Evaluation of insecticidal and repellency activity of leaf extracts of Andrographis paniculata against Tribolium castaneum (red flour beetle)

Abstract

The desire for developing alternative natural pesticides/ repellents for pests causing crop loss, is growing each year, as the harmful effects of synthetic pesticides on humans and non-target species become established. Plants being the age-old source of various bioactive compounds, the insecticidal and repellency potential of Andrographis paniculata leaves was evaluated against adults of major stored-grain insect, Tribolium castaneum. Diet preference and dosage-mortality were the basis of assays to determine the repellency and insecticidal potential of the five solvent extracts i.e petroleum ether, ethyl acetate, acetone, 2-propanol, and water. Repellency assay was performed by evaluating the number of adult insects that preferred areas of localization between extract treated portion and control portion, on a filter paper disc. Statistical comparative analysis of averaged repellency and mortality rate was estimated with respect to increasing concentration (2.5%, 5%, and 10%) and duration of exposure (6 h interval). Our findings align with the facts that increase in the duration of exposure and concentration of solvent extracts increases the mortality of T. castaneum. The iso-propanolic extract showed complete repellency (within 12 h) and lethality (83%) on the insect and also significant activity was observed in the aqueous extract. The observed value of lethal dose (50%) for the iso-propanolic extract with 15 days of exposure was 26.6 mg/g and that of lethal time (LT50) is eight days. The present study supported the occurrence of insect-specific antagonistic bioactive compounds in A. paniculata and depicted favored choice of solvents for the extraction of insecticidal constituents. It also underpins its potential as an alternative source of natural compounds for the management of stored grain pest.