Tunisian Journal of Plant Protection (Jun 2016)
Effect of olive leaf extracts on the feeding, growth and metabolism of Spodoptera littoralis. Ben Hamouda, A., Boussadia, O., Bedis, K., Chaieb, I., Laarif, A., and Braham, M. (Tunisia)
Abstract
In the present study, methanol and acetone crude extracts of olive leaf were investigated for their antifeedant activity, growth and metabolism inhibitory against the cotton leaf worm, Spodoptera littoralis under laboratory conditions. Two feeding tests: leaf discs and artificial diet at three concentrations (0.1, 1 and 10%) of each extract, were implemented in the experiment. Results revealed that the leaf discs bioassay was more effective than the artificial diet bioassay for the antifeedant activity and the weight loss of S. littoralis larvae. Acetone and methanol extracts caused strong antifeedant activity at 10% with 68.33 and 61.44%, respectively. Tests performed on growth generated a very pronounced inhibition of growth gain using leaf disc test for the two extracts and at all tested concentrations. Data indicated that the lowest relative consumption rate (RCR) and the relative growth rate (RGR) were recorded using acetone extract at 10% for leaf discs bioassay (5.88 ± 0.75 and 0.07 ± 0.05 mg/mg/day, respectively). The efficiency of the conversion of ingested food (ECI) and the efficiency of conversion of digested food (ECD) were significantly lowered using methanol extract at 10% in artificial diet bioassay (2.5 ± 0.58 and 2.55 ± 0.6%, respectively). The highest approximate digestibility (AD) of S. littoralis larvae was found in both extracts for the artificial diet bioassay. Moreover, larvae exposed to 10% methanol extract in artificial diet test exhibited a delayed growth rate by 17.7 days, relative to control at the same concentration, compared to 5.7 days noted using acetone extract in leaf disc test. The antifeedant activity, growth and metabolism parameters are appropriate tools in feeding tests and extracts’ activity evaluation. They could provide profound understanding of the choice of the best plant extracts that could be proposed as bioinsecticides in a more environmentfriendly approach.
