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<p><i>Spiroplasma</i>, a bacterium that infects some insects, is known to induce male-specific mortality in its hosts. It has been identified in the spongy moth (<i>Lymantria dispar japonica</i>), but it remains unclear whether it causes male mortality in this host. Therefore, in this study, we collected 271 spongy moth egg masses from 27 locations in Japan to identify <i>Spiroplasma</i>-infected egg masses. Using 16S rRNA-targeted PCR, 27 of the 271 egg masses were <i>Spiroplasma</i>-positive. Most of these egg masses originated from <i>L. umbrosa</i>, whereas only three originated from <i>L. dispar japonica</i>. Phylogenetic analysis revealed that the detected <i>Spiroplasma</i> belonged to the <i>Spiroplasma ixodetis</i> clade and was identical to previously reported strains derived from <i>L. dispar japonica</i>. Bacterial density varied significantly among egg masses, and we observed a tendency toward higher vertical transmission efficiency when the maternal bacterial density was high. As development progressed, bacterial density increased, reaching approximately 50–150 cells/host cell in the Malpighian tubules at the pre-pupal stage. Nevertheless, no female-biased sex ratio was observed; thus, no notable male-killing effect was confirmed. To our knowledge, this is the first study to report <i>Spiroplasma</i> infection in <i>L. umbrosa</i>. Our findings strongly suggest that the identified <i>Spiroplasma</i> species is a non-male-killing type.</p>

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Large-scale field sampling reveals non-male killing Spiroplasma infection in Lymantria umbrosa in Hokkaido, Japan

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  • 发表日期：

    2026年5月28日

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  • Kyoko Ishida,
  • Maki N. Inoue,
  • Masataka G. Suzuki

摘要

Spiroplasma, a bacterium that infects some insects, is known to induce male-specific mortality in its hosts. It has been identified in the spongy moth (Lymantria dispar japonica), but it remains unclear whether it causes male mortality in this host. Therefore, in this study, we collected 271 spongy moth egg masses from 27 locations in Japan to identify Spiroplasma-infected egg masses. Using 16S rRNA-targeted PCR, 27 of the 271 egg masses were Spiroplasma-positive. Most of these egg masses originated from L. umbrosa, whereas only three originated from L. dispar japonica. Phylogenetic analysis revealed that the detected Spiroplasma belonged to the Spiroplasma ixodetis clade and was identical to previously reported strains derived from L. dispar japonica. Bacterial density varied significantly among egg masses, and we observed a tendency toward higher vertical transmission efficiency when the maternal bacterial density was high. As development progressed, bacterial density increased, reaching approximately 50–150 cells/host cell in the Malpighian tubules at the pre-pupal stage. Nevertheless, no female-biased sex ratio was observed; thus, no notable male-killing effect was confirmed. To our knowledge, this is the first study to report Spiroplasma infection in L. umbrosa. Our findings strongly suggest that the identified Spiroplasma species is a non-male-killing type.