Abstract
Morphological shapes of the larval clypei of seven Cybister diving beetles (Coleoptera: Dytiscidae) from Japan—namely C. brevis Aubé, 1838; C. chinensis Motschulsky, 1854; C. lewisianus Sharp, 1873; C. limbatus (Fabricius, 1775); C. rugosus (Macleay, 1825); C. tripunctatus lateralis (Fabricius, 1798); and C. sugillatus Erichson, 1834—were investigated using landmark-based geometric morphometrics (GM). Younger instar larvae possess clypei with smaller centroid sizes than older larvae in all species. Distinct morphological changes in clypeus are also observed during larval growth. Canonical variate (CV) analysis indicated that CV1 (53.5%) has the most contributing factor explaining shape variations representing clypeus length from anterior to posterior margin. Younger larvae have longer clypei than older ones in all species. Leave-one-out cross-validation indicates that larval clypeus morphology can identify species with greater than 90% accuracy. According to cluster analysis, clypeus shape can also categorize the same species with 99.8% for the first instar larvae and 100% accuracy for the second and third instars. Thus, the GM method can accurately identify species and developmental stages of larvae among the seven Cybister species.
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