Consumption and utilization of castor bean leaves treated with neem seed kernel extracts by the cotton leaf worm larvae, Spodoptera littoralis (Boisd.).

Larva of cotton leaf worm, Spodoptera littoralis ate and digested an average of 13.79 and 10.82g, respectively of untreated castor bean leaves during its whole sixth instar. These amounts significantly reduced when larvae were fed on leaves treated with different concentrations of neem seed kernel methanolic extract. The reduction was concentration dependent, i.e., an increase in neem extract concentration caused an obvious decrease in the amount of ingested or digested leaves. The consumption and digestion indices are always negative indicating that treated castor bean leaves are not preferred by S. littoralis larvae for feeding. These indices decreased as the concentrations of neem extract increased. Approximate digestibility in S. littoralis sixth instar larvae averaged 78.50%. This percentage insignificantly fluctuated between 77.71 and 81.08% when larvae were fed on castor bean leaves treated with different concentrations of neem extract. Efficiencies of conversion of ingested and digested food to body substances (ECI and ECD) are an overall indicators for ability of S. littoralis larvae to utilize ingested and digested food for growth and food storage in the insect. Such values depend upon the food digestibility, its nutritional values and the ingestion rates. ECI and ECD in larvae fed on untreated leaves reached 22.25 and 28.25%, respectively. These values decreased after feeding the larvae on treated leaves. The decrease was gradually occurred as the concentration of neem extract increased to reach the minimum value at the highest concentration (0.025%). INTRODUCTION Neem derivatives have a variety of effects against a wide variety of insect pests including antifeedant and feeding deterrenc, growth regulation inhibitor, toxicity and sterility effects (Raguraman and Singh, 1999). Such derivatives are primarily considered as toxicants to larvae or nymphs of phytophagous insects at required concentrations and hence show considerable selectivity toward natural enemies of insect pests such as parasitoids and predators (Awad et al 1998). Therefore, these derivatives have potential for use in integrated pest management. The feeding deterrent activity of Neem Azal-S and Margosan-O ( a pesticidal products of neem seeds) was found to be significant against the adults of Liriomyza trifolii (Burg.), particularly at high concentrations (Dimatry et al 1995). Deka et al (1999) suggested that methanol extract from Melia azadirach showed antifeedant activity to tea mosquito bug Helopeltis theivora. Margosan-O, besides being toxic, also has feeding, and growthinhibitory effects on certain insects (Scott and Kaushik, 1998). Recently, Gomaa, (2009) studied the effects of different concentrations of neem seed kernel aqueous extracts using different types of organic solvents on oviposition deterrency of mated Spodoptera littoralis (Boisd.) female moths in free choice test and the ovicidal action of such extracts on the deposited eggs. He found that the methanol extract is considered as the most active solution as oviposition deterrent and ovicidal compound. The same findings were given by Ayyangar and Rao, (1990) on Spodoptera litura (Fabr.) and Dilawari et al (1994) on diamondback moth, Plutella xylostella.