Evaluation of the mosquitocidal activity of <i>Photorhabdus</i> and <i>Xenorhabdus</i> extracts against the larvae of <i>Aedes aegypti</i> (Diptera: Culicidae)

Aedes aegypti is the main vector for dengue viruses. Alternative control of this mosquito was proposed because of its resistance to chemical insecticides. The symbiotic bacteria Photorhabdus associated with Heterorhabditid nematodes and Xenorhabdus associated with Steinernematid nematodes may be alternative resources for controlling this mosquito vector. Therefore, the present study evaluated extracts from Photorhabdus and Xenorhabdus bacteria against A. aegypti larvae. The larvicidal bioassay was performed according to the World Health Organization guidelines for laboratory and field testing of mosquito larvicides. Survival curves were analyzed to compare the mortality of the A. aegypti larvae between the ethyl acetate extracts and the control group. In addition, high-performance liquid chromatography-mass spectrometry analysis was performed to elucidate the natural compounds produced by these bacteria. Among 4 Photorhabdus isolates, the Photorhabdus luminescens subsp. hainanensis (bWT8.5_TH) extracts resulted in the greatest mortality (69%), whereas among 8 Xenorhabdus isolates, the Xenorhabdus stockiae (bWT8.5_TH) extracts resulted in the greatest larvicidal activity against A. aegypti, with 99% mortality after exposure to the 1% extracts for 96 hours. In contrast, at concentrations of 0.1, 0.01, and 0.001% of the extracts, no or less mortality of A. aegypti larvae was detected after exposure to the extracts for 24, 48, 72, and 96 hours. A natural compound, xenoamicine, is a common natural compound produced by Xenorhabdus bacteria. Therefore, extracts of Xenorhabdus and Photorhabdus bacteria may be used as biocontrol compounds for killing A. aegypti larvae.