Belionota prasina (Thunberg, 1789)

Seena, S., Anand, P. P. & Shibu Vardhanan, Y., 2023, Morphology, ultrastructure and sexual dimorphism in antennal sensilla of Belionota prasina (Thunberg, 1789) (Coleoptera, Buprestidae), Journal of Insect Biodiversity and Systematics 9 (4), pp. 663-678 : 665-671

Belionota prasina (Thunberg, 1789)

The general structure of antennae. Antennae comprised of 11 antennomeres: antennomere 1 (scape) and 2 (pedicel) invariable in all specimens and bear only trichiod sensillae; antennomere 3 longer than segment 2; antennomeres 4–10 serrate and highly variable between sexes; antennomere 11 irregular in shape. The location and shape of the sensory organs vary in shape on the apical antennomeres; however, all antennal fossae are open and form long furrows ( Figs 3 & 4)

Types of sensilla. There are five different types of sensilla ( Fig. 2) with their subtypes identified in the antennae of B. prasina : Böhm sensilla, sensilla chaetica (four subtypes), basiconica (five subtypes), sensilla trichodea, and multigrooved peg.

Böhm's sensilla (BS). The sensilla have a tight socket and short, smooth, thorn-like bristles with a sharp tip ( Fig. 5E) which are mainly located at the base of the scape and pedicel. The average length is 23.9±2.6 μm. These are actually sensilla trichodea and recently have been named Böhm sensillae by Böhm who described that in Lepidoptera in 1911.

Sensilla chaetica (C1–C4). Sensilla chaetica can be identified by their longitudinal furrows and specialised, circular rings at their bases, which are inserted in a large circular ring. The bristles of this sensillae are sharp and pointed without apical pores or wall pores. There are four subtypes of sensillae chaetica were identified in both sexes of B.prasina a. Subtype 1 (C1). Aporous sensilla chaetica: Sensilla chaetica 1 are long and slender sensilla, with longitudinal grooves on the wall without pores ( Fig. 5A). In B.prasina these types sensilla are located in the apical region of antennomeres from 4 th to 11 th and which is the longest sensilla with a length of 178.6±1.2 μm.

b. Subtype 2 (C2). Uniporous sensilla chaetica: Sensillae chaetica 2 are curved sensillae ( Fig. 5A), which are shorter than C1 inserted into funnel-shaped depression and the average length is 100.9±2.7 μm.

c. Subtype 3 (C3). Aporous sensilla chaetica: Sensilla chaetica 3 aporous chaetoid sensillae with a basal socket. These are short and stout and the walls are smooth without pores ( Fig. 5B). C 3 type sensillae are located at the sides and outer margins of antennomeres in both sexes. The average length is 33.8±0.03 μm.

d. Subtype 4 (C4). Aporous serrated sensilla chaetica: Aporous serrated sensilla chaetica ( Fig. 5C, D) which are distributed along the inner side of antennomeres in males from 4 th antennomers onwards. The average length of these sensilla is 268.2±31.4 μm

Sensilla basiconica (Sb1-Sb5). All subtypes of sensilla basiconica usually present inside apical organs and their number depends on the size. These are the trichoid type of sensilla without any basal membrane. These come under Type B4.

a. Subtype 1 (Sb1). These are multiporous cone-like sensilla with filamentous tips ( Fig. 6A) present inside the apical organ. The average height of Sb1 is 8.7±0.9 μm.

b. Subtype 2 (Sb2). These sensilla are multiporous peg-like or cone-like sensilla, ( Fig. 6A), and the apical end is curved in appearance. The average length is 5.07±0.5 μm.

c. Subtype 3 (Sb3). Subtype 3 sensilla basiconica is short cone-shaped multiporous sensilla that are flattened and round tip, which is present at the inner margin of the apical organ ( Fig. 6B). The average length of these sensilla is 3.6±0.1 μm,

d. Subtype 4 (Sb4). Short cone-shaped with sharp tip sensilla ( Figs 6C, 6D) having multiporous walls located at upper edges of apical organ only in 4 th flagellomeres in females which comes under type B4 (subtype B4c) and the average length is 6.4±0.8 μm.

e. Subtype 5 (Sb5). Short cone-shaped multiporous basiconic sensilla located singly at the lateral sides of male antennomeres in between the C4 sensilla from 4 th flagellomeres onwards and the average length is 7.6±0.04 μm ( Fig. 6E).

Multiporous sensilla trichodea (MST). Long, slender, and tapering at the tip. It has three glandular pores on one side. MST are present in both sexes with an average length of 22.6±0.1 μm ( Fig. 5F).

Multiporous grooved pegs (MGP). The MGP is a bulbous-headed cone-shaped sensillum having 8 wide grooves running from the middle to the tip ( Fig. 6A). Iit appears singly inside the apical organ only in males. The average length is 2.6±0.2 μm. It comes under type M5 (according to Volkovittsh, 2001) .

Sexual dimorphism. The male antenna is longer (length: 5321.9±144.8 μm) than the female (length: 4351.8±183 μm), as well as the lengths of segments 3 – 11 ( Table 1). Also, male and female antennomeres show considerable variation in their basal and distal widths where, except for segment 11, female antennomeres are considerably wider ( Table 1). The number and types of sensillae is significantly different between the sexes. C4 ( Figs 5C, 5D) is the most noticeable sex difference, is present only in male antennomeres. Sb3 ( Figs 6B) is present in both sexes, but is more numerous in females than in males. Sb4 ( Figs 6C, 6D) is present only in female antennae, while multiporous grooved pegs ( Figs 6A) are present in male antennae. Sb5 ( Figs 6E) is present only in the lateral sides of the 4 th flagellomere onward in male antennae, and the 11th flagellomere is longer and has more C4. This has a somewhat round and small apical organ with less basiconic sensilla. Male and female apical organ arrangements also differed significantly. Male B. prasina antennae have apical fossae on both the dorsal and ventral sides, with the dorsal fossae being small and arranged on the 4 th to the 10 th segments, and the ventral side having well-developed apical fossae with sensilla basiconica on the 4 th to 11 th segments. In females, the apical organ is well developed on the dorsal side of antennomeres 4–11, but it is only present on the ventral side of the 10 th antennomere. In addition, the area and length of apical fossae is different between males and females ( Table 2, Table 3).