Bothynus medon (Germar, 1824) AND

de Jesus, Waner Pereira, Martins, Gabriella Torres & Rodrigues, Sérgio Roberto, 2024, Identification and Description of Antennal Sensilla of Bothynus medon (Germar) and Bothynus striatellus (Fairmaire) (Coleoptera: Scarabaeidae), The Coleopterists Bulletin 78 (2), pp. 273-280 : 276-277

BOTHYNUS MEDON

Females of B. medon had an average length of 23.75 ± 0.95 mm, while males had an average length of 25.37 ± 1.3 mm. There was no significant difference between them in terms of length (t = 2.19; df = 10; P <0.05). However, the average body width for females was 14.5 ± 0.57 mm, while it was 15.8 ± 0.99 mm for males, which is significant (t = 2.53; df = 10; P <0.02).

In the case of the proximal lamellae, there were no significant differences in length (t = 0.83; df = 6; P <0.43) or width (t = 2.11; df = 6; P <0.07) between females and males.For the medial lamellae, significant differences were observed in both length (t = 8.25; df = 6; P <0.001) and width (t = 48.60; df = 6; P <0.001) between females and males, with males having longer and wider lamellae. Similarly, for the distal lamellae, significant differences in both length (t = 2.98; df = 6; P <0.02) and width (t = 45.78; df = 6; P <0.001) were noted between females and males, with males again having longer and wider lamellae ( Table 1).

Higher numbers of placoid and coeloconic sensilla were found on the lamellae of male B. medon , with significant differences compared to females for both placoid (t = 59.04; df = 10; P <0.001) and coeloconic sensilla (t = 14.34; df = 10; P <0.001). For basiconic sensilla, no significant differences were observed between females and males (t = 0.46; df = 10; P <0.6). The total number of sensilla was greater in males, with significant differences between females and males (t = 48.28; df = 10; P <0.001) ( Table 2).

Trichoid sensilla, long and thin throughout their extent, resemble fine hairs. These sensilla are found in greater numbers on the external distal and external proximal lamellae of both males and females, as well as on the edges of the medial lamella ( Fig. 3A ). Chaetic sensilla, which are short, wide, and pointed at their extremity, resemble stout or spine-like setae, can be observed in greater numbers on the external proximal lamella of both males and females ( Fig. 3B ). On the proximal lamella of females (n = 4), 59 trichoid sensilla and 77 chaetic sensilla were quantified, while in males (n = 4), 25 trichoid sensilla and 64 chaetic sensilla were quantified.

Placoid sensilla were identified as types I, II, and III ( Figs. 3C, D , 4D ). Type I placoid sensilla, classified as G2 according to Meinecke (1975), have an irregular shape, a surface with undulations and holes, and an average diameter of 7.47 μm (5.33‒11.11 μm, n = 20). Type II placoid sensilla, classified as G1 according to Meinecke (1975), have a circular or oval shape, a smooth surface, and an average diameter of 7.77 μm (2.66‒13.77 μm, n = 20). Finally, type III placoid sensilla, J4 according to Meinecke (1975), have a circular or oval shape, a flat and smooth surface, occupy the entire cavity where they are inserted, and have an average diameter of 12.04 μm (7.77‒16.66 μm, n = 20).

Coeloconic sensilla were identified as types I and II ( Figs. 3C, D ). They are distributed on the inner surface of the proximal, median, and distal lamellae in both sexes. Type I coeloconic sensilla (L1 according to Meinecke 1975) are short with a sharp tip, while type II sensilla (J1 according to Meinecke 1975) have a flat tip.

Basiconic sensilla were classified as type I (L4 by Meinecke 1975). They are wide and thick and arranged in foveae ( Fig. 4A ). Ampullaceous sensilla (pores) are also present, though in small numbers ( Fig. 4B ).

In female lamellae, a total of 17,477 sensilla were quantified, of which 17,380 (99.44%) are placoid, 76 (0.44%) are coeloconic, and 21 (0.12%) are basiconic ( Table 2). In male lamellae, 21,663 sensilla were quantified, of which 21,525 (99.37%) are placoid, 117 (0.54%) are coeloconic, and 21 (0.09%) are basiconic ( Table 2).

Placoid sensilla of types I and II occurred in various areas of the lamellae. However, type III placoid sensilla, although found in various areas of the lamellae, form a homogeneous area along the lateral inner margin of the median lamella ( Fig. 4C ). In several locations on the lamella surface, foveae are observed, in which placoid sensilla are present ( Fig. 4D ) .

Figures

Fig. 3. Antennal lamella of Bothynus. A) B. medon, distal lamella, outer surface, T = trichoid sensilla, B) B. striatellus, proximal lamella, outer surface, C = chaetic sensilla, C) B. striatellus, medial lamella, inner surface, P I = placoid sensilla type I, P II = placoid sensilla type II, P III = placoid sensilla type III, Co I = coeloconic sensilla type I, D) B. medon, proximal lamella, inner surface, Co II = coeloconic sensilla type II. Scale bar = 200 µm (A), 100 µm (B), 2 µm (C, D).

Fig. 4. Antennal lamella of Bothynus. A) B. striatellus, proximal lamella, inner surface, B = basiconic sensilla, B) B. medon, distal lamella, outer surface, Po = pore, C) B. striatellus, medial lamella, inner surface, A = homogeneous area, B = heterogeneous area, D) B. medon, distal lamella, inner surface, sensilla grouped into a fovea. Scale bar = 20 µm (A, B), 200 µm (C), 10 µm (D).