Voucher specimens representing all sampled species are deposited in the Entomological Museum of Northwest A&F University. Specimen information is presented in Table 1.

The dried wings of male skippers were selected. An appropriate size of wing surface containing the scent glands patches was cut using scissors. The samples were picked up by tweezers and were then stuck on to conductive adhesive. Each sample was given a number and its position was recorded. Samples were attached to a holder using electric adhesive tape, sputter coated with gold and observed and photographed with an S-4800 scanning electron microscope (at accelerated pressure 10.0 kV).

Under the scanning electron microscope, the ultrastructure images of scent glands patches of nine species and their surrounding ordinary scales were obtained. Adobe Photoshop CS6 software was used to measure the length, breadth and aperture of androconia. All measurement data were analysed for variance and multiple comparisons using Excel and SPSS 24.0 software.

Androconia were observed in seven of the nine species selected. The length, breadth, aperture, shape and longitudinal ridge direction of the androconia were observed and measured (Table 2). The androconia have been analysed by variance analysis amongst species and subfamilies.

In terms of length, the results of multiple comparisons of androconia show that there are significant differences amongst the subfamilies, except for Coeliadinae and Pyrginae. Except for the group of T. colon, H. taminata and P. alveus and another group of A. virgata and T. leoninus, there were significant differences amongst species (α = 0.05).

In terms of breadth, the results of comparing androconia show that there are significant differences amongst the subfamilies, except for Hesperiinae and Pyrginae, Coeliadinae and Eudaminae. There are no significant differences in the breadth of the two androconia of L. bifasciata, A. virgata and T. leoninus, L. bifasciata and H. taminata, but there are significant differences amongst species (α = 0.05).

In terms of aperture, the results of androconia comparisons show that there are significant differences amongst the subfamilies, except for Eudaminae and Pyrginae. There are no significant differences in the aperture of androconia of T. colon and A. virgata, H. taminata and T. leoninus, L. bifasciata I and P. alveus, but there are significant differences amongst species (α = 0.05).

There are three main locations for scent organs on butterflies: a) Wings. There are different manifestations in different families of Lepidoptera. For example, the main scent glands patches of Danainae and Heliconiinae are in a small part of the central forewing and on the hindwing. Their location on the hindwing is obvious amongst different genera. In addition, there is a specialised bag-like structure on the ventral surface of the hindwing (Boppre and Vane‐Wright 1989; Vane-Wright et al. 2002; de Oliveira Borges et al. 2020). In Pieridae, the scent glands patches are mainly concentrated in the area where the forewings and hindwings overlap (Beserra Nobre et al. 2021). The scent glands patches of Riodinidae and Lycaenidae are located at the forewing tip (Hall and Harvey 2002; Ômura et al. 2015). b) Abdomen. These are characterised by specific plaques distributed in different areas of the abdomen and in tufts of hair at the end of the abdomen that can be turned out in Danaidae and Riodinidae (Hall and Harvey 2002; Simonsen et al. 2012; de Oliveira Borges et al. 2020). c) Appendages. This mainly refers to the upright hair tufts or hair pencils on the hind tibia, which have been reported in Riodinidae, Pyrgus and Coladenia in Hesperiidae (Hall and Harvey 2002; Hernández-Roldán et al. 2014).

The scent organs of Hesperiidae are mainly concentrated in the first type, especially the black, smooth and raised scars on upperside of the forewing, such as a brand formed after animal skin burns, with even a distortion of the veins where they are located. There are obvious differences in markings on the wing surface of other families (Yuan and Yuan 2015).

