Mouthparts of the bark beetle (Ips acuminatus) as a possible carrier of pathogenic microorganisms

• We observe cuticular microstructure of the mouthparts in Ips acuminatus.
• Mouthparts exhibit typical morphology of chewing type of mycophagous coleoptera.
• Microorganisms were concentrated at the cuticular grooves of the mouthparts where cuticular hairs are densely packed.
• Cuticular surface of the maxillary and labial palpi provides sufficient spaces to accommodate yeast-like spores.
• Implication ability of mouthparts to act as a mechanical carrier of pathogen is discussed.

The bark beetle Ips acuminatus Gyllenhal (Coleoptera: Curculionidae: Scolytinae) has been recently reported as one of the most serious secondary pests of pine trees. Since the adult beetles chew the sapwood to create tunnels, they have developed effective drilling mouthparts enough to make galleries directly into the heartwood of the tree. The mouthparts of this bark beetle exhibit typical morphology of mycophagous coleopteran beetles and have those characteristics of chewing mouthparts. Both maxillary and labial palpi have the functions of directing the food to the mouth and holding it while the mandibles chew the food. Although this bark beetle did not have prothoracic mycangial cavities, yeast-like spores were concentrated at the invaginated surface of mouthparts where cuticular hairs are densely packed. In particular, the cuticular surface around the base segments of these palpi has sufficient spaces to accommodate microorganisms during the series of drilling or feeding processes. Therefore, this paper reports detailed observation of the cuticular structure of the mouthpart using the field emission scanning electron microscopy (FESEM) for the purpose of demonstrating its possible implication to act as external carriers of pathogenic microorganisms.

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