## 4 Discussion  
Plant secondary metabolites represent a rich source of medicinal and pest management compounds. Several plant extracts tested in this study contain compounds that have demonstrated antioxidant, antimicrobial, anticancer and other medicinal properties [16; 17; 18]. Some have been tested for their insecticidal and acaricidal properties, whereas others (e.g., matrine, nicotine, pyrethrins and rotenone) were previously or are still available as formulated insecticides or acaricides. Celangulin is extracted from the Chinese bittersweet, _C. angulatus_, which has traditionally been used as an insecticidal plant in China [19]. Proposed modes of action of celangulin include disruptions of normal membrane potential in midgut and signaling pathway in neuron [20; 21; 22; 23; 24; 25; 26]. The majority of studies have examined the efficacy of celangulin against lepidopteran larvae [21; 22; 23; 24; 25; 26] and coleopteran adults [27]. This study represents the first attempt to evaluate the insecticidal activity of celangulin against WFT. Our results suggested that celangulin did not provide repellency against WFT at the concentration of 0.05% and did not provide sufficient contact toxicity against WFT at concentrations ranging from 0.01 to 0.5%. The maximum percent mortality was <20% when WFT were in contact with fresh residue. Formulated products containing 0.15% to 0.2% celangulin have purportedly been \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Active Ingredient**} & \multirow{2}{*}{**Residual Age (Days)**} & \multicolumn{3}{c}{**Mean Percent Mortality 1 at**} \\ \cline{3-5}  & & **24 h** & **48 h** & **72 h** \\ \hline \multirow{3}{*}{Nicotine (at 0.1\%)} & 1 & 15.1 \(\pm\) 3.5 a & 22.2 \(\pm\) 6.9 a & 25.9 \(\pm\) 5.9 a \\  & 3 & 4.0 \(\pm\) 0.2 b & 4.0 \(\pm\) 0.2 b & 6.0 \(\pm\) 0.2 b \\  & 5 & 0 b & 10.1 \(\pm\) 5.8 ab & 10.1 \(\pm\) 5.8 b \\  & 7 & 2.2 \(\pm\) 2.2 b & 2.2 \(\pm\) 2.2 b & 6.2 \(\pm\) 2.6 b \\ \hline \multirow{3}{*}{Pyrethrins (at 0.05\%)} & 1 & 18.5 \(\pm\) 4.1 a & 21.9 \(\pm\) 4.1 a & 22.1 \(\pm\) 4.0 a \\  & 3 & 2.0 \(\pm\) 2.0 b & 2.0 \(\pm\) 2.0 b & 2.0 \(\pm\) 2.0 b \\  & 5 & 0 b & 0 b & 0 b \\  & 7 & 2.5 \(\pm\) 2.5 b & 2.5 \(\pm\) 2.5 b & 2.5 \(\pm\) 2.5 b \\ \hline \multirow{3}{*}{Rotenone (at 0.1\%)} & 1 & 18.5 \(\pm\) 4.1 a & 20.2 \(\pm\) 3.7 a & 24.0 \(\pm\) 3.3 a \\  & 3 & 2.5 \(\pm\) 2.5 b & 2.5 \(\pm\) 2.5 b & 2.5 \(\pm\) 2.5 b \\  & 5 & 0 b & 2.5 \(\pm\) 2.5 b & 5.0 \(\pm\) 5.0 b \\  & 7 & 2.5 \(\pm\) 2.5 b & 2.5 \(\pm\) 2.5 b & 7.5 \(\pm\) 2.5 b \\ \hline \multirow{3}{*}{Stemonine (at 0.5\%)} & 1 & 13.4 \(\pm\) 2.1 & 28.8 \(\pm\) 3.2 a & 32.7 \(\pm\) 6.8 \\  & 3 & 10.0 \(\pm\) 2.6 & 20.9 \(\pm\) 5.9 a & 24.4 \(\pm\) 6.8 \\ \cline{1-1}  & 5 & 10.0 \(\pm\) 4.1 & 15.4 \(\pm\) 2.8 ab & 17.7 \(\pm\) 7.6 \\ \cline{1-1}  & 7 & 6.7 \(\pm\) 3.4 & 6.7 \(\pm\) 3.4 b & 15.4 \(\pm\) 5.1 \\ \hline \hline \end{tabular} 1  
\end{table} 
Table 5: Mean Abbott-corrected percent mortality (\(\pm\) SEM) of western flower thrips adults exposed to periwinkle flowers with residue of various ages after the plants were sprayed with various plant extract and Tween 20 solutions in the aged residue toxicity bioassays. developed [19]. Our study indicated that celangulin formulated at these concentrations is not likely to be effective against WFT. Veratrine has been documented as a voltage-gated sodium channel activator in rat [28] and a dose-dependent, non-competitive inhibitor of acetylcholinesterase in Drosophila [29]. The insecticidal activity of sabadilla seed powder has been known since the 16 th century [30]. Veratrine, the most toxic of sabadilla alkaloids [30], has being studied as an insecticide in the 1940s [31; 32; 33]. Since then, few scientific evaluations of the efficacy of veratrine as an insecticide have been published. [PERSON] et al. [34] reported that all _Euxoa messoria_ (Harris) (Lepidoptera: Nocutiade) first instars died within a week of being offered diet containing veratrine.