Study on Secondary Metabolites of Spodoptera litura Gut-Associated Bacteria and Their Induction of Tomato Resistance to Pests

Previous studies have found that the fermentation broth of gut-associated bacteria of the Spodoptera litura can induce resistance in tomatoes to the Spodoptera litura larva. In this paper, column chromatography and modern spectrometry techniques were utilised to isolate and identify the fermentation broth of gut-associated bacteria of Spodoptera litura, and five compounds were obtained, which were N-acetyltyramine (1), p-hydroxybenzeneacetic acid methyl ester (2), p-hydroxybenzenepropionic acid (3), 3-indolylcarboxaldehyde (4), and p-hydroxybenzeneethanol (5). These compounds were evaluated for their ability to induce insect resistance in tomato, revealing that all five increased the resistance of tomato to the Spodoptera litura to varying degrees. The strongest induced resistance was observed in tomatoes treated with compound 1 at 0.1 μg/mL, showing a 55.73% body weight inhibition against the Spodoptera litura. Compound 4, at 1 μg/mL, induced a 42.39% inhibition of larval weight. Compound 5 at 0.1 μg/mL induced a 42.39% inhibition of growth in tomato against Spodoptera litura as well. Compounds 2 and 3 at 1 μg/mL resulted in 30.20% and 39.66% inhibition of the weight growth of tomato against Spodoptera litura, respectively. Among them, the induction of compound 2 at 0.1 μg/mL even significantly promoted the feeding on tomato leaves by the Spodoptera litura.