Patrick Garcia, International Rice Research Institute, Los Baños, Philippines
Zhongxian Lu, Zhejiang Academy of Agricultural Sciences, Hangzhou, China
Insecticide resistance development continues to threaten the sustainability of rice production in Asia. Multiple fold resistance has developd in many countries, especially in China and Vietnam, where insecticide use is particulalry high. In a workshop organized jointly by Zhejiang Academy of Agricultural Sciences (ZAAS) and the Rice Planthopper Project, several advanced methods for insecticide resistance research and monitoring were discussed and planned. These include the use of probit analysis in detecting resistance reversion in time, analyzing the efficacies of insecticide “cocktails” or mixtures and resistance mapping using the single dose technique and the use of RT-PCR. Twenty participants from China, Thailand, Philippines, Malaysia and Vietnam gathered in ZAAS, Hangzhou China from September 5 to 9, 2011 to plan data gathering activities in respective countries. Professor Liu Zemen of Nanjing Agricultural University introduced his work in China to determine the mechanism of imidacloprid resistance in the brown planthopper (BPH). Although resistance to imidacloprid in China is extremely high, most of this is attributed to the detoxification caused by enhancement of P450 mono oxygenases and not irreversible target site mutation. Dr Matsumura of Kyushu and Okinawa Experimental Station in Kumamoto Japan, however suggested that in the Mekong Delta, BPH resistance to imidacloprid might be due to target site mutation. Dr Alvin Hee of Universiti Putra Malaysia discussed the basics of insect physiology to provide better understanding of how insecticide resistance can occur and Dr Tan Keng Hong talked about mechanisms of resistance, factos that accelerate its develoment and management strategies.
Dr K.L. Heong led the discussion on the finer points in using probit analysis and participants practiced analyzing their data under instructions of Patrick Garcia. To monitor and map the geographic distribution of resistance, two methods were planned: the use of single critical dose and the use of PCR. Other studies to be conducted include the analysis of resistance reversion and the analysis of active ingredient mixtures.
Rapid insecticide resistance is occurring in numerous countries and it is causing loss in insecticide effectiveness as well as increase in farmers’ input costs because they would need to apply more. Such rapid development of insecticide resistance is due to misuse as many sprays are applied unnecessarily. In addition insecticides often are used as prophylactics and incorporated as seed dressing for long residual actions thus posing high selection pressures on the planthoppers. Monitoring and better understanding of mechanisms and distributions will help manage resistance development.