Operational Key for Microscopical Identification of Fragments from EU-Authorized Insect Species in Feed

The microscopic identification of insect derived processed animal proteins (PAPs) is essential for feed control within the European Union, where light microscopy remains the official method for detecting prohibited animal proteins. This study synthesizes current morphological knowledge for the insect species authorized as feed materials Hermetia illucens, Musca domestica, Tenebrio molitor, Alphitobius diaperinus, Acheta domesticus, Gryllodes sigillatus, Gryllus assimilis and Bombyx mori and provides a comprehensive framework for their recognition in processed feed. Diagnostic traits were compiled from reference laboratory material, the scientific literature and the EURL AP micrograph collection, with emphasis on cuticular structures, setae, denticles, spiracles, tracheal elements, and species specific features such as spine like sensilla in H. illucens, gin trap structures in T. molitor, and distinctive antennal or cercal fragments in Orthoptera. Dipteran PAPs are characterized by unsclerotized cuticle, denticle bands, and spiracular morphology, whereas Coleopteran fragments display stronger sclerotization, larger mouthparts, and urogomphi. Orthopteran meals exhibit the greatest structural diversity due to the use of nymphs and adults, yielding leg, wing, antennal, and cercal fragments. Across taxa, tracheal and muscle fibre structures provide reliable confirmation of insect origin but lack species specificity. The study highlights persistent gaps in reference material, particularly for Musca domestica, and underscores the need for enhanced taxonomic training and the integration of automated image recognition tools and complementary molecular methods for species level confirmation. The identification key and morphological guidance presented here aim to support routine laboratory diagnostics and strengthen regulatory compliance in feed monitoring.