Bioactivity of Ageratum conyzoides (L.) (Asteraceae) on feeding and oviposition behaviour of diamondback moth Plutella xylostella (L.) (Lepidoptera: Plutellidae)

Abstract

Effects of foliage extracts of goat weed, Ageratum conyzoides (Family: Asteraceae) on feeding, oviposition and egg hatchability of diamondback moth, Plutella xylostella were assessed under standard laboratory conditions. Bioassays using aqueous, methanol and hexane crude extracts were conducted in no-choice and choice conditions. The larval feeding on 0.5% hexane extract treated leaf surface reduced to more than half relative to control in the choice condition; however, complete inhibition of feeding was recorded at 2% and higher concentration of extract. In no-choice bioassays, the larval feeding consistently decreased with increasing concentration of the hexane extract. Larval feeding on methanol extract treated leaves was also significantly reduced, although in the concentration dependent manner in both choice and no-choice bioassays. Likewise, the aqueous extract also reduced larval feeding at 3%, 4% and 5% concentrations of extracts in both no-choice and choice bioassays. The Antifeedant Index (AFI) for hexane extract was 100 at 2% concentration, while AFI values were 78.4 and 41.5 for 5% concentration of methanol and aqueous extracts, respectively. The egg laying on the leaf surface treated with hexane and methanol extracts was significantly reduced in the concentration dependent manner, as compared to the control in both choice and no-choice bioassays. However, the aqueous extract did not affect egg laying. The egg hatchability was completely inhibited at higher concentrations of the hexane extract, but not at any concentration of the methanol and aqueous extracts. The oviposition Deterrent Index values for the hexane and methanol extracts were statistically similar, however. These results indicate that the crude hexane and methanol extracts of A. conyzoides foliage could potentially be used for the management of diamondback moth.