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<p>Conifer phloem is typically nitrogen-poor, constraining the development of phloeophagous bark beetles and the growth of their microbial associates. Mountain pine beetle (<i>Dendroctonus ponderosae</i> Hopkins 1902) galleries contain ophiostomatoid fungi that can supplement insect nutrition, yet these fungi are also consumed by abundant mycetophagous mites. Whether such mites function solely as exploitative consumers or also return nitrogen to fungi through a recycling feedback loop remains unclear. We tested whether a common gallery mite, <i>Histiogaster arborsignis</i> Woodring 1963; the most abundant mycetophagous mite in the mountain pine beetle system, recycles nitrogen to a representative beetle-associated fungus, <i>Ophiostoma montium</i> (Rumbold) von Arx 1952. First, we compared fungal biomass responses to two nitrogen sources, homogenized dead mites and potato infusion, using ergosterol concentration as a proxy. Second, we conducted a two-stage <sup>15</sup>N tracer assay in which mites fed on <sup>15</sup>N-labeled fungal tissue. Mite carcasses and fecal pellets were collected and analyzed for <sup>15</sup>N enrichment. In the second stage, a subset of ¹⁵N-labeled dead mites was incorporated into fresh medium. Unlabeled fungal plugs were then placed onto the amended plates to establish secondary cultures. Isotope analyses showed that mites acquired fungal <sup>15</sup>N and that secondary cultures incorporated <sup>15</sup>N following exposure to mite-derived material. Together, these results indicate evidence of bidirectional nitrogen transfer between mites and fungi under experimental conditions. This interaction represents a localized recycling pathway that may influence nitrogen retention within beetle-fungus-mite communities, although its ecological consequences for beetles remain uncertain.</p>

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A fungal-mite nitrogen loop supports fungal symbionts in nutrient-poor host plant systems

  • 期刊论文

  • 发表日期：

    2026年5月9日

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  • Faizan Naeem,
  • Chance Park,
  • Ateeq Shah,
  • Lien T. Luong,
  • Nadir Erbilgin

摘要

Conifer phloem is typically nitrogen-poor, constraining the development of phloeophagous bark beetles and the growth of their microbial associates. Mountain pine beetle (Dendroctonus ponderosae Hopkins 1902) galleries contain ophiostomatoid fungi that can supplement insect nutrition, yet these fungi are also consumed by abundant mycetophagous mites. Whether such mites function solely as exploitative consumers or also return nitrogen to fungi through a recycling feedback loop remains unclear. We tested whether a common gallery mite, Histiogaster arborsignis Woodring 1963; the most abundant mycetophagous mite in the mountain pine beetle system, recycles nitrogen to a representative beetle-associated fungus, Ophiostoma montium (Rumbold) von Arx 1952. First, we compared fungal biomass responses to two nitrogen sources, homogenized dead mites and potato infusion, using ergosterol concentration as a proxy. Second, we conducted a two-stage 15N tracer assay in which mites fed on 15N-labeled fungal tissue. Mite carcasses and fecal pellets were collected and analyzed for 15N enrichment. In the second stage, a subset of ¹⁵N-labeled dead mites was incorporated into fresh medium. Unlabeled fungal plugs were then placed onto the amended plates to establish secondary cultures. Isotope analyses showed that mites acquired fungal 15N and that secondary cultures incorporated 15N following exposure to mite-derived material. Together, these results indicate evidence of bidirectional nitrogen transfer between mites and fungi under experimental conditions. This interaction represents a localized recycling pathway that may influence nitrogen retention within beetle-fungus-mite communities, although its ecological consequences for beetles remain uncertain.