Whole-body imaging of Camponotus atrox using photoacoustic microscopy for three-dimensional morphological analysis: A preliminary study

Whole-body image analysis has been extensively applied in the field of entomology to identify differences in insect morphology. Although various conventional imaging techniques have been used for analyzing insect morphology, these often inflict damage on the sample during preparation and limitedly provide superficial information. To overcome the conventional limitations, in this study, we noninvasively observed the morphological structures of the ant Camponotus atrox, from the whole body to specific parts, over a wide scan range using optical-resolution photoacoustic microscopy (PAM). Based on the obtained photoacoustic maximum amplitude projection images, various structures of the ant, including the antenna, compound eyes, coxa, mandibles, mesonotum, propodeum, petiole, sting, and tergite, could be discerned by covering the entire ant body. In addition, we attained the morphological structures in detail by magnifying three specific parts, namely, the compound eyes, head, and thorax. Furthermore, we non-destructively analyzed the internal structure of various organs, such as the compound eyes, social stomach, and hindgut, via depth profiling of cross-sectional images. Finally, by implementing an algorithm, we visualized the depth-resolved en-face images of internal structures according to a constant depth interval. The findings established that the PAM system could identify not only each external morphological feature of the ant visible but also the sublayers of its internal structures. This study demonstrates the feasibility of PAM for contributing to performing morphological studies in entomological research.