Field trials were conducted in Thailand to determine the effect of Thai neem seed oil, monocrotophos (Azodrin), and carbosulfan (Posse) on rice yields (Oryza sativa L., variety RD7). Neem-treated plots did not yield significantly more rice than control plots. Plots treated with monocrotophos or carbosulfan had significantly higher yields than control plots or neem-treated plots. The rice yields were correlated with the levels of three insect species: Nephotettix virescens (Distant) (Homoptera: Cicadellidae), Nilaparvata lugens (Stal) (Homoptera: Delphacidae), and Chilo sp. (Lepidoptera: Pyralidae). Only N. virescens exceeded its economic threshold. More than 95% of the variation in yield data could be explained by the N. virescens levels 36 days after transplanting, N. virescens populations were reduced by applications of monocrotophos and carbosulfan. N. virescens was not effectively controlled by neem seed oil. N. virescens control with monocrotophos or carbosulfan at economic threshold appears to significantly increase rice yields.