Pentacyclic Triterpenoids and a Linear Alkane from the Milky Mangrove Tree (Excoecaria agallocha L.) are toxic to the larva of Helicoverpa armigera Hubner. (Lepidoptera: Noctuidae)

Throughout the world, as a part of the Integrated Pest Management (IPM), botanicals are evaluated for its efficacy against the polyphagous Pink Bollworm Helicoverpa armigera Hubner. In our present study, hexane extract of the dry leaves of the milky mangrove tree Excoecaria agallocha L. exhibited dose-dependent growth inhibition of late 2nd & early 3rd instars larvae of H. armigera under in vitro conditions. 0.1% of crude hexane extract of E. agallocha leaf caused 50% mortality of early 3rd instars larvae of H. armigera (LC50-0.0001g/kg body weight), compared to synthetic pesticide Ekalux® (90%) & the solvent control (12%). 2% extract dosage reduced the healthy adult moth emergence to 2% compared to Neem® control (14%). Out of the 7 column fractions (SiO2 60-120 mesh, Eluent: Petroleum Ether: Ethyl Acetate) tested, fractions 1, 4 & 5 suggested growth inhibition (75, 90 & 94%). The bioactive fractions were characterized using FT-IR, NMR, Mass Spectrum & X-ray Crystallography as known linear alkane n-Hentriacontane (fraction-1), pentacyclic triterpenoids Taraxerone (fraction-4) & Taraxerol (fraction-5). Purified n-hentriacontane, exhibited 80% mortality with a reduced larval weight (280 mg) compared to crystalline taraxerone (75%, 151.7 mg), while taraxerol exhibited 80% larval mortality (Mean larvae weight: 64 mg), compared to the controls (416.5 mg on average). Transverse Sections (T.S.) of the midgut of H. armigera larvae treated with the bioactive fractions suggested drastic shrinkage & lysis of the gut wall, leakage of exocrine secretions & the micronuclei. Further studies would suggest the possibility of formulating a potential phytochemical pesticide from E. agallocha against lepidopteron pests.