Comparative Ultrastructure and Ecological Adaptation of Adhesive Setae in Four Species of Longhorn Beetles (Coleoptera)

Abstract

Longhorn beetles mainly harm trees, flowers, and certain crops. They are closely associated with their host plants and often climb on vertical trunks, branches, and the underside of leaves. Their tarsi have numerous micro-scale adhesive setae on the ventral side. These setae provide sufficient force to enable the beetles to adhere firmly to smooth or slightly micro-structured surfaces. This study observed and analyzed the ultrastructures of the adhesive setae of three species from different subfamilies of Cerambycidae and one species from Vesperidae using a scanning electron microscope. The comparative analysis focused on characterizing the types, morphology, distribution patterns and adhesion mechanisms of the adhesive ultrastructures in four longhorn beetle species. The results showed that the longhorn beetles generally had pseudotetramerous tarsi (except An. chinensis, which had tetramerous tarsi), and that tarsomeres I-III were expanded and widened to increase the contact area between the tarsi and the substrate. Furthermore, a large number of micro-scale adhesive setae were present on the ventral surface of these tarsomeres. In total, five types of adhesive setae were found in the four species studied. The three species belonging to the Cerambycidae family exhibited adhesive setae with numerous short setules, while in the species Mantitheus pekinensis belonging to Vesperidae, there are two types of adhesive setae without any short setules. The differentiation of the adhesive structures in longhorn beetles is shaped by the combined effects of phylogeny, sexual dimorphism, and host-plant adaptations.

Keywords: Cerambycidae; Coleoptera; Vesperidae; adhesion; scanning electron microscope; ultrastructure.

Figure 2

The tarsi and adhesive setae of Aegosoma sinicum (A–H) and Mantitheus pekinensis (I–P). (A–D) female Ae. sinicum. (A) protarsus, ventral side; (B) unguis (claws); (C) tapered setae; (D) elliptical setae. (E–H) male Ae. sinicum. (E) protarsus, ventral side; (F) unguis (claws); (G) discoidal setae; (H) elliptical setae. (I–L) female M. pekinensis. (I) protarsus, ventral side; (J) unguis (claws); (K,L) tapered setae. (M–P) male M. pekinensis. (M) protarsus, ventral side; (N) unguis (claws); (O) tapered setae, ventral side; (P) discoidal seta, ventral side. Abbreviations: UN, unguis (claw); Tar I, the 1st tarsomere; Tar II, the 2nd tarsomere; Tar III, the 3rd tarsomere; Tar V, the 5th tarsomere; sh, setal shaft; tp, terminal plate; su, setule; arrows, non-adhesive setae.

Figure A1

Replicates of the tarsi and adhesive setae of Aromia bungii (A–H) and Anoplophora chinensis (I–P). (A–D) protarsi of Ar. bungii, ventral side. (A,B) female protarsi; (C,D) male protarsi; (E,F) long spindle-shaped setae in females, ventral side; (G,H) long spindle-shaped setae in males, ventral side. (I–L) protarsi of An. chinensis, ventral side. (I,J) female protarsi; (K,L) male protarsi; (M) spindle-shaped adhesive setae in females, dorsal side; (N) Spindle-shaped adhesive setae in females, ventral side; (O,P) discoidal seta in males, ventral side. Abbreviations: UN, unguis (claw); Tar I, the 1st tarsomere; Tar II, the 2nd tarsomere; Tar III, the 3rd tarsomere; Tar V, the 5th tarsomere.

Figure A2

Replicates of the tarsi and adhesive setae of Aegosoma sinicum (A–H) and Mantitheus pekinensis (I–P). (A–D) protarsi of Ae. sinicum, ventral side. (A,B) female protarsi; (C,D) male protarsi; (E) tapered setae in females; (F) elliptical setae in females, ventral side; (G) discoidal setae in males, ventral side; (H) elliptical setae on the margin of the tarsi in males, ventral side. (I–L) protarsi of M. pekinensis, ventral side. (I,J) female protarsi; (K,L) male protarsi; (M) unguis (claws) in female; (N) tapered setae in females; (O) tapered setae in males; (P) discoidal setae in males, ventral side. Abbreviations: UN, unguis (claw); Tar I, the 1st tarsomere; Tar II, the 2nd tarsomere; Tar III, the 3rd tarsomere; Tar V, the 5th tarsomere.

Figure 1

The tarsi and adhesive setae of Aromia bungii (A–H) and Anoplophora chinensis (I–P). (A–D) female Ar. bungii. (A) protarsus, ventral side; (B) unguis (claws); (C) long spindle-shaped setae; (D) spatulate setae; (E–H) male Ar. bungii. (E) protarsus, ventral side; (F) unguis (claws); (G) long spindle-shaped setae, ventral side; (H) long spindle-shaped setae, dorsal side. (I–L) female An. chinensis. (I) protarsus, ventral side; (J) spindle-shaped adhesive setae, dorsal side; (K) spindle-shaped adhesive setae, ventral side; (L) spatulate setae. (M–P) male An. chinensis. (M) protarsus, ventral side; (N) discoidal seta, dorsal side; (O) discoidal seta, ventral side; (P) spatulate setae. Abbreviations: UN, unguis (claw); Tar I, the 1st tarsomere; Tar II, the 2nd tarsomere; Tar III, the 3rd tarsomere; Tar V, the 5th tarsomere; sh, setal shaft; tp, terminal plate; su, setule; arrows, non-adhesive setae.

Figure 3

Male behavior during mating. (A) Ar. bungii on the peach tree (Huanggang, Hubei, China, photographed by Chuangyu Lao). (B) An. chinensis (Naji Islands, Zhejiang, China, photographed by Suyan Cao). (C) Ae. sinicum on the willow tree (China National Botanical Garden, Beijing, China, photographed by Dakang Zhou). (D,E) M. pekinensis. (China National Botanical Garden, Beijing, China, photographed by Dakang Zhou).

Figure 4

Ultrastructure of the female elytra in four longhorn beetle species. (A–D) The female elytra of Ar. bungii. (A) The lateral margins. (B) The central area. White arrows, micro-scale irregular structures (C,D) Setae on the lateral margins. (E–H) The female elytra of An. chinensis. (E) The lateral margins. White arrows, the setae of type I. Black arrows, the setae of type II. (F) The central area. Black arrows, the setae of type III. (G) Setae on the lateral margins. White arrows, the setae of type I. Black arrows, the setae of type II. (H) Setal clusters of the white spots. Black arrows, the setae of type III. (I–L) The female elytra of Ae. sinicum. White arrows, the raised ridges. Black arrows, the elliptical sockets. (I) The upper-median section of the elytra. (J). The longitudinal carina of the elytra. (K,L). The elliptical seta sockets on the lateral margins. (M–P). The female elytra of M. pekinensis. White arrows, the setae. Black arrows, the pores. (M) The median section of the elytra. (N) The lateral margins. (O,P) Setae on the lateral margins.