## 4 Discussion
Although [PERSON] [35] and [PERSON] [36] have indicated the use of veratrine for thrips management, to our knowledge, this study is the first detailed evaluation of the repellency and toxicity of veratrine against WFT. Our results indicated that veratrine did not provide significant repellency at 0.05%. Fresh residue of veratrine also did not provide quick knockdown of WFT population, with the concentration of 0.5% achieving only 48% mortality after 72 h of exposure. Future insecticidal products should contain more than 0.5% veratrine in the mixed solution when it is used against WFT. Stemonine was the only novel plant compounds of interest to us that had demonstrated some level of repellency and toxicity against WFT. _Stemona_ spp., which contain more than 80 alkaloids, have a long history as medicinal and insecticidal plants in Asia [37; 38]. The majority of insecticidal products were extracted from the roots of _Stemona_ plants, demonstrating neurological, antifeedant and growth regulating activities [37; 38]. [PERSON] et al. [39] reported that Stanza, a botanical insecticide that contains extracts of _Stemona tuberosa_ Lour. root and pink plume poppy, reduced chilli thrips (_Scirotthorips dorsalis_ Hood) densities, but the active insecticidal alkaloid was not identified. In this study, plant extract containing stemonine demonstrated repellency at 0.05% (seconded to that of pyrethrins) in the two-choice (plant extract) bioassays but failed to repel WFT even at the concentration of 0.1% in the two-choice (concentrations) bioassays. It is not clear why the results from the two bioassays suggested different repelencies. Fresh 0.5% stemonine residue achieved 78% mortality at 72 h after exposure, but 1-d-old residue from 0.5% stemonine only achieved 33% mortality within the same exposure period. The comparison suggests rapid breakdown of stemonine residue under sunlight. Despite this rapid degradation, stemonine still achieved greater aged residual toxicity than other plant extracts where 7-d-old stemonine residue was the only one achieving 15% mortality after 72 h of exposure (<8% for other extracts). The inconsistency in the repellency and toxicity of stemonine warrants additional studies to evaluate its potential as a botanical insecticide. We suggest that future evaluations of the efficacy of stemonine against WFT should focus on identifying effective concentrations above 0.5%. Matrine and oxymetrine have been developed into commercial insecticides, and several studies had demonstrated their efficacies against various insect pests. Matrine applied at 0.5 to 1.5 mL/L achieved similar mortality and banana fruit damage by _Thrips hawaiensis_ Morgan as abamectin [40]. Oxymatrine or matrine had LC\({}_{50}\) values against adult and immature WFT that were comparable to those of fipronil and much higher than those of cypermethrin, diazinon and imidaloprid [12]. In our study, however, matrine was not effective against WFT. Matrine did not provide repellency against WFT in two-choice bioassays, and direct contact with fresh matrine residue resulted in 51% mortality after 72 h of exposure. Data from this study suggested that formulated product should require application at >0.5% matrine to achieve some level of reduction in WFT abundance and damage. The goal of our project was to identify plant extracts and active ingredients that can be further developed into effective insecticides or acaricides. Our results indicated that plant extracts containing celangulin, cnidium lactone, matrine and veratrine did not provide repellency and toxicity against WFT at a level generally considered acceptable or effective. Stemonine demonstrated repellency and toxicity, albeit at lower levels than nicotine, pyrethrins and rotenone. The efficacy of stemonine may be improved with higher application concentration (>0.5%) or frequency. Its crop safety (i.e., in reducing phototoxicity) and residual longevity needs to be improved with more refinement in extraction solvent and methods.