Abstract :
In the search for biopesticides, increasing attempts have been made to obtain bioactive compounds from plants. In this regard, the insecticidal activity and deterrence of saponins obtained from Yucca schidigera Roezl(Agavaceae) were tested on the major stored product pest, Tribolium castaneum (Herbst) (Coleoptera :Tenebrionidae) via feeding bioassay. Adult beetles were reared on wheat grain dusted with saponins at 1 to 5% concentrations (wt/wt) for 1 to 14 days under optimal development conditions. Our results indicated that the increase of concentration and exposure periods enhanced mortality. The mortality reached 81 and 94% at 1 and 5% saponins, respectively, after 14d of exposure. In the choice test with treated and untreated grains, yucca saponins were able to deter adults immediately after the first 2hr up to the end of the exposure interval after 24hr at 1 and 5% concentrations. The respective deterrent indices were (0.43 - 0.55) and (0.52- 0.78) at the tested intervals. In addition, cellular immune reactions were recorded in adult females as shown by changes in the differential hemocyte counts (DHCs) following the challenge with yucca saponins for 72hr. Finally, the application of yucca saponins at 1 and 5% extensively reduced the grain damage potential by 70 and 80%, respectively, after 7d of application while the reduction increased after 14 d to 73% and 85%, respectively. Due to the combined contact, toxicant and deterrent properties of yucca saponins, they could be considered as a potentially applicable grain protectant against T. castaneum.
Keyword :
Deterrence, Survival, Tribolium castaneum, Yucca saponins, immune response