Abstract
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.
Highlights
Age determination of beetle larvae is a difficult task [1]
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
We conclude that larval instar classifiers of the subfamily or genus level have very high classification accuracy and they may be safely used to classify carrion beetle larvae according to instar in forensic practice
Summary
Age determination of beetle larvae is a difficult task [1]. It can be estimated from length, weight, or developmental stage [2,3,4]. Measurements of larvae were found to be useful for this purpose and several quantitative features were proposed for the Palaearctic species Necrodes littoralis, Creophilus maxillosus (Linnaeus, 1758) [7], and Sciodrepoides watsoni (Spence, 1815) [8], a Neotropical species Oxelytrum discicolle (Brulle, 1840) [1], and the Nearctic species Necrodes surinamensis (Fabricius, 1775), Necrophila americana (Linnaeus, 1758), and Oiceoptoma inaequale (Fabricius, 1781) [9] This approach is based mainly on the ranges of features characteristic of particular instars [1, 8, 9]. Linear discriminant analysis was used to generate classification functions, on the basis of which larval specimens may be classified according to instar from measurements of just two features [7]
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