Influence of food plants on growth and development and susceptibility to insecticides of Spodoptera littoralis (Boisduval)
A series of experiments was conducted to evaluate the responses of S. littoralis (Boisd) to seven plants species. Probable factors responsible for the preference for some of the food plants were determined. In multiple-choice preference tests, both 1st and 4th instar larvae preferred dicotyledonous to monocotyledonous plants. First instar larvae rejected millet. In two-choice tests using maize, millet and sorghum, the larvae always preferred maize. Studies on growth and development of the larvae on the food plants were carried out. The larvae failed to develop to the pupal stage on millet. Growth was adversely influenced on maize and sorghum. Only 7% of the neonate larvae on sorghum and 32% of the larvae on maize developed to the adult stage. Food digestion and utilisation studies indicated low food intake, digestion and utilisation of food by larvae on maize, millet and sorghum. Analysis of the plants showed that differences in the larval performances on the plants could be due to both nutritional and allelochemical factors. There were more deterrent leaf extracts in the plants that reduced larval growth. Nitrogen, amino acids and the water content of the plants were lower in the monocot than the dicot plants. The total P-450 content and larval susceptibility to insecticides were influenced by the plants fed on by the larvae. Scanning of microsomal preparations showed that the variations in the peptide profiles of the microsomes were associated with the P-450 contents of the plants. Piperonyl butoxide, barbital and ß-naphthoflavone affected feeding of the last larval instar.