Since people first became aware of butterflies, they have attracted the attention of researchers with their colourful appearance. The significance of the unique scales of butterflies lies not only in the appreciation of the external image of the butterfly, but also continues to promote the development of bionic technology, biogeography, paleontology and other fields (Ghiradella 1991; Zhong and Shen 2003; Han et al. 2008; Simonsen et al. 2012; Zhang et al. 2015; Yang and Chen 2021). Butterfly scales are divided into basal scales and cover scales. The basal scales are located on the surface of the wing’s membrane and the cover scales cover the basal scales. Most of the basal scales have two to five cracks at the ends, while the brightly coloured surface scales without cracks are smooth, straight or curved (Fang et al. 2007; Han et al. 2008; Qiu and Han 2009; Simonsen et al. 2012; Parnell et al. 2018). The surrounding scales of the nine species of Hesperiidae are composed of more than two kinds of scales, except for T. colon, which has only one basal scale. B. striata, H. taminata, L. bifasciata, P. alveus, A. virgata and T. leoninus have one basal scale and one cover scale; E. montanus has one basal scale and two cover scales; and B. leechi has two basal scales and two cover scales. The scales of scent glands patches showed one type of androconia and one type of cover scale of H. taminata; two kinds of androconia with different shapes and different distributions of L. bifasciata; one kind of paddle-shaped androconia and one kind of cover scale of P. alveus and T. colon; T. leoninus with one kind of androconia and one kind of paddle-shaped cover scale; and A. virgata with one kind of paddle-shaped androconia. No androconia have been found in B. striata, E. montanus and B. leechi. B. striata has two kinds of ordinary scales: one type of basal scale and one kind of cover scale. E. montanus has three kinds of ordinary scales: one kind of basal scale (tender leaf with tooth cracks) and two kinds of cover scales (hairy and bud-like). B. leechi has one kind of cover scale (tile-like).

The scales of Nymphalidae have similar shapes, structures and arrangements, especially the shape and size of the ultrastructure of the wing scales of the same genus which are small, indicating that the genetic relationship between them is close (Fang et al. 2007; Darragh et al. 2017; Stamm et al. 2019). Amongst the four subfamilies observed, P. alveus and E. montanus of Pyrginae; A. virgata, B. leechi, T. leoninus and T. colon of Hesperiinae; and Eudaminae and Pyrginae have one to two species with extremely similar scale types around the scent glands patches. However, this feature has not been found in B. striata and H. taminata of Coeliadinae.

In butterfly behavioural experiments, some studies have shown that the pheromone released from the scent organs plays a decisive role in the identification of related species (Andersson et al. 2007; Friberg et al. 2008; Ômura et al. 2013; Darragh et al. 2019). Previous studies have shown that the androconia are special glandular scales which are the main structural components of the male courtship pheromone system in Lepidoptera (Pivnick et al. 1992; Hall and Harvey 2002; Beserra Nobre et al. 2021).

The morphology of androconia is significantly distinctive amongst different families in Lepidoptera. For example, androconia are oval and flaky in Pieridae, fan-shaped in Lycaenidae, coronal-shaped in Nymphalidae and rod-shaped or paddle-shaped in Hesperiidae. It can be seen that the morphology of androconia can be used as an obvious morphological characteristic for family classification (Kuwahara 1979; Pivnick et al. 1992; Vane-Wright et al. 2002; Ômura et al. 2015; Darragh et al. 2017; Beserra Nobre et al. 2021). A study showed that the morphology of androconia in the same genus can be different, although 13 species of Celastrina (except C. ladon) have fan-shaped androconia. In this study, some species had differences in the size, lamellar microstructure and number of longitudinal ridges of androconia. In addition, the three subspecies of C. argiolus showed significant changes in androconia morphology (Ômura et al. 2015). In the study of the ultrastructure of androconia in Coliadinae, it was seen that the distribution density of androconia is significantly larger than that of the surrounding ordinary scales. This phenomenon is very obvious in Hesperiidae, which seems to alleviate the problem of insufficient wing surfaces. It is speculated that this morphological feature is closely related to the release of a pheromone (Pivnick et al. 1992; Beserra Nobre et al. 2021).

Analysing the observed morphological characteristics of the seven species of androconia in Hesperiidae, it is found that the aperture of androconia is the largest in Hesperiinae. Amongst them, the mean value for T. colon is 0.323 μm, A. virgata is 0.318 μm and T. leoninus is 0.204 μm, followed by H. taminata at 0.200 μm in Coeliadinae and P. alveus at 0.172 μm in Pyrginae. The mean values of apertures are 0.166 μm and 0.140 μm in L. bifasciata. Through multiple comparative analyses, the apertures were found to be extremely different amongst species and subfamilies and the lengths and breadths of androconia were extremely different amongst subfamilies. The classification analysis of apertures is more consistent with existing domestic research in Hesperiidae: (Coeliadinae + (Pyrginae + (Eudaminae + (Heteropterinae + Hesperiinae)))) (Warren et al. 2008, 2009; Yuan 2010). The left helixes of the longitudinal ridge seem to be a unique feature. Is it unique to T. leoninus, to the genus Thymelicus or is it a feature possessed by a higher category? It can, thus, be seen that it is very important to extract the morphological characteristics of androconia insofar as it is of fundamental significance in reflecting our understanding of the phylogenetic relationships between species.