Resistance monitoring and assessment of resistance risk to pymetrozine in Laodelphax striatellus (Hemiptera: Delphacidae).

Laodelphax striatellus (Fallén) is a major pest of cultivated rice. Pymetrozine, a pyridine azomethine compound, represents a novel insecticide with a selective activity against sucking pests. The resistance of L. striatellus to thiamethoxam, nitenpyram, chlorpyrifos, and pymetrozine in five field populations, collected from Jiangsu, Anhui, and Zhejiang in China, was monitored from 2009 to 2011 in laboratory. All the populations kept susceptible to minor resistance to thiamethoxam and nitenpyram in the 3 yr (0.6- to 2.2-fold and 0.8- to 3.8-fold, respectively), while the insects developed low to high level resistance to chlorpyrifos (9.7- to 76.1-fold). Three populations were all susceptible to pymetrozine (1.1- to 2.1-fold) in 2009, but the Wuxi and Yancheng populations developed low level resistance to pymetrozine (5.5-fold and 5.3-fold, respectively) in 2011. Meanwhile, the resistance level of the selected strain reared in laboratory increased by 1.0-fold after 12-generation selection with pymetrozine. The realized heritability (h2) of resistance at different selection stages was estimated as 0.0470 (F1 to F13) and 0.2070 (F5 to F13) by using threshold trait analysis. It suggested that L. striatellus had the definite risk of resistance to pymetrozine.