Insect deterrent activity of ethanolic leaf extracts of landrace maize and determination of active compounds against Spodoptera littoralis Boisduval (Lepidoptera: Noctuidae)

Abstract

The present work was carried out to gain insight into the chemical defense of maize against phytophagous insects. Leaves of sixteen landrace populations were extracted with ethanol. Deterrent activity of extracts was evaluated on Spodoptera littoralis and Rhopalosiphum padi under laboratory conditions. Most of the ethanolic extracts negatively affected settling of R. padi, but only the extract Xn-69 affected feeding of S. littoralis. Active extracts were combined based on their TLC pattern. Bioassay-guided fractionation using biomass gain (ΔB) and food consumption (ΔI) of S. littoralis showed that the active fraction contained three phytosterols: sitosterol, stigmasterol and campesterol as the major constituents. These compounds might be responsible for the negative effects of extracts on biomass gain through the inhibition of food consumption of S. littoralis larvae. These phytosterols might provide in maize nonpreference resistance mechanism against insect pests.