Abstract: The common cutworm, Spodoptera litura is an important agricultural pest, which has spread out worldwide. It undergoes larval-pupal metamorphosis in the life cycle. As a major organ for food digestion and nutrient absorption, the midgut is degraded and reconstructed during the metamorphosis to adapt to the dramatic change in food type between larvae and adults. Therefore, the substances and energy metabolism in the midgut change accordingly. In order to study the sugar metabolic dynamics in the midgut during metamorphosis, twelve glycometabolism-related genes were identified from the midgut EST library of S. litura. Three of them were cloned to obtain their full cDNAs. The mRNA expression profiles of all the 12 genes were examined by realtime or semi-quantitative PCR in the midgut during metamorphosis, and their mRNA levels in response to the induction of hormones and starvation were also quantified. The results indicated that the open reading frames of α-L-fucoside fucohydrolase, N-acetylglucosamine-6-phosphate deacetylase and enolase genes are 1 461, 1 200 and 1 299 bp, and the predicted proteins are 56.3, 43.3 and 46.7 kDa, respectively. The mRNA expression profiles revealed five different patterns: (Ⅰ) High expression only in the larval stages, including salivary maltase precursor, glycosyl hydrolase family 31 protein, mitochondrial aldehyde dehydrogenase and β-1, 3-glucanase genes. (Ⅱ) High expression only in the prepupal stage, including β-glucuronidase and β-N-acetylglucosaminidase 3 genes. (Ⅲ) High expression only in the pupal stage, including glucosamine-6-phosphate isomerase gene. (Ⅳ) High expression both in the prepual and pupal stages, including glucosidase, α-amylase, N-acetylglucosamine-6-phosphate deacetylase and α-L-fucoside fucohydrolase genes. (Ⅴ) Stable expression, including enolase gene. This indicates that significant changes happen in glycometabolism in the midgut during metamorphosis. Juvenile hormone (JH) had no obvious effect on the mRNA level of these genes. However, 20-hydroxyecdysone (20E) suppressed the mRNA level of type I gene such as glycosyl hydrolase family 31 protein gene, and up-regulated the type Ⅲ gene (glucosamine-6-phosphate isomerase gene). In addition, the mRNA level of all the genes was significantly suppressed by starvation. The results suggest that the dynamics of mRNA level of sugar metabolic genes may be controlled by both 20E and starvation-related factor. These findings in glycometabolism will contribute to elucidating the mechanism of larval-pupal metamorphosis.

Key words: Spodoptera litura, metamorphosis, glycometabolism, juvenile hormone, starvation, gene expression, midgut