Quantitative color profiling method using digital images to determine the phenotypic relationships of beetles in selected urban areas of Southern Philippines

Natural Sciences Department, College of Arts and Sciences, University of Southeastern Philippines, Barrio Obrero, Davao City, Philippines

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Abstract

The assessment and comparison of colors have historically relied on subjective methods, which may introduce potential inaccuracies specially comparing diverse coloration of insects such as beetles. In contrast, modern objective techniques frequently require expensive equipment and specialized knowledge. This study utilized beetle images to quantify their color patterns and assess phenotypic relationships among species. Beetle specimens were collected from selected urban regions in Southern Philippines, using opportunistic sampling. The specimens were then preserved in 70% ethyl alcohol and subsequently dissected. Under precisely controlled conditions, the elytron of 48 insects was photographed. The color values of the images were extracted and converted to Commission on Illumination, 1976 L*a*b* (CIELab) color space after calibration. Using cluster analysis, the color distance of the elytron images was compared across samples. Results showed that the average elytral coloration displays moderate darkness, a subtle reddish hue, and an appreciable infusion of yellowness. Furthermore, colorimetric analysis showed that elytron of sampled beetles displays two distinct color variations: (1) a moderate luminosity characterized by prominent reddish hues and evident yellow manifestation, and (2) a darker version with a subtle reddish undertone and faint yellow hints. The findings of this investigation showed potential use of digital images in objectively assess color patterns of beetles in urban environments.