STUDIES ON SEMISYNTHETIC DIETS OF THE TOBACCO CUTWORM, SPODOPTERA LlTURA (F. )
Lu Wenhua Tang Zhongqi Zhong Weiqiu (Department of Plant Protection)
This Paper deals with semisynthetic diets for mass rearing of Spodopteta litura(F.). Orthogonal layout is used to screen a cheaper, simpler and better diet composition. Six factors, including proportion of the cassava leaf powder and soy bean powder (A), percentage of dry yeast (B) , percentage of asorbfc acid (C) , percentage of sucrose(D), amount of water (E) and agar (F) , each at five different level, were tested by assessing average rate of larval growth, percentage of larval survival and average weight of female pupa.Results showed that dry yeast in the diets played an important role in larval growth, survival and pupal weight of Spodoptera litura (F. ) with its optimal concentrations between 20%-25%. Asorbic acid was essential for adult's fecundity since the average weight of female pupa is obviously good with 1% concentration. The percentage of larval survival was also affected by the amount of water, the optimal level being about four times of the dry dietary components in the diets.It was no necessary to supplement sucrose to the diets. Larval growth and survival were not adversely affected when agar amount fell from 2 % to 1.5%. The suitable diet composition is as following, cassava leaf powder, 790g; soy bean powder,395 g; dry yeast,300 g, asorbic acid, 15 g, water, 6000 ml and 90 g agar. It could be prepared for rearing 1200-1500 larvae.Further experiment showed that there was a linear correlation between the female pupal weight and the number of eggs laid by Spodoptera litura (F. ) , r = 0.99225.