Effect of Moringa oleifera lectins on survival and enzyme activities of Aedes aegypti larvae susceptible and resistant to organophosphate

The indiscriminate use of synthetic insecticides to control Aedes aegypti has led to emergence of resistant populations. Moringa oleifera seeds contain the lectins WSMoL and cMoL. WSMoL has larvicidal activity on fourth-stage of A. aegypti organophosphate-susceptible larvae (Rockefeller L-4). This study reports on the effects of cMoL on the survival of Rockefeller L-4 as well as of WSMoL and cMoL on L-4 from an organophosphate-resistant population (Rec-R). The effects of lectins on digestive (amylase, trypsin, and protease) and detoxifying (superoxide dismutase (SOD), alpha- and beta-esterases) enzymes from larvae were also determined. cMoL (0.1-0.8 mg/ml) did not kill Rockefeller L-4 as well as WSMoL and cMoL (0.1-0.8 mg/ml) were not larvicidal for Rec-R L-4. WSMoL stimulated protease, trypsin-like, and alpha-amylase from Rockefeller L-4 while cMoL inhibited these enzymes. WSMoL had no effect on trypsin-like activity from Rec-R L-4 but inhibited protease and alpha-amylase. Among digestive enzymes of Rec-R L-4, cMoL inhibited only trypsin-like activity. cMoL inhibited SOD activities from Rockefeller and Rec-R L-4 in a higher level than WSMoL while beta-esterase from Rockefeller L-4 was more inhibited by WSMoL. The lectins promoted low stimulation or inhibition of alpha-esterase activities from both populations. In conclusion, Rockefeller and Rec-R larvae were distinctly affected by M. oleifera lectins, and larvicidal mechanism of WSMoL on Rockefeller L-4 may involve deregulation of digestive enzymes. cMoL interfered mainly on SOD activity and thus it can be investigated as a synergistic agent for controlling populations whose resistance is linked to an increased detoxifying process mediated by this enzyme.