The Research On The Artificial Diet Of Rice Leaffolder, Cnaphalocrocis Medinalis (Guenee)(Lepidoptera:Pyralidae)

The rice leaffolder (RLF), Cnaphalocrocis medinalis (Guenee), is one of the most important insect pests on rice. However, the mass rearing of RLF with an artificial diet is an extremely hard task. Although many attempts had been made to improve the artificial dietsin the past years, there still existed many problems. The key problem was the high mortality of the neonate larvae on an artificial diet. Meanwhile both mold prevention and toxicity of the antimicrobials were important factors in insect rearing program,whichmight prevent the normal development of larvae. Therefore, our experiments were designed to screen the available new antifungal agents and to determine whether they could successfully control the mold. Besides, we wanted to find out if it was suitable for RLF rearing. This research was also undertaken to study the effects of water content and the dietary additives including antibiotics, sucrose, cholesterol, vitamin mixture, rice leave powder, plant oils and others, in the artificial diet on the growth and development of C. medinalislarvae.The rice leaffolder, C. medinalis is difficult to rear with artificial diets in laboratory, which might be caused by the antifungal agents used in the diets, the successful rearing of C. medinalis need "safer" antifungal agents.In this study, nineteen antifungal agents including 7 food preservatives,6 agricultural fungicides and 6 antifungal drugs are assayed for the inhibitory activities against the growth of Aspergillus flavus and Aspergillus niger on RLF artificial diets. The results showed that dehydroacetate、natamycin、fludioxonil、 chlorothalonil、prochloraz、tebuconazole、azoxystrobin and voriconazole wereeffective. Natamycin is the best one tested in this assay, which completely prevent the mold growth for 20 days at the concentration of 300 ppm. The inhibitory effect of natamycin issuperior to sorbic acid and methylparaben.Dehydroacetate also has good antifungal effect comparable to sorbic acid, moreover superior tomethylparaben.But most of the chemicals were unsuitable as mold inhibitors in the diets of the rice leaffolder. The mixed use of natamycin and sorbic acid, sorbic acid and methylparaben resulted in a higher larva survival and pupation rate. The ternary combination of natamycin, sorbic acid and methylparaben was the best combination for the rearing of rice leaffolder.The effects of dietary additives in artificial diets on the larval growth of C. medinalis were evaluated.Antibiotics, ascorbic acid and vitamin mixture in the medium were indispensable for the survival and growth of C. medinalis larvae. Additions of cholesterol, and sucrose to the artificial diets improved the development of C. medinalis larvae. Incorporation of rice or corn leave powder and plant oils increased the larval mortalities, and reduced the pupation of C. medinalis larvae.The addition of Wesson’s salt didn’t improve the larval survival and growth on artificial diets.Put all of our results and previous investigations together, a recipe to rear C. medinalis could be proposed as follows:Agar 1.2%, wheat germ 4.8%, soybean powder 4.8%, casein 1.6%, yeast 3.2%, sucrose 2.4%, cholesterol 0.08%, methylparaben 0.08%, sorbic acid 0.08%, ascorbic acid 0.16%, natamycin 0.024%, vitamin mixture 0.16%, chloramphenicol 0.0125%, adding water to 80.0%. The continuous rearing of RLF with this artificial diet is still under evaluation in our laboratory.