Synergistic Effects of Rotenone and Abamectin on Physiological Suppression, Population Inhibition, and Ion Disruption of Bursaphelenchus xylophilus

Pine wilt disease, which is induced by pine wood nematode (PWN, <i>Bursaphelenchus xylophilus</i>), has caused huge economic and ecological losses. To overcome the drawbacks of chemical control against PWN, twenty compounds were screened, and a synergistic botanical-chemical combination was identified. A proportion of abamectin to rotenone of 7:3 (5.73 and 1.78 mg/L, respectively) achieved the highest co-toxicity coefficient of 231.09 with a median lethal concentration of 3.18 mg/L. It revealed 0% mortality in <i>Pinus massoniana</i> seedlings at 60 days post-treatment when applied at 400 times the synergistic concentration (2.29 g/L abamectin + 0.71 g/L rotenone) at 7 days after PWN inoculation. Furthermore, the synergistic combination significantly affected the physiological activity and population dynamics of PWN. Female oviposition was reduced by 71.92%, the egg hatching rates declined to 13.09 ± 0.02%, and head thrashing frequency was inhibited by 99.23 ± 0.01%. The enzymatic activities of peroxidase, acetylcholinesterase, succinate dehydrogenase, and glutathione S-transferase were significantly increased, while the population size declined by 96.17%. Transcriptomic and gene expression analyses suggested a potential "Na⁺/Ca²⁺/Cl^- ionic storm," since the synergistic combination significantly activated genes associated with voltage-gated calcium channels, glutamate-gated chloride channels, and amiloride-sensitive sodium channels. These findings provide an eco-friendly strategy for PWN management via chemical control.