| Rice leaffolder Cnaphalocrocis medinalis Guenee is one of the most important rice insect pests in China. Due to the difficulty in its mass rearing with artificial diets in laboratory, many research activities were constrained. Mass rearing with artificial diet could break the restriction of host plants and season to obtain uniform experimental insects. Some entomologists had conducted many trials on the artifical diets of C. medinalis, unfortunately, the problem had not been completely solved. Feeding preference, consumption and utilization of food, growth and development, changes in digestive enzymes of C, medinalis larvae fed on artificial diets with different contents of nitrogen and sugar were conducted in this study for optimizing the artificial diet formula of C. medinalis. The main results are shown as follows:1) Newly-hatched larvae preferred artificial diet with high sugar, and the number of larvae chose the diet with27.22%sugar was higher than that with16.75%sugar. Nitrogen contents in diet also significantly affected the selectivity of newly-hatched larvae. Sugar content could affect the selectivity of3rd instar larvae and nitrogen content was also affect the numbers of3rd instar larvae on the different diets. The5th instar larvae liked to choose the diet with high sugar (27.22%). There were no obvious differences of5th instar larvae in selecting different nitrogen artificial diets.2) The3rd instar C. medinalis larvae were introduced on the diets with different nitrogen or sugar contents in order to observe the growth and development of C. mednalis larvae. Percentage of C. mednalis larvae developed to5th instar, pupation rate, adult emergence rate and pupal weight are relatively higher and the larval duration is shortter on TNI rice leaves than that on artificial diets with different nitrogen and sugar contents. With the increase of nitrogen content in the diets, the percentage of C. mednalis larvae developed to5th instar decreased and larval duration shortened, while theses indexes were no significant difference on diets with different sugar contents. Pupation rate, emergence rate and pupal weight decrease with increased nitrogen content in diets, while pupation rate, emergence rate increased with increased sugar content in diets and there were no significant difference on pupal weight with increased sugar content in diets.3) Nutritional indexes of3rd instar larvae were not significantly affected by different nitrogen and sugar contents in diets, while the nutritional indexes of5th instar larvae were changed with nitrogen and sugar contents. When nitrogen content were1.53or1.16%, RGR was up to the summit and sugar content was up to16.75%, the RGR was the highest. NUR of3rd instar larvae did not change significantly with the increase of nitrogen contents, NCR of5th instar larvae was highest on the diet with nitrogen content was1.46%, and NUR was lowest when nitrogen content was1.33or1.46%.4) This study focused on the activity of digestive enzymes including trypsin, amylase and lipase, in C. medinalis larvae fed with different artificial diets. Results showed that the trypsin activity of the4th instar larvae varied with nitrogen contents in artificial diets as "V" type, while this trend was not significantly shown in5th instar larvae; amylase of C. medinalis was not changed siganificantly with the nitrogen contents in diets; the5th instar larvae were with stable lipase activity, while the4th instar larvae possessed the highest lipase activity when fed on the diet with1.33%nitrogen content. Fed on diets containing different sugar contents, the trypsin activity was stable with the sugar contents; the amylase activity of the4th instar larvae varied with the sugar content as "V" type, while this trend was not significantly shown in5th instar larvae; the lipase activity of5th instar larvae maintained stable, while lipase activity of4th instar larvae increased with the sugar contents in diets. |
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