Abstract: 【Aim】 Chitinase and chitin synthetase are of great importance to the metamorphosis in insects. This study aims to elucidate the effects of momordicin I on the expression of chitinase and chitin synthase genes in Spodoptera litura and its growth and development. 【Methods】 The expression levels of chitinase gene (SlCht) and chitinase synthase gene (SlCHS-A) in different developmental stages (egg, larva, prepupa, pupa and adult) and tissues (integument, midgut, fat body, hemocyte, head and Malpighian tubules) of the 4th-6th instar larvae of S. litura, and in various tissues of the 6th instar larvae at 24, 48 and 72 h after injection with momordicin I solution (4 μg/individual) were detected by RT-qPCR. The effects of injection of momordicin I at different concentrations (31.25, 62.5, 125, 250 and 500 ng/individual) into the 4th instar larvae of S. litura on the larval and pupal duration, larval weight gain, pupal weight, pupal length, pupation rate, emergence rate and survival rate were analyzed, and the phenotypic changes of S. litura larvae were also observed under stereoscopic microscope. 【Results】 SlCht and SlCHS-A showed developmental stagespecific expression in S. litura, both with the highest expression levels in the egg stage but significantly lower expression levels in the larval and prepupal stages, and with the highest expression level in the 6th larval instar during the larval stage. SlCht and SlCHS-A also exhibited tissue-specific expression in the 6th instar larvae of S. litura, both being highly expressed in hemocyte and integument, and lowly expressed in head, midgut and fat body. Injection of momordicin I into the 6th instar larvae of S. litura induced the decreased expression of SlCht and SlCHS-A genes in their various tissues. After injection of momordicin I into the 4th instar larvae of S. litura, the growth and development of S. litura were inhibited, the larval weight gain was delayed, the developmental duration was prolonged, the pupation rate was decreased and even failure to pupate was observed, and high malformation rates of larvae and pupae were found. 【Conclusion】 Momordicin I can inhibit the growth and development of S. litura by inducing the decreased expression of SlCht and SlCHS-A. This study provides a new theoretical basis for further elucidation of the inhibitory mechanism of momordicin on the growth and development of S. litura, and lays a foundation for the application of momordicin I in the prevention and control of this insect pest.

Key words: Spodoptera litura, momordicin I, chitinase, chitin synthase, gene expression, growth and development