. lividipennis, M. discolour, O. indica and Tetragnatha sp. may be due to their higher mono-oxygenase activities. Presence of insensitive acetylcholinesterases could be detected among the populations of N.lugens, C. spectra, C. lividipennis and Tetragnatha sp. It appears that multiple resistance mechanisms are present in the populations tested. Higher susceptibility levels of L. oratorius and C. spectra could be attributed to the absence of resistance mechanisms in these two species.

journal of the national science foundation of sri lanka/journal of the national science foundation

Involvement of metabolic and insensitive acetylcholinesterase mechanisms in insecticide resistance of rice insect pests and predatory populations from Batalagoda, Sri Lanka