Effects of triazophos on biochemical substances of transgenic Bt rice and its nontarget pest Nilaparvata lugens Stål under elevated CO2

The brown planthopper (BPH), Nilaparvata lugens Stål, is a serious rice pest throughout Asia. Recent outbreaks of N. lugens populations were mainly associated with the overuse of pesticides and resistance to insecticides. Warmer global temperatures that are associated with anthropogenic climate change are likely to have marked ecological effects on terrestrial ecosystems. However, the effects of elevated CO2 concentrations on the biochemical, physiological and nutrient quality of transgenic Bt rice that has been treated with pesticides and on the control efficacy of the pesticides are not understood. The present study investigated changes in soluble sugar content, free amino acid levels, oxalic acid levels, flavonoids levels, and triazophos residues in transgenic Bt rice (TT51) and the control efficacy of triazophos for N. lugens following triazophos foliar spray under conditions of elevated CO2 (eCO2). Our findings showed that the soluble sugar content of TT51 treated with triazophos under eCO2 was significantly higher than that under ambient CO2 (aCO2) and also higher than that of the non-transgenic parent (MH63) under aCO2. However, the results for free amino acid levels were the opposite of those for soluble sugar levels. The oxalic acid and flavonoid contents of rice plants significantly decreased with increases in triazophos concentration, CO2 concentration, and days after treatment (DAT). The oxalic acid and flavonoid contents of TT51 treated with triazophos under eCO2 were significantly lower than those under aCO2 and also lower than those of MH63 under aCO2. The residue concentration of triazophos varied with CO2 concentration, rice variety, and DAT. The residues in TT51 treated with 80ppm of trizaopos under eCO2 were significantly lower than those under aCO2 and those in MH63 under aCO2. The survival rate of nymphs N. lugens in TT51 under eCO2 was significantly higher than that under aCO2 and that in MH63 under aCO2 at 1 DAT or 15 DAT after the release of 2nd instars nymphs. These findings indicated that (1) for TT51, triazophos reduced the resistance of rice plants to N. lugens with an elevated CO2 concentration, as N. lugens consumed more phloem sap on TT51 plants; (2) triazophos dissipation in TT51 under eCO2 was significantly faster than that under aCO2 and that in MH63 under aCO2; (3) the control efficacy of triazophos for N. lugens significantly decreased under eCO2. The present findings provide important information for integrated pest management among transgenic varieties.