Phytochemical characterisation and toxicity effect of Tithonia diversifolia (Hemls.) A. Gray leaf extract on fall army worm Spodoptera frugiperda (JE Smith) larvae.

Abstract

Objectives: To mitigate the losses due to fall armyworm (FAW) infestation in maize, chemical pesticides had been the first choice and widely used as an emergency response. However, it comes with attendant health effect. This necessitates the development of plant based effective and safer pesticides. This research investigate response of fall armyworm larvae when they are exposed to crude and partially purified Tithonia diversifolia leaf extract.

Methods: Chemical constituent of the extract was identified using NIST08.LIB library spectra provided by the software on a GC-MS system and FTIR analysis was done using KBr pellet technique with a resolution and scanning speed of 4 cm^-1 and 2 mm/s. Dose dependent toxicity assay of T. diversifolia extracts on FAW at different growth stages under controlled environment in laboratory, followed by its effect under phytotron were examined against control and azadirachtin from neem.

Results: The GC-MS of the butanol eluent revealed 20 compounds out of which the major ones being beta-d-glucopyranoside, methyl (15.225 %) palmitic acid, TMS derivative (10.98 %) and hexadecanoic acid, 2-[(trimethylsily)oxy]-, methyl ester (8.75 %). The FT-IR spectroscopic analysis of the butanol eluent of T. diversifolia leaf extract revealed the presence of alcohols, phenols, aldehydes, ketones, alkanes and primary amines. The butanol eluent and crude extract caused 96 % mortality at neonate and first instar FAW larvae.

Conclusions: The toxic and repellant effects revealed by diet bioassay and phytotron experiment respectively suggest that butanol eluent of T. diversifolia leaf extract could be a good and effective target for biopesticide production against FAW.