A Comparative Morphological Study of the Ultrastructure of Antennal Sensilla in Sclerodermus guani (Hymenoptera: Bethylidae)

Abstract

The morphology, number, and distribution of antennal sensilla differ between males and females, reflecting adaptations to sex-specific ecological roles and life histories. In this study, scanning electron microscopy was employed to examine the antennal structure and sensilla types of adult males and females of Sclerodermus guani Xiao et Wu 1983 (Hymenoptera: Bethylidae), with a focus on identifying morphological differences between the sexes. The results revealed that the antennae of both sexes are geniculate; however, female antennae are shorter and broader than those of males. Each antenna comprises 13 segments, including a scape (1 segment), a pedicel (1 segment), and a flagellum (11 segments). Eight distinct types of sensilla were identified on the antennae of both males and females, with notable sex-specific differences in sensilla types and subtypes. Trichoid sensilla subtype III was found exclusively in males, whereas long basiconic sensilla and basiconic sensilla subtype II were unique to females. More than 70% of the antennal sensilla in both sexes were olfactory in nature, highlighting their predominant role in chemical detection. The observed sexual dimorphism in the morphology and distribution of olfactory sensilla suggests functional specialization, potentially linked to host localization in females and mate location in males.

Keywords: Sclerodermus guani; antennae; morphology; olfactory sensilla; scanning electron microscope.

Figure 1

Antennal morphology of female and male Sclerodermus guani. S. guani female dorsal view (a1) and ventral view (a2); S. guani male dorsal view (b1) and ventral view (b2). Rd, radicula; Sc, scape; Pe, pedicel; Fu, funicle; Cl, clava; Fl, flagellum; F₁ to F₁₁, flagellomere segment 1 to flagellomere segment 11; Jo, wide membranous joint between the scape and the pedicel; scale bar = 100 μm. Abbreviations follow Table 1.

Figure 2

Comparison of the antennal segment length and width between female and male Sclerodermus guani. (a) The length of each antennal segment; (b) the width of each antennal segment. The comparison was conducted using an independent samples t-test; NS, p > 0.05; *, p < 0.05; ***, p < 0.001. Columns and bars represented mean ± standard error (n = 10). Abbreviations follow Table 1.

Figure 3

The percentage of each sensilla type in the male (a) and female (b) Sclerodermus guani. Number of sensilla: male, 952.17 ± 4.78 (mean ± standard errors); female, 1276 ± 9.91 (mean ± standard errors). Abbreviations follow Table 1.

Figure 4

Antennal segment morphology of female Sclerodermus guani. Antennal segments include the radicula, scape, pedicel, and flagellum (comprising the funicle and clava), along with the distribution of various types of attached sensilla. (a) dorsal morphology of radicula and scape; (b) view morphology of radicula and scape; (c) pedicel morphology; (d,e) funicle morphology; (f) clava morphology; (g) BB morphology; (h) CS morphology; (i) SS, TS-I morphology; (j) MPS morphology; (k) SCS-I morphology; (l) SCS-II, CS morphology; (m) LBS, BS-I and BS-II morphology; (n) TS-II morphology. The white line in the lower right corner indicates the scale. Abbreviations follow Table 1.

Figure 5

Antennal segment morphology of male Sclerodermus guani. Antennal segments include the radicula, scape, pedicel and flagellum (funicle and clava), as well as the distribution of various types of sensilla attached to them. (a) dorsal morphology of radicula and scape; (b) view morphology of radicula and scape; (c) pedicel morphology; (d,e) funicle morphology; (f) clava morphology; (g) BB morphology; (h) CS morphology; (i) SS morphology; (j) MPS morphology; (k) SCS-I morphology; (l) SCS-II morphology; (m) TS-II, TS-III, BS-I morphology; (n) TS-I morphology. The white line in the lower right corner indicates the scale. Abbreviations follow Table 1.

Figure 6

Antennal sensilla surface detail of Sclerodermus guani. The multiporous plate sensilla of female (a1) and male (b1) Sclerodermus guani; the surface micropore of multiporous plate sensilla in female (a2) and male (b2) Sclerodermus guani. (c1) Styloconic sensilla type I distal portion; (c2) Styloconic sensilla type I base; (c3) Styloconic sensilla type II distal portion; (d) Long basiconica sensilla end portion; (e) Trichodea sensilla type I; (f) Trichodea sensilla type II; (g) Basiconica sensilla type I; (h) Coeloconica sensilla. P: pore; G: groove. The white line in the lower right corner indicates the scale.