Patrick Garcia, International Rice Research Institute, Los Baños, Philippines
Insecticide applications continue to be the main means of pest management in rice production. In China farmers apply huge amount of insecticides in routine schedules often up to 10 times a season. In recent years, planthoppers, both the brown and the whitebacked planthoppers, have become serious problems. In the tropics, scientists recognize these as secondary pests and when they become problematic, it is because of the breakdown in ecosystem services due to insecticide misuse. Insecticide overuse is also causing rapid development of resistance and in China, the brown planthopper is reported to have acquired hundred folds in insecticide resistance to some active ingredients. In his recent visit to IRRI, Professor Zewen Liu delivered a seminar on insecticide resistance research in China of two chemicals, imidacloprid and fipronil, and the biochemical mechanisms involved.
Resistance to the two active ingredients developed rapidly in China resulting in the removal from the market. Imidacloprid was in the market from 1997 to 2005 and fipronil from 2007 to 2009, which is being replaced by the more environmentally friendlier butene-fipronil. The rapid loss in use of imidacloprid is due in part to misuse as some describe this fall from grace as “from hero to zero” and its high toxicity to pollinators recently confirmed by two SCIENCE papers.
The resistance development was found to have 2 stages known as the double “S” curve. 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. Methods to manage resistance would only be efficient when resistance levels were at the first increase stage associated with biochemical mechanisms.
In China, imidacloprid and fipronil resistances in BPH are probably still due primarily to stage 1 biochemical mechanisms. Thus, strategies to withdraw these chemicals before resistance reaches the second stage can still be used for management. Although low frequencies of stage 2 target resistance might have occurred in some places. IRRI and its collaborators led by Dr. K.L. Heong are now exploring RT-PCR detection methods to be used to check for these possible mutation frequencies in different field populations of Thailand, Vietnam, Philippines, and China.