Classification of forensically-relevant larvae according to instar in a closely related species of carrion beetles (Coleoptera: Silphidae: Silphinae)

Carrion beetle larvae of Necrodes littoralis (Linnaeus, 1758), Oiceoptoma thoracicum (Linnaeus, 1758), Thanatophilus sinuatus (Fabricius, 1775), and Thanatophilus rugosus (Linnaeus, 1758) (Silphidae: Silphinae) were studied to test the concept that a classifier of the subfamily level may be successfully used to classify larvae according to instar. Classifiers were created and validated using a linear discriminant analysis (LDA). LDA generates classification functions which are used to calculate classification values for tested specimens. The largest value indicates the larval instar to which the specimen should be assigned. Distance between dorsal stemmata and width of the pronotum were used as classification features. The classifier correctly classified larvae of N. littoralis and O. thoracicum, whereas in the case of T. sinuatus and T. rugosus a few misclassifications were recorded. For this reason, a separate genus level classifier was created for larvae of Thanatophilus. We conclude that larval instar classifiers of the subfamily or genus level have very high classification accuracy and therefore they may be safely used to classify carrion beetle larvae according to instar in forensic practice.