Insights in to the successful semi-synthetic diets for invitro mass rearing of spotted pod borer, Maruca vitrata (Crambidae: Lepidoptera)

Spotted pod borer Maruca vitrata Fabricius (Lepidoptera: Crambidae) is a serious pantropical pest of legume crops. Though several diets were tried in different parts of the world, none of them contained black gram flower and seed powder as a component from natural host. Four semisynthetic diets (D-J: Soybean and Cowpea based diet; D-JR: Cowpea based diet; D-New: Soybean based diet; D-B: Black gram based semi synthetic diet) and natural black gram flowers and pods were tested to evaluate the nine biological parameters: durations of larva, pupae and adult, larval and pupal weight, sex ratio, fecundity, adult emergence, larval and pupal growth index, food consumed, fecal weight and total developmental period. The seven nutritional indices were determined: relative growth rate, consumption rate, metabolic rate, approximate digestibility, efficiency of conversion of ingested food, efficiency of conversion of digested food and metabolic cost. Larval development showed a significant difference among the diets. The results indicated that third instar larvae fed on a D-B diet recorded the shortest developmental time (29.37 days) and the highest food consumption (64.21 mg) and fecal production (20.83 mg), resulting in the maximum larval and pupal weights (48.46 and 47.11 mg, respectively). The black gram-based semisynthetic diet was highly suitable for the continuous rearing of M. vitrata compared to other semisynthetic diets to produce uniformly sized insects of predictable performance without a loss of vigor or a decline in reproductive potential. D-B diet can be used as an efficient alternative to natural diet for rearing in laboratory conditions.