TOXIC, ANTIFEEDANT AND REPELLENT ACTIVITY OF AQUEOUS CRUDE EXTRACTS OF Tephrosia vogelii HOOK ON THE LARVAL STAGES OF Helicoverpa armigera HÜBNER

Abstract

Laboratory bioassays were conducted to evaluate the bioactivity of aqueous crude extracts of Tephrosia vogelii Hook against

Helicoverpa armigera Hübner larvae. Fresh chickpea leaves, immersed in aqueous crude extracts of Tephrosia vogelii at

four rates (0, 5, 10 and 20% w/v), were assayed for toxic, antifeedant and repellent effects against 2nd and 3rd instar larvae of

1. armigera in a completely randomized design (CRD) with 3-5 replicates per treatment. Ordinary water and Dimethoate

(Rogor E40) ® at 2% v/v were included as negative and positive controls, respectively. Data on corrected percent mortality,

repellence and deterrence coefficient were first homogenized using angular transformations before being subjected to analysis

of variance (ANOVA) and means separated by Tukey’s HSD test. Results showed that the toxic, antifeedant and repellent

effects of crude aqueous extracts of T.vogelii against H. armigera larvae were significantly (P<0.0001) influenced by intra

plant variability, concentration applied, duration (hours) and corresponding factor interactions. At the highest concentration

of 20% w/v, the aqueous crude extracts obtained from the leaves (22%) and pods/flowers (av. 11%) of T.vogelii were weakly

toxic. In the antifeedant bioassay, leaf extracts caused the highest reduction (96%) in weight of larvae followed by pods/

flowers (79%) and succulent stems (2.5%), respectively. There were corresponding reductions in larval feeding as the

concentration of aqueous crude extracts increased. In the repellence test, except for leaf and pod/flower extracts at 20% w/v

and 1 h exposure that produced moderate percent repellence (41.67%) against the larvae, there was a dose- and exposure

time-dependent attraction of H. armigera larvae to chickpea leaves (food) treated with aqueous extracts of T. vogelii. The

plant offers hope as a potential cost-effective and environmentally benign antifeedant for H. armigera control in chickpea