Fig. 1

Distribution and morphology of selected external sensilla in T. castaneum larvae. Scanning electron micrographs (SEMs) of ESO morphology and distribution in the 1st larval stage (a–i), and morphology of sensilla in the 2nd larval stage (j). Anterior is towards the left in a–k. a Whole larva: asterisks, position of tracheal pits; ant, antenna; h, head; t1–t3, thoracic segments 1–3; l1–l3, walking legs 1–3; a1–a8, abdominal segments 1–8; u, urogomphi; p, pygopods. b High magnification of head (ventral view) showing mouthparts: lb, labrum; mx, maxillae; md, mandibles; la, labium; and head sensilla grouped into clusters lab_qua, ver_tri, gen_tri, max_esc [41]. c, d Thoracic segments. e Abdominal segments (ventro-lateral view). f Abdominal TSOs, g ant_TSO, h BSM. i In the 1st larval stage, the CSGs have a bulb-shaped tip. j Open pore at the tip of a CSG at 2nd larval stage. k Schematic representation of 1st stage larvae showing the different types of ESOs, dorso-lateral view. Grey lettering indicates sensilla, which were not analysed in the RNAi experiments. The dashed line indicates the dorsal midline. Sensilla abbreviations, head: ant_TSO, antennal trichoid sensillum (olfactory); lab_qua, labrum quartet; ver_tri, vertex triplet; gen_tri, gena triplet; max_esc, maxilla escort. Thorax: adBSM, anterior-dorsal basiconic sensillum (mechanosensory); alBSM, anterior-lateral basiconic sensillum (mechanosensory); alCSM, anterior-lateral chaetoid sensillum (mechanosensory); dCSG, dorsal chaetoid sensillum (gustatory); dCSM1–2, dorsal chaetoid sensillum (mechanosensory) 1–2; mdBSM1–3, median-dorsal basiconic sensilla (mechanosensory) 1–3; pdBSM1–3, posterior-dorsal basiconic sensilla (mechanosensory) 1–3; plCSM, posterior-lateral chaetoid sensillum (mechanosensory). Abdomen: adBSM1–3, anterior-dorsal basiconic sensillum (mechanosensory) 1–3; alBSM, anterior-lateral basiconic sensillum (mechanosensory); dCSG1–2, dorsal chaetoid sensillum (gustatory); lTSO, lateral trichoid sensillum (olfactory); pdBSM, posterior-dorsal basiconic sensillum (mechanosensory); vTSO1–2, ventral trichoid sensilla (olfactory) 1–2