Changes in juvenile hormone titres and differential expression of related genes at different stages of Coccinella septempunctata L. female adults supplied with an artificial diet and aphid diet

Juvenile hormone (JH) regulates multiple physiological functions in insects including growth, metamorphosis, and reproduction. Juvenile hormone epoxide hydrolase (JHEH) and juvenile hormone esterase (JHE) are degradative enzymes that metabolise JH, and JH receptor (methoprene-tolerant, Met) functions in the regulation of female reproduction and vitellogenesis. In this study, JH titres in Coccinella septempunctata adult females were determined using ultra high-performance liquid chromatography and tandem mass spectrometry; the JH titres ranged from 0.03 to 0.16 ng g^-1 in 5- to 30-day-old female adults. JHEH, JHE, and Met expression were studied in different reproductive stages of C. septempunctata females by quantitative real-time PCR. JHEH transcription levels were highest in 25-day-old female adults and were 1.93-fold higher than expression levels in 5-day-old adults. JHEH and JHE expression levels were inhibited by the addition of JH to the artificial diet. Met expression in C. septempunctata supplied with 3 μl JH in artificial diet was similar to Met transcription in females supplied with an aphid diet, and the results showed that supplementation with 3 μl JH in 582.2 g of artificial diet was the most suitable for reproductive regulation of C. septempunctata. The results of this study provide important insights for the improvement of C. septempunctata artificial diets.