Honeydew-Associated Bacteria Suppress Zucchini Defense Responses and Enhance the Performance of the Cotton-Melon Aphid.

Aphid honeydew is generally regarded as a sugar-rich excretion, but it also contains microbial communities that may influence plant-herbivore interactions. Whether honeydew-associated bacteria suppress plant defense responses to enhance aphid performance remains unclear. Here, we investigated the effects of honeydew-associated bacteria from the cotton-melon aphid, Aphis gossypii, on defense responses in zucchini (Cucurbita pepo) and subsequent aphid performance. Compared with sterilized honeydew, crude honeydew significantly increased aphid body weight, suggesting that honeydew-associated bacteria contribute to enhanced aphid performance. This effect was associated with attenuation of multiple jasmonic acid (JA)- and salicylic acid (SA)-associated defense responses, including reduced expression of several defense-related genes, lower accumulation of free JA and free SA, and reduced PPO activity. Further assays with individual bacterial isolates showed that Mammaliicoccus sp. and Pseudomonas sp. significantly increased aphid body weight, whereas bacterial effects on JA- and SA-related gene expression and PPO activity were isolate- and time-dependent. Together, these results show that honeydew-associated bacteria can suppress zucchini defense responses and enhance the performance of A. gossypii. Our findings reveal honeydew microbiota as microbial modulators of plant-aphid interactions.