Appraisal of the Impact of Three Insecticides on the Principal Rice Pests and Their Predators in China

Abstract

Chemical control is an effective measure for decreasing the numbers of rice planthoppers (Nilaparvata lugens [Stål] and Sogatella furcifera [Horváth]; Hemiptera: Delphacidae) and rice leaffolders (Cnaphalocrocis medinalis Guenée; Lepidoptera: Crambidae), which have caused substantial yield losses of rice in China in recent years. Virtako is a new mixture of insecticides that has low mammalian toxicity and high toxicity to insect pests. We conducted a study of the effectiveness of Virtako (a mixture of chlorantraniliprole and thiamethoxam), versus chlorantraniliprole alone and thiamethoxam alone, for control of rice planthoppers and rice leaffolders, as well as the impact of these insecticides on predator diversity. One and 28 d after application, Virtako treatment (36-60 g a.i./ha) reduced the numbers of planthoppers to 46 to 60% and 59 to 66%, respectively, of the control levels. Virtako also suppressed damage by rice leaffolders, resulting in leaf protection rates of 11 to 46% and 37 to 76% at 7 and 28 d after application, respectively. Both 1 and 2 applications of Virtako per crop cycle caused significant short-term reductions in insect predator populations. However, 21 d after the application of Virtako (36 g a.i./ha), the diversity indices and the total number of predators were similar to those in untreated plots. A single application of Virtako provides good control of insect pests in paddy fields, and predator populations recovered quickly after the Virtako application. Our studies indicated that Virtako might be an effective alternative for the control of planthoppers and rice leaffolders in paddy fields.