## 1 Introduction  
Botanical pesticides have long been utilized in arthropod pest management [1, 2]. Pyrethrum was used as early as 400 B.C., and commercial products containing nicotine and rotenone were available for pest management since the 17 th and 19 th centuries, respectively. Azadirachtin was first isolated in 1968 and has since become one of the most widely available and utilized botanical pesticides in the world [3]. Although their importance was largely eclipsed by synthetic pesticides since the mid-20 th century, botanical pesticides are enjoying resurgence in popularity because of a renaissance in sustainable and organic agriculture, and ever-increasing concerns over the costs, accessibility, resistance development and environmental impacts of synthetic pesticides [4].  
Botanical pesticides currently available in the world's marketplaces are mainly essential oils and raw or refined plant extracts containing secondary metabolites such as flavonoids, terpenoids and phenylpropanoids [2, 4, 5]. Active ingredients in these botanical insecticides exhibit a range of biological activities, including repellency, neurotoxicity, and inhibition of feeding, growth and reproduction [5, 6]. The exact modes of action of these active ingredients are not well understood. Some compounds serve as the progenitors of synthetic pesticides, with the same modes of action [7]. For example, pyrethrins have the same mode of action as pyrethroids, which are sodium channel modulators. Nicotine and neonicotinoids share the same mode of action, which are nicotinic acetylcholine receptor competitive modulators. Other commercialized botanical active ingredients appear to target different processes and proteins within arthropod nervous systems [5].  
While numerous studies have investigated the biological activities and efficacies of botanical insecticides, only a limited number have been conducted with the western flower thrips (WFT), _Franklinella occidentalis_ Pergande (Thysanoptera: Thripidae), one of the most widely distributed and economically important pests and vectors of tospoviruses in the world. JP503 [an extract of _Perilla frutescens_ var. _crispa_ (Thumb.) [PERSON]; Lamiaceae) caused 100% mortality in a WFT population within 3 h of a leaf dip [8]. Oil and raw extracts from _Azadinchitta indica_ A. Juss (Meliaceae) and _Datura alba_ (Nees) (Solanaceae) caused more than 40% mortality in a WFT population within 48 h [9]. [PERSON] et al. [10] reported optimal control of a WFT population with a homemade extract of garlic, onion and pepper. Pyrethrins reduced WFT feeding and survival [11]. Oxymatrine or matrine, extracted from the roots of _Sophora flavescens_ Aiton (Fabaceae), was slow in killing WFT [12]. UDA-245, an essential oil extract of _Chenopodium ambrosoides_ L. (Amaranthaceae), applied at 1% was found to be the only product that had provided suppression of a WFT population at 2 weeks after treatment [13].  
New plant-derived active ingredients are frequently being identified and introduced for pharmaceutical and pesticidal uses. The spectrum of insecticidal activity and efficacy of these new active ingredients should be evaluated to assess their potential for incorporation into existing pest management programs to enhance insecticide efficacy or delay insecticide resistance development. We investigated the efficacy of four plant extracts (containing clengulin, cnidium lactone, stemonine and veratrine) against WFT, and compared their efficacies to plant extracts with known activity against thrips (matrine, nicotine, pyrethrins and rotenone). We first evaluated their repellency against WFT in laboratory bioassays. We then evaluated their residual toxicities against WFT in laboratory and greenhouse bioassays. Our goal was to identify novel plant extracts that are more repellent and toxic to WFT than the currently known or available botanical insecticides.