Decrease of rice plant resistance and induction of hormesis and carboxylesterase titre in brown planthopper, Nilaparvata lugens (Stål) by xenobiotics

The brown planthopper (BPH), Nilaparvata lugens (Stål) is a serious threat to the rice production throughout Asia. The indiscriminate application of various xenobiotics in rice ecosystem is perceived as one of the factors for the frequent outbreak of BPH. The present study has critically analysed the secondary effects of some xenobiotics used in rice field on certain plant and insect parameters that subsequently favour BPH outbreak. Application of 2,4-D, carbendazim, deltamethrin and urea reduced the innate BPH resistance of PTB 33 rice variety due to favourable alterations in rice free amino acid and sucrose content. Similarly, these chemicals also induced hormesis and enhanced feeding in BPH. Alternatively, soil amendment with neem seed powder and Calotropis gigantea leaves improved plant innate resistance and showed no sign of hormesis or enhanced feeding in BPH. In addition, deltamethrin has the ability to stimulate BPH carboxylesterase titre. Native PAGE analysis of esterases from whole body homogenate of BPH revealed at least five esterase isozyme bands, prominent being E1 and E2. However, no difference in BPH esterase banding pattern was observed between different xenobiotic treatments. All these esterase bands are classified under carboxylesterase based on their inhibition by class specific esterase inhibitors.

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► Application of xenobiotics in rice ecosystem has certain adverse secondary effects.
► Decreases the innate resistance of rice against insect pests.
► Causes hormesis and increased feeding in BPH; Enhances BPH carboxylesterase activity.
► Soil amendment with botanicals increases the innate plant resistance and suppresses BPH multiplication.
► Native PAGE analysis detects five esterase isozymes in BPH with carboxylesterase property.