Lu Zhong Xian, Zhejiang Academy of Agricultural Sciences (ZAAS), Hangzhou, PR China, Ling Yan and Long Liping, Guangxi Academy of Agricultural Sciences, Naning, PR China and Patrick Garcia, International Rice Research Institute, Los Baños Philippines
We monitored fipronil resistance in BPH populations in Guangxi province in 2009 and 2010 and found that the LD50 values had more than doubled from 2.52 to 5.56 mu g/g insect. The heterogeneity factors of the two probit lines were 0.6 and 0.3 respectively and their slopes were 1.84 and 1.85, respectively. The doubling of resistance had occurred despite of government’s banning the use of fipronil from July 1, 2009. This might be due to fipronil use remaining high despite of the ban or that the fipronil resistant BPH were migrants from Northern Vietnam. In Northern Vietnam fipronil continues to be recommended for seed dressing applications “to prevent infections by virus diseases”, leaf folder and stem borer control in the early crop stages. This practice is said to have stimulated rapid resistance development (Read: BPH highly resistant to fipronil).The practice has been discouraged in the Mekong but the LD50 of BPH populations was still about 1.3 times that of Guangxi in 2009. We however do not have recent toxicological data from Northern Vietnam although work by Matsumura et al (2009) showed that in 2006 the LD50 was less than 0.5 mu g/g insect.
Fipronil is a broad spectrum insecticide that disrupts the insect central nervous system by blocking the passage of chloride ions through the GABA receptor and glutamate-gated chloride channels (GluCl). It is known to be highly toxic to fish, aquatic invertebrates, hymenopterans, especially bees and parasitoids and birdlife. China banned the use of fipronil because of its harmful effects on shellfishes and bees and its slow degradation in water and soil (Read: China bans Fipronil ). In France, fipronil was banned in 2004 because of concerns about the harmful affect of fipronil on bees (Read: France bans Fipronil).
In 2006 LD50 of BPH to fipronil had been less than 1.0 mu g/g insect in Vietnam (Matsumura and Sanada-Morimura, 2010) but in 2009 the LD50 values in Vietnam had increased to 2.52 mu g/g insect. In Northern Vietnam fipronil is commonly applied as prophylactic applications in the early crop stages for leaf folders, stem borers as well as WBPH which is a primary factor inducing rapid development of resistance. With the expected decline in fipronil use in China following its ban, it is possible that the high resistance recorded in China might be due to immigrations from Northern Vietnam. However toxicological data from Northern Vietnam is required to confirm this.
Meanwhile in Thailand and the Philippines LD50 values for fipronil on BPH have remained at less than 1 mu g/g insect.