Fig. 2

Sensilla types and distribution on Tribolium castaneum antennae II. a–e SEM images of SBas with one to five prongs. f, f' SEM image of the tenth segment of the antenna with a close-up of the lateral corner (f') containing SCoe, SBas, and mSTri. g, g' SEM image of the ninth segment with a close-up of the lateral corner (g') showing SCoe and mSTri. Chemoreceptive SCoe were previously described as “minute spicule-like sensilla trichoidea” [90], are relatively rare (Additional file 3: Figure S3e), and located besides the lateral corners of segments 9 and 10 (f',g') mostly at the apical side of segment 11 (Fig. 1b''). Chemoreceptive SBas are arranged in an axial ring at the distal margins of all three club segments (f, g, Fig. 1b–b''). For mechanoreceptive mSTri, we identified about 37 on the apical side of segment 11 (Fig. 1b'') and four in lateral corners of segments 9 and 10 (f, f', g, g', and Additional file 3: Figure S3c, h). h Voltex projection based on a CLSM image stack of the tenth segment from the EF1-B-DsRed line displaying CSNs (orange) and autofluorescence of the cuticle (green). The dendrites of the CSNs converge into the SBas (on average, six per prong), while the axons unite at the center of the segment and join the antennal nerve (AN). i–i'' Overlay of the signals of the DsRed reporter (magenta, i') and the Orco antibody (green, i'') together with DAPI staining (light blue) in the EF1-B-DsRed line, demonstrating a high level of colocalization between DsRed and Orco in segments 9 and 10, but not in 11, where some DsRed-immunoreactive CSNs are spared (compare with Additional file 1: Figure S1a). AN antennal nerve, CLSM confocal laser-scanning microscopy, CSN chemosensory neuron, mSTri mechanosensilla trichoidea, Orco odorant receptor co-receptor, SBas sensilla basiconica, SCoe sensilla coeloconica, Seg segment, SEM scanning electron microscopy