Agabus browni Kamiya, 1934

Watanabe, Kohei, Kamite, Yuuki, Takechi, Leo & Hayashi, Masakazu, 2025, Description of the instar III larva of Agabus (Acatodes) browni Kamiya, 1934 (Coleoptera: Dytiscidae, Agabinae), Zootaxa 5618 (2), pp. 275-283 : 276-279

The instar III larva of Agabus browni Kamiya, 1934

( Figs 1 , 5–28 )

Source of material: The specimens studied were collected in association with adults at the following localities: One instar III (IIM), Imain, Munakata-shi, Fukuoka Prefecture, Japan, 28 III 2005, Y. Kamite leg.; two instar III (IIM), Osashimachokusumi, Ena-shi, Gifu Prefecture, Japan, 4 III 2023, Y. Kamite & N. Kamite leg.; two instar III (IIM, HOWP), Namikata, Namikata-cho, Imabari-shi , Ehime Prefecture, Japan, 28 III 2023, L. Takechi & A. Shirakata leg.; two instar III (IIM, HOWP), idem, 11 IV 2023, L. Takechi leg. At these sites were found either A. browni alone or accompanied by A. japonicus Sharp, 1873 , which can be distinguished by their head length and width differences.

Diagnosis: The larvae of A. browni can be distinguished from the other two by the following combination of characters: body large, head length approximately 2.0 mm; head width approximately 1.7 mm ( A. japonicus : small, head length approximately 1.6 mm, head width approximately 1.3 mm); abdominal segment VIII with short setae and long hair-like setae ( A. japonicus has only short setae ( Fukuda et al. 1959; Hayashi 2015)); yellow-brown frontoclypeus with one diamond-shaped dark brown macula centrally ( Fig. 1 , 5 ) ( A. conspicuus has many dark brown maculae, and a centrally anterior cross-shaped macula ( Fig. 2 ; Hayashi 2015; Mitamura et al. 2017)).

Color ( Fig. 1 ): Head capsule yellow-brown, with diamond-shaped dark brown macula centrally on frontoclypeus; w-shaped dark brown macula centrally on parietal region; coronal line dark brown; dark brown line laterally from stemmata to temporal spines; neck with T-shaped dark brown macula on each lateral side; stemmata dark brown; antennae light yellow-brown; mandible dark orange; maxilla light yellow-brown; labium light yellow-brown. Body yellow-brown; anterior and posterior regions of pronotum and posterior region of mesonotum, metanotum, and abdominal segments I–VII dark brown; legs yellow-brown; urogomphus yellow-brown.

Body ( Fig. 1 ): Subcylindrical, narrowing towards abdominal apex. Total length 13–18 mm, but this length is highly variable between individuals after molting and mature ones. Other measurements and body shape ratios are presented in Table 1 .

Head ( Figs 5–12 , 16–28 ): Cephalic capsule ( Figs 5 , 16 ) flattened, sub-rounded, longer than broad, maximum width at level of posterior stemmata, constricted at level of occipital region, occipital suture absent, coronal suture elongate, occipital foramen broadly emarginate ventrally; frontoclypeus subtriangular, rounded outwards, anterior margin with approximately 60 variably sized spatulate lamellae clypeales ( Figs 18–19 ). Antenna ( Figs 8 , 20 ) slender, shorter than HL and HW; A4 shortest; A1, A2, and A3 subequal in length; A3’ pore-like. Mandible ( Figs 6–7 , 21–28 ) prominent, broad basally, 2.4–2.7 times longer than wide, apex acute, with groove on inner margin ( Fig. 27 ), distal half serrated on inner ventral margin ( Figs 27–28 ); proximal half of inner ventral margin bearing many brush-like hairs ( Figs 25–28 ), with many spinulae behind these hairs ( Figs 21–22 ). Maxilla ( Figs 9–10 ) with cardo subovate; stipes short, broad, dorsally with many hairs from base to palpifer and many minute spinulae around setae MX 5– MX 6; galea well developed, subconical, dorsally with many hairs and several long setae at base; palpifer short, palpomere-like, with dorsodistal spinulae and short hairs; palpus three-segmented, MP2 longest, MP1 and MP3 subequal in length. Labium ( Figs 11, 12 ) with prementum sub-rectangular, broader than long, with minute spinulae on dorsobasal surface; palpus two-segmented, LP1 longer than LP2.

Thorax ( Figs 1 , 13, 14 ): TI and TA with strong spinulae along ventral margin.

Abdomen ( Figs 1 , 15 ): All sclerites with anterotransverse carina, covered with minute spinulae; segments I–VII transverse; segment VIII subcylindrical, extending dorsally into a short siphon; segments I–V sclerotized dorsally, membranous ventrally; segment VI completely sclerotized except for a ventral narrow area; segments VII–VIII completely sclerotized; spiracles present on segments I–VII; tergites I–VI and anterior region of tergite VII with sagittal line, tergite VIII without sagittal line. Urogomphus two-segmented, longer than LAS, with segment 2 very short.

Chaetotaxy: Similar to that of the generalized Agabus larvae ( Alarie & Michat 2020). Cephalic capsule with minute spinulae on dorsobasal surface ( Figs 16–18 ). Parietale with 3–6 temporal spines on lateral surface ( Fig. 5 ). Antenna without secondary setae. Mandible with several secondary setae, one long seta behind pore MNa ( Figs 7 , 26 ), other setae minute, inserted near outer margin from behind pore MNc to near apex ( Figs 6 , 21–24, 26 ). Setae MX 5– MX 6 stout, strongly curved posteriorly ( Fig. 10 ); stipes with two secondary minute setae ventrally, one posteromesal to pore MXb, and another behind seta MX 2 ( Fig. 9 ). Legs without natatory setae. Posterior margins of abdominal tergites I–VIII with two pairs of long setae dorsally ( Figs 1 , 15 ), tergites VI, VII, and VIII with two, three, and one ventral pairs, respectively. Numbers and positions of secondary setae on legs are listed in Table 2 .

Ecology: Agabus browni are generally found and reproduces in ponds ( Figs 3−4 ). Instar III larvae were collected in March and April, which suggests that A. browni overwinter at larval stage or reproduce in winter in Japan.

Figures

FIGURES 1–4. Agabus spp. larvae and reproductive habitats. 1, Instar III larva of Agabus browni Kamiya, 1934; 2, instar III larva of A. conspicuus Sharp, 1873; 3, reproductive habitat in Gifu Prefecture; 4, reproductive habitat in Ehime Prefecture.

FIGURES 5–12. Instar III larva of Agabus browni. 5, Cephalic capsule, dorsal aspect; 6, mandible, dorsal aspect; 7, same, ventral aspect; 8, antenna, ventral (left) and lateral (right) aspect; 9, maxilla, ventral aspect; 10, same, dorsal aspect; 11, labium, dorsal aspect; 12, same, ventral aspect. *, Additional sensilla.

FIGURES 13–15. Instar III larva of Agabus browni. 13, metathoracic leg, anterior aspect; 14, same, posterior aspect; 15, abdominal segment VIII and urogomphus, dorsal aspect.

FIGURES 16–20. Scanning electron micrographs of Agabus browni, instar III: 16, cephalic capsule, dorsal aspect; 17, right adnasalia, dorsal aspect; 18–19, anterior margin of frontoclypeus, dorsal aspect; 20, antennomeres III–IV, ventral aspect.

FIGURES 21–28. Scanning electron micrographs of Agabus browni, instar III: mandibles. 21–26, right mandible. 21, 23, 24, dorsal aspect; 22, outer aspect; 25, 26, ventral aspect; 27, 28, left mandible, inner aspect.