Management of stemborers (Lepidoptera: Crambidae) using foliar-applied chlorantraniliprole in rice

Rice is one of the most important crops in Louisiana and Texas, USA. It is subjected to various insect pests throughout the growing season. Lepidopteran stem-boring pests including the Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), are increasing in economic importance as insect pests in rice production, particularly in southwest Louisiana, USA. Field trials were conducted in Louisiana and Texas to examine the efficacy of foliar-applied insecticides (chlorantraniliprole and the pyrethroids zeta-cypermethrin and lambda-cyhalothrin) and chlorantraniliprole seed treatment for control of rice stemborers during 2018 and 2019. Furthermore, a diet incorporation assay assessed the toxicity of chlorantraniliprole to laboratoryreared E. loftini. Results of field experiments in Louisiana showed foliar applications of chlorantraniliprole, at 22 to 35 d after permanent flood was established, reduced stemborer injury to rice by 57.9 to 96.5% in 2018 and 73.9 to 87.5% in 2019 compared to nontreated or pyrethroid-treated field plots. However, rice yields in 2019 did not vary among insecticide-treated and nontreated plots. In the Texas field experiments, chlorantraniliprole applied as seed treatment reduced stemborer injury, but was not effective in reducing injury when sprayed directly to soil after planting or when applied at permanent flood. The LC50 and LC90 (lethal concentration that produced 50% and 90% mortality, respectively) of chlorantraniliprole on third-instar E. loftini were 0.09 +/- 0.03 and 0.53 +/- 0.17 mu g a.i. mL(-1), respectively, at 6 d after exposure. At 10 d after exposure, LC50 and LC90 were 0.04 +/- 0.02 and 0.16 +/- 0.04 mu g a.i. mL(-1), respectively. In addition to chlorantraniliprole seed treatment, foliar application of chlorantraniliprole in rice could provide a new tool for management of damaging stemborer infestations.