Tolerance potential of Chilo suppressalis larvae to fipronil exposure via the modulation of detoxification and GABA responses

- The stem borer possesses tolerance potential to fipronil through changed physiology.
- Fipronil at low concentrations provides the selective pressure for larvae tolerance.
- The activity of detoxification-related enzymes shows increased response to fipronil.
- GAD activity and GABA level in the borers are improved by fipronil exposure.

The Asiatic rice borer, Chilo suppressalis Walker, is one of the most destructive rice pests in the world; its physiological adaptability to the sustained application of fipronil was investigated. After topical application, fipronil showed strong lethal effect with LD20 and LD80 values on the fourth instar larvae as 0.00159 and 0.00906 μg per larvae at 48 h- post treatment, and also revealed slight inhibition on the eclosion of pupae and the hatching of eggs. LD20 dosage of fipronil significantly enhanced the activities of carboxylesterase (CarE), glutathione-S-transferase (GST) and cytochrome P450-linked p-nitro O-demethylase (PNOD) in the borers. LD80 dosage of fipronil showed a mild decrease on the activity of CarE, GST and PNOD, and a slight suppression on the activity of glutamate dehydrogenase (GDH), but strongly induced the transform of glutamate to gamma-aminobutyric acid (GABA) and the activity of glutamate decarboxylase (GAD), thereby improved GABA level in the bores. Results suggested that the borer possessed positive tolerance potential to firponil via the modulation of detoxification and GABA responses and provided the basis for further studies on reducing the tolerance of the borer in the control strategies.

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