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Plants accumulate phenolic compounds such as tannic acid to resist insect herbivores. The survival of insects exposed to toxic secondary metabolites depends on the detoxification metabolism mediated by limited groups of glutathione S-transferases (GSTs). <i>Micromelalopha troglodyta</i> (Graeser) (Lepidoptera: Notodontidae) is an important foliar pest of poplar trees. GSTs play an important role in xenobiotic detoxification in <i>M. troglodyta</i>. Five GST genes were identified in <i>M. troglodyta</i> and were classified into five different cytosolic GST classes, delta, omega, sigma, theta, and zeta. Real-time fluorescent quantitative polymerase chain reaction (qPCR) was used to determine the mRNA expression of the five cloned GSTs in the midguts and fat bodies of <i>M. troglodyta</i>. The mRNA expression of the five GSTs was significantly induced when <i>M. troglodyta</i> was exposed to tannic acid. To further understand the tannic acid regulatory cascade, the 5′-flanking promoter sequences of the five <i>MtGST</i>s were isolated by genome walking methods, and the promoters were very active and induced by tannic acid. In summary, the induction of GST mRNA expression was due to the response of five <i>MtGST</i> promoters to tannic acid. Therefore, <i>MtGST</i> promoters play an important role in the regulation of GST transcription.