Sensory structures on maxillary and labial palps of Tenebrio molitor

The yellow mealworm beetle Tenebrio molitor L. (Coleoptera Tenebrionidae) is an important stored products pest, although its larvae are also one of the most promising for food and feed. Although T. molitor has been widely investigated, there remains a lack of information about the sensory structures on maxillary and labial palps. Here, it was investigated the external morphology and distribution pattern of the sensilla on mouthpart palps of T. molitor larvae using scanning electron microscopy. In T. molitor, the maxillary palp has three segments, whereas the labial palp has two segments. Based on the morphology of the features of the sensilla on the apical articles of both the maxillary and labial palps, we classified them into nine types: sensilla trichoidea types 1 and 2, sensilla digitiformia, sensilla chaetica, sensilla coeloconica, sensilla basiconica types 1 and 2, sensilla styloconica types 1 and 2. A total of 23 sensilla on maxillary palps and 13 sensilla on labial palps were found. In particular, the sensilla basiconica form the sensory complex located on the tip of each palp. In T. molitor, the numbers of sensilla present on the sensory complexes do not differ between maxillary and labial palps, as 13 units.