By Liu Zewen
Professor, insect neuro-pharmacology
Nanjing Agricultural University
1315-1415 H, Tuesday, 7 August 2012
Room A, D.L. Umali Building, IRRI
The brown planthopper (BPH), Nilaparvata lugens Stål, is a major rice pest in many parts of Asia. Insecticides have been extensively used for control of this pest, and resistance to a number of them has been reported in different countries and areas.
In order to understand the possible mechanisms for insecticide resistances in BPH, resistance selections were carried out in laboratory against to two main insecticides, imidacloprid and fipronil. Under high selection pressure (more than LD75 doses in each generation), the resistance development was found with a phased increase and there were two rapid increase periods, as double “S” shape.
In the first increase period, biochemical factors, such as the high expression of detoxification enzyme genes, were the main mechanisms. However, in the second increase period, the target insensitivity (target site mutation) was the main mechanism.
Insecticide resistance management (IPM) strategies were often used to control insecticide resistances, but these strategies would be only efficient when resistance levels were at the first increase periods with biochemical mechanisms.
In recent years, imidacloprid and fipronil resistances in BPH were monitored in China. Although the resistance ratios were high different from several reports, the biochemical mechanisms were still the main factors contributing to resistances against imidacloprid and fipronil, which indicated that the IPM strategies will still work.
Based on the target site mutations, PCR detection methods were developed to check the possible mutation frequencies in field populations, especially in the field populations with resistances at high or super high levels.