Susceptibility baseline and chlorantraniliprole resistance monitoring in Chilo suppressalis (Lepidoptera: Pyralidae).

Chlorantraniliprole, a new anthranilic diamide insecticide, has been commercialized in China since 2008 for controlling of several lepidopterans, including rice stem borer, Chilo suppressalis Walker. Chemical control of this pest has become difficult because of its resistance development to many conventional insecticides. To facilitate chlorantraniliprole-resistance monitoring, seedling dip bioassays were conducted in 2011 and 2012 to assess the susceptibility of 30 populations of C. suppressalis from seven provinces in China. The assays established a larval susceptibility baseline with LC50 at 1.393 mg a.i/liter. The toxicity (LC50) of chlorantraniliprole against second-instar larvae of field populations ranged from 0.568 (SL12) to 13.547 (RA12) mg a.i/liter. Substantial variations of the susceptibility to chlorantraniliprole were detected among different geographic populations, but no significant difference was observed between years for most populations except for populations from Dong'an, Cangnan, and Lujiang. Resistance ratios to the chemical ranged from 1.0 to 9.7, indicating that most colonies remained susceptible or showed certain decrease in susceptibility. Approximately, 13.3% of the populations exhibited low levels of resistance to chlorantraniliprole. These data are useful in future monitoring program for detecting any changes in susceptibility as a result of use of the insecticide.