Coptotomus interrogatus (Fabricius)

Barman, E. H., 2004, A Description of the First Instar Larva of Coptotomus interrogatus (Fabricius) (Coleoptera: Dytiscidae: Coptotominae) with an Emphasis on Cranial Morphology and Comments on the Phylogeny of Basal Lineages of Dytiscidae, The Coleopterists Bulletin 58 (4), pp. 661-671 : 661-671

Description of First-instar of Coptotomus interrogatus (Fabricius)

Color (alcohol preserved, newly hatched specimens). Translucent with light yellowish-tan areas on the head capsule, antennae, and mandibles. Head ( Figs. 1–2 ). Length 0.75–0.84 mm (‾ x ¼ 0.79 6 0.03 mm); almost trapezoidal in dorsal view, widest near origins of antennae, width 0.49–0.56 mm (‾ x ¼ 0.53 6 0.02 mm); with a declination of about 378 (hypoprognathous) anterior to poorly defined cervical region ( Fig.2 ); cervical region deeply emarginate posteroventrally; lacking occipital suture; coronal suture 0.45–0.51 mm (n ¼ 3); frontoclypeus broadly triangular in dorsal view with anterodorsal (cranial) horns, anterior margin beneath horns broadly rounded between modified adnasale and with a distinct sub-rectangular labrum (ventral view, Fig. 1 ); egg-bursters (frontal tubercles) originating on frontoclypeus, anterior to anterior stemmata; six stemmata arranged in a circle; temporal spines absent, each cranial horn bearing a ventrodistal lamellate sensillum (clypealis lamellum), parietal area with primary sensilla of Matus present; frontoclypeus with nine pairs of sensilla. Antenna. Length, 1.02–1.20 mm (‾ x ¼ 1.09 6 0.05 mm); antennomere one, 0.35– 0.41 mm (‾ x ¼ 0.38 6 0.02 mm), antennomere two, 0.18–0.28 mm (‾ x ¼ 0.25 6 0.03 mm), antennomere three, 0.35–0.44 mm (‾ x ¼ 0.39 6 0.03 mm), with a finger-like accessory appendage(A39), antennomere four, 0.06–0.08 mm (‾ x ¼ 0.07 6 0.01 mm), A39 ca. 0.33 the length of antennomere four. Mandible ( Fig. 3 ). Falcate with channel, length greater than width, basal half scaled or spinulate, ventromedial surface toothed distal to well-developed pubescence. Maxilla ( Fig. 4 ). Cardo reduced, stipes prominent, galea finger-like; palpomere one, 0.15–0.25 mm (‾ x ¼ 0.17 6 0.03 mm), palpomere two, 0.13–0.17 mm (‾ x ¼ 0.15 6 0.01 mm), palpomere three 0.23–0.28 mm (‾ x ¼ 0.24 6 0.02 mm); primary sensilla of Matus present. Labium ( Fig. 5 ). Short, about twice as wide as long and convex distally, palpomere one 0.22–0.28 mm (‾ x ¼ 0.24 6 0.02 mm), palpomere two 0.24–0.27 mm (‾ x ¼ 0.26 6 0.01 mm); prementum with a pair of small ventroproximal sensilla (LA 1), and one short (LA 6), one long hair-like (possibly LA 2), and 7–8 large blunt sensilla near the base of each palpus, 4 large blunt medial sensilla; palp with sensilla LA 9 and LA 11 present, LA 10 and LA 12 not observed. Thorax. Pronotum widest posteriorly, about twice as long as mesonotum but narrower; mesonotum slightly narrower than but subequal in length to metanotum; pronotum with long hair-like setae discally; meso- and metanota with hair-like setae on postero-lateral margins and iregularly distributed discally; spiracles absent. Legs ( Figs. 6–7 ). Respective lengths of pro-, meso-, and metalegs, 1.29–1.45 mm (‾ x ¼ 1.39 6 0.05 mm), 1.32–1.61 mm (‾ x ¼ 1.48 6 0.08 mm), 1.64–1.78 mm (‾ x ¼ 1.74 6 0.05 mm); natatory sensilla and tarsal microspinular series ( Nilsson 1988) absent; tibiae and tarsi with numerous spinulae, ventral spinulae present, robust and spine-like on tibiae; anterior claw longer than posterior claw; coxae elongate, coxal sutures absent, primary sensilla of Matus larva present; CO 6 and CO 7 small, CO 6 anterodorsal, CO 7 anterodorsal, proximal, and superior to pore COa; trochanter with primary sensilla of Matus present; femur with 10 to 11 sensilla, 3 to 4 fewer than Matus, FE 1 inserted distally, FE 5 short and spine-like, four anteroventral sensilla (FE 7 –FE 10) with one unnamed anteroventral sensillum between FE 9 and FE 10 on each right leg of one specimen, one unnamed sensillum near FE 4 on one metathoracic leg; tibia with TI 6 short and spine-like; tarsus with TA 2 small and anterodorsal. Abdomen. Segments 1 to 7 lacking spriracles, weakly sclerotized dorsally and bearing long, widely dispersed hair-like setae, menbranous dosolaterally, laterally, and ventrally; segments 1 to 6 each with pair of well developed trachael gills extending laterally, each bearing a medial sensillum; segment 8 completely sclerotized, length 0.30– 0.45 mm (‾ x ¼ 0.34 6 0.05 mm) with poorly developed siphon, length 0.05–0.09 mm, larger primary sensilla of Matus present, if present smaller sensilla (e.g., AB 14) obscured by numerous spinulae. Urogomphus. One-segmented, length 1.19–1.31 mm (‾ x ¼ 1.24 6 0.04 mm); eight sensilla of Matus larva present with numerous spinulae and additional sensilla.

Biology

Gravid beetles were collected from small ephemeral pools that were dry within 14 days of collection of the adult material. In culture, creamy-white and minutely reticulate eggs (length, 0.81–0.90 mm, ‾ x ¼ 0.86 6 0.04 mm; width, 0.27–0.30 mm, ‾ x ¼ 0.29 6 0.01 mm; n ¼ 10) were attached individually onto the surfaces of leaves of Brazilean elodea. Incubation was 10–11 days. Some egg mortality occurred because of damage caused by herbivory on the surface of leaves by small physid snails, unintentionally introduced into the oviposition vessels on elodea fragments.

Figures

Figs. 1–2. Cranium of Coptotomus interrogatus (Fabricius). 1) Dorsal and ventral surfaces of cranium; 2) lateral view. Legend: AN, origin of antenna; DA, declination angle; EB, egg bursters; CH, cranial horn; FR, frontoclypeus; LM, labrum; LS, lamellate sensillum; MN, mandible; NS, nasale; PA, parietale; and TP, posterior tentorial pit. Numbers refer to primary sensilla corresponding to those named on larval Matinae (Alarie et al. 2001).

Figs. 3–5. Ventral views of mouth parts of Coptotomus interrogatus (Fabricius). 3) Maxilla; 4) mandible; 5) lateral half of labium. Legend: CD, cardo; GA, galea; LP, labial palp; MP, maxillary palp; PM, prementum; ST, stipes. Numbers refer to primary sensilla corresponding to those named on larval Matinae (Alarie et al. 2001).

Figs. 6–7. Prothoracic leg of Coptotomus interrogatus (Fabricius). 1) Anterior view; 2) posterior view. Legend: CO, coxa; FE, femur; PTS, pretarsal sensilla; TA, tarsus; TI, tibia; TR, trochanter. Numbers refer to primary sensilla corresponding to those named on larval Matinae (Alarie et al. 2001).