The phytohormone production hypothesis suggests that organisms, including insects, induce galls by producing and secreting plant growth hormones. Auxins and cytokinins are classes of phytohormones that induce cell growth and cell division, which could contribute to the plant tissue proliferation which constitutes the covering gall. Bacteria, symbiotic with insects, may also play a part in gall induction by insects through the synthesis of phytohormones or other effectors. Past studies have shown that concentrations of cytokinins and auxins in gall-inducing insects are higher than in their host plants. However, these analyses have involved whole-body extractions. Using immunolocalization of cytokinin and auxin, in the gall-inducing stage of Eurosta solidaginis, we found both phytohormones to localize almost exclusively to the salivary glands. Co-localization of phytohormone label with a nucleic acid stain in the salivary glands revealed the absence of Wolbachia sp., the bacterial symbiont of E. solidaginis, which suggests that phytohormone production is symbiont independent. Our findings are consistent with the hypothesis that phytohormones are synthesized in and secreted from the salivary glands of E. solidaginis into host-plant tissues for the purpose of manipulating the host plant.

植物激素产生假说表明，包括昆虫在内的生物体通过产生和分泌植物生长激素来诱发虫瘿。生长素和细胞分裂素是诱导细胞生长和细胞分裂的植物激素，有助于构成覆盖瘿的植物组织增殖。与昆虫共生的细菌也可能通过合成植物激素或其他效应物在昆虫的虫瘿诱导中发挥作用。过去的研究表明，胆诱导昆虫中细胞分裂素和生长素的浓度高于其寄主植物。然而，这些分析涉及全身提取。使用细胞分裂素和生长素的免疫定位，在欧洲一枝黄线虫的胆诱导阶段，我们发现这两种植物激素几乎完全定位于唾液腺。植物激素标记与唾液腺中核酸染色剂的共定位表明，不存在沃尔巴克氏菌（E. Solidaginis的细菌共生体） ，这表明植物激素的产生是不依赖于共生体的。我们的研究结果与以下假设一致：植物激素是在实体瘤唾液腺中合成并分泌到宿主植物组织中，以操纵宿主植物的。