Anti-feedant activity of selected botanical extracts and their combinations on Plutella xylostella larvae

Many insect pests including the diamondback moth (Plutella xylostella L.) which has a known history of developing resistance to many pesticides, are believed to be able to develop that resistance as a result of a continuous and repeated use of pesticides with similar modes of action and or active ingredients. In nature however, plants would have been extinct; but plants produce compounds with toxicity to a wide variety of potential herbivores (Bush et al., 1997). Plants under attack release a cocktail of volatile compounds that act as cues for these allies, which then attack, consume and reduce the populations of herbivores (De Moraes et al., 1998). The aim of this study was to evaluate and compare the feeding and anti-feeding effects of Azadirachta indica, Chrysanthemum cinerariifolium and Quassia amara extracts (Azadirachtin, Pyrethrin and Quassin, respectively) and their mixtures on diamondback moth larvae. Larvae were fed with cabbage leaf disks treated with the various extracts. Mortality and leaf area consumed by larvae were recorded after 24 h of larval exposure to the treated leaves. Results revealed varying level of feeding and anti-feedant effects among all the formulations. Formulations with the highest concentration resulted in an increased feeding and anti-feedant effect in terms of larval mortality and feeding area. The most effective anti-feedant effect was recorded by the Pyrethrin, and Azadirachtin + Pyrethrin mixture (with a 1.0% feeding area each), followed by Azadirachtin + Pyrethrin + Quassin mixture and Pyrethrin + Quassin mixture with 2 and 3% feeding area, respectively. Pyrethrin, Azadirachtin + Pyrethrin and Azadirachtin + Pyrethrin + Quassin extracts combinations on the other hand recorded 50, 40 and 50% total larval mortality, respectively.