Essential Oil Compositions of Three Invasive Conyza Species Collected in Vietnam and Their Larvicidal Activities against Aedes aegypti , Aedes albopictus , and Culex quinquefasciatus

Mosquito-borne infectious diseases are a persistent problem in tropical regions of the world, including Southeast Asia. Vector control has relied principally on synthetic insecticides, but these have detrimental environmental effects and there is an increasing demand for plant-based agents to control insect pests. Invasive weedy plant species may be able to serve as readily available sources of essential oils, some of which may be useful as larvicidal agents for control of mosquito populations. We hypothesize that members of the genus (Asteraceae) may produce essential oils that may have mosquito larvicidal properties. The essential oils from the aerial parts of , , and were obtained by hydrodistillation, analyzed by gas chromatography-mass spectrometry, and screened for mosquito larvicidal activity against , and . The essential oils of and , both rich in limonene (41.5% and 25.5%, respectively), showed notable larvicidal activities against (24-h LC = 9.80 and 21.7 μg/mL, respectively) and (24-h LC = 18.0 and 19.1 μg/mL, respectively). These two species may, therefore, serve as sources for alternative, environmentally-benign larvicidal control agents.