Effect of natural and artificial diets on the susceptibility of larvae of the maize stalk borer, Chilo partellus (Swinhoe). to different insecticides

The maize stalk borer, Chilo partellus (Swinhoe) was reared on natural hosts, viz., maize (Zea mays L.) and sorghum (Sorghum vulgare Pers.) plants, and artificial diets compounded with green gram, Vigna rodiata (L.) Wilczek + dew gram, Vigna aconitifolia (Jacq.) Marichat + sorghum leaf powder, and green gram + dew gram as principal base-ingredients. The freshly hatched larvae obtained from the insects reared on these natural and artificial diets were exposed to 24, 48, 72, 96, 120, and 144-hr old insecticidal films formed on 11 ± 1-day old potted maize plants. Two concentrations (0.05, 0.1 per cent) of each of the six insecticides, viz., carbaryl, endosulfan, quinalphos, fenpropathrin, fenvalerate and flucythrinate were evaluated against freshly hatched larvae of C. partellus. There was 100% mortality on 24-hr-old films of each of the two concentrations of different insecticides regardless of the rearing medium. The effect of food,was clearly pronounced when the larvae were reared on two artificial diets, the per cent mortality being significantly high as compared to those reared either on maize or sorhgum. Larvae reared on maize were more tolerant to insecticides than those maintained on sorghum plants. Endosulfan 0.1 per cent was the most toxic to larvae reared either on artificial diets or natural host plants. The least effective insecticides were carbaryl and quinalphos (0.05%) regardless ofthe source of food on which larvae were reared. The duration of ellectiveness of different insecticidal concentrations against larvae reared on different food media was almost the same, when the data were subjected to three types of analyses, viz., (i)analysis of variance, (ii) probit analysis, and (iii) PT-calculations. Of course, the analysis of variance does not involve any assumptions and provides detailed comprehensive information on every aspest of the problem.