Morphology of the mouthparts of the yellow mealworm beetle Tenebrio molitor (L.) (Coleoptera: Tenebrionidae)

The yellow mealworm beetle, Tenebrio molitor (L.) (Coleoptera: Tenebrionidae), is known to be an important stored products pest, even though its larvae are considered one of the most common feed and food edible insect. We investigated the maxillo-labial complex morphology of the last instar larvae, using Electron Microscopy techniques. The maxillary palps are composed by three segments. On the second segment we observed two sensilla supposed to be mechanoreceptors, one dorsally and one externally located. On the third segment we found: a sensory complex composed by four different types of putative olfactory and gustative sensilla, located on the tip; up to four putative chemoreceptors and one putative mechanoreceptor located on the internal side; one digitiform sensilla, supposed to be hygroreceptor, located on the external side. The labial palps are composed by two segments. On the latero-ventral side of the second labial segment we found sensilla supposed to be gustative and on the tip we observed a sensory complex similar to the one described on the maxillary palp tip. The function of most of the sensilla was supposed by morphological similarities with sensilla in closely related insects. For this reason, further ultrastructure investigations are necessary to better describe and understand the function of each sensillum and their correlation with T. molitor food preference behavior