Influence of Dietary Vegetable Oils on the Tobacco Cutworm, Spodoptera litura (Fabricius) and its Nuclear Polyhedrosis Virus Production

Investigations were-carried out on the impact of certain vegetable oils, viz., castor, coconut, cottonseed, groundnut, mustard, safflower, sesamum, soybean, sunflower and linseed added at the rate of 0.6 per cent in the semi-synthetic diet on the tobacco caterpillar, Spodoptera litura (Fabricius). The results revealed that the vegetable oils (0.6 %) did not have any effect on larval and pupal duration, fecundity and egg period of the insect. However, the yield of NPV was significantly increased by the addition of mustard and coconut oils to the standard diet. When early fifth instar larvae were inoculated with a dose of 1966.18 POB/mm² of diet surface, diet incorporated with 0.6 per cent coconut oil yielded the highest number of 8.7xl0⁹ POB/larva which was significantly higher than that obtained from larvae fed on standard diet. At the higher inoculum level of 3932.96 POB/mm², mustard oil recorded the highest virus yield of 7.4xl0⁹ POB per larva. But incorporation of mustard oil in the diet reduced the fecundity in S. litura moths significantly and hence mustard oil cannot be used in host culture. Also, by incurring an additional cost of Rs. 0.30/- by adding 0.6 per cent of coconut oil, to the diet, an increase in yield upto 12.9x10¹¹ POB/200 larvae (4.3 fold increase) was obtained. The results indicate that the insects can be mass produced in the standard diet, and for virus production mustard and coconut oils can be used as dietary adjuvant at 0.6 per cent to the standard diet.