Insect Growth Inhibitory Activity of Clerodane Diterpenoids Isolated from Clerodendron infortunatum L. on the Cotton Bollworm, Helicoverpa armigera (Hubner)

Abstract

Three clerodane diterpenoids were isolated from the medicinal plant, Clerodendron infortunatum and their growth inhibitory activity was evaluated against Helicoverpa armigera through topical as well as diet incorporation method and the results compared with azadirachtin technical (20 %). Different parameters were used to assess the growth inhibitory effects, such as larval mortality, pupal mortality, larval–pupal intermediates, abnormal pupae, pupal–adult intermediates, larval and pupal weight reduction and larval and pupal durations. The growth inhibition activity in the present study was compared based on growth inhibition index (GI50). It was observed that through topical application clerodin (1), 15-methoxy-14,15-dihydroclerodin (2) and 15-hydroxy-14,15-dihydroclerodin (3) showed 13, 21 and 11 ppm GI50 values, respectively, compared to azadirachtin with GI50 value of 15 ppm. Through diet incorporation method, azadirachtin showed complete growth inhibition even at the lowest concentration (10 ppm) and more than 50 % growth inhibition was recorded at the lowest concentration of the pure compounds. Results showed that C. infortunatum can be considered as an important plant to develop botanical biopesticides. Effect of isolated compounds on various parameters of insect growth inhibition is discussed.