Ctesias (s. str.) serra (Fabricius, 1792)

Kadej, Marcin, 2018, Larva and pupa of Ctesias (s. str.) serra (Fabricius, 1792) with remarks on biology and economic importance, and larval comparison of co-occurring genera (Coleoptera, Dermestidae), ZooKeys 758, pp. 115-135 : 116

Ctesias (s. str.) serra (Fabricius, 1792) Figs 1-4, 5-6, 7-15, 16-21

Material examined.

(2 larvae) Polonia, Brzóza distr. Kozienice 7.VII.1956, w próchnie pnia lipy [inside the mould of the trunk of linden Tilia spp.], leg. B. Burakowski, det. M. Mroczkowski 1956; (2 larvae) Polonia, Maciejowice distr. Kozienice 6.VII.1956, w próchnie (bielu) dębu koło chodników Anobiidae [inside the mould of the oak Quercus spp. next to corridors of Anobiidae ], leg. B. Burakowski, det. M. Mroczkowski 1956; (1 larva) Polonia, Maciejowice distr. Kozienice 6.VII.1956, pod korą olchy [under the bark of alder Alnus spp.], leg. B. Burakowski, det. M. Mroczkowski 1956; (7 larvae) Puszcza Kampinoska, Sieraków, 31.X.1952, pod kora dębu [under the bark of the oak Quercus spp., leg. M. Mroczkowski]; (1 exuvia, 1 pupa) Warszawa, Saska Kępa pod korą wierzby [under the bark of willow Salix spp.] 10.V.1955, leg. M. Mroczkowski; (1 exuvia, 4 larvae) Polonia, Dojlidy ad. Białystok 19.III.1959 leg. R. Bielawski, det. M. Mroczkowski 1959; (1 larva) Germania: Brandenburg, Berlin, Schorfheide, 1.IV.1994. leg. A. Herrmann, coll. A. Herrmann. All materials (except for the last larva) are deposited in the Department of Invertebrate Biology, Evolution and Conservation, University of Wrocław, Przybyszewskiego 65, PL–51– 148 Wrocław, Poland.

Description.

Larva, last instar. Length 5.0-7.0 mm. Body fusiform, relatively long, rather flattened, not hunchbacked. Integument of head, nota and terga yellowish brown to brown; tergal plates sclerotised (Fig. 1), sterna only partially hyaline (= sterna I–VIII with central median line with strongly sclerotised and shiny strip (Fig. 2)), femora and tibiae light yellowish (Figs 1-2). On thoracic terga (= nota I–III) there are darker spots or patches present. Setae (spicisetae and hastisetae) on tegra brown (Fig. 1). On sterna only brown scaly-like spicesetae present (Fig. 2). Head protracted and hypognathous. Six stemmata present on the head (four + two other below). Frons triangular, without frontal, median tubercle (Fig. 8). On the frons two kinds of spicisetae present: lanceolate (= nudiseta) and scale-like. Lanceolate setae situated along anterior margin and on the central area, while scaly spicisetae along lateral margins and in the posterior part of the plate; several also present on the central area among lanceolate setae. Antennae orientated anterolaterally; composed of three antennomeres (Fig. 7). Terminal antennomere 4.0 times as long as wide, with one small sensory sensillum (appendage) on apex and two campaniform sensillae (upper one small, lower one bigger). Ratio of length of terminal antennomere to length of penultimate and antepenultimate antennomeres combined nearly 1.0:5.0. Sensorium in ventral position not extending above apex of segment 2. One campaniform sensillum present on antennomere 2 under sensorium. Antennomere 1 with 6-7 long setae (Fig. 7). Gula separate from postmentum; epicranial stem present. Median endocarina absent. Labro-epipharyngeal margin with 8 to 11 setae in the outer series. Mesal labro-epipharyngeal setae (mp) spatulate (broad) while second pair (p2) stout (narrow). On ventral side of epipharynx basal transverse row (br) of placoid sensillae present (13 to 18 sensory cups in the proximal transverse series (br)). Epipharyngeal rods (er) present and diverging proximally. Four sensory cups in the subproximal epipharyngeal sensilla (sbp), two large and two small ones. Distal epipharyngeal sensillae (dst) arranged in one group of six (in two longitudinal series of three sensillae, Fig. 11). Lateral setae on epipharynx absent (Fig. 11). Dorsal surface of labro-epipharynx with many setae. Mandible brown with dark brown (almost black) apex; apical teeth and ventral accessory process absent. Apical half of mandible heavily sclerotised and sharply delineated from basal half (Figs 9, 10). Mandibular mola and pseudomola absent. Hyaline lobe at ventral base of mandible absent. Prostheca perhaps absent, brush of setae absent mesally near mandibular base. Placoid sensillae (pls) present in approximately one-third of the basal dorso-lateral length of mandible (Fig. 10). Maxillary palp composed of three palpomeres with terminal palpomere longest. Ratio length of terminal palpomere to length of the two proceeding palpomeres combined 1.0:1.5. First palpomere with variable combination of setae and campaniform sensilla:, two setae (one campaniform sensillum) or four setae (one campaniform sensillum). Second palpomere with 2-3 setae and 1-4 campaniform sensillae. Third palpomere with one campaniform sensillum, one short seta subapical and group of small sensillae situated in the apical area. Lacinia with one heavily sclerotised lacinial tooth, straight at apex. Lacinia sclerotisation separated from stipes. Seven straight thick to slender setae present in a dorsomesal row on lacinia (dmr) (Fig. 12). Mesal row of setae on lacinia (msr) composed of a basally thickened seta (Fig. 13). Galea arising from stipes, ending close to the apex of lacinia. The apical area of galea covered densely with setae. Stipes with 18-20 long setae placed mainly near the antero-lateral margin, one to two setae present near the inner margin (under the first palpomere) (Fig. 13). Hypopharynx hyaline. Bridge sclerite (central part of the distal element of the hypopharyngeal sclerome) appearing jointed medially. Anterior arms of bridge sclerite and distal lateral sclerites of hypopharynx absent. Ligula with approximately 21 lanceolate setae (Fig. 14). Labial palp with 2 palpomeres. First segment wider than second segment; 2.0 times as wide as long, with four setae on the disc (sometimes setae absent - they can be lost during dissection - then resembling campaniform sensillae). Terminal labial palpomere with group of small sensillae in the apical area, one campaniform sensillum (cs) close to external margin and three setae on inner margin (Fig. 15).

Antecostal suture on notum I absent, but distinct on nota II–III and abdominal terga I–VII (Figs 18 and 19); abdominal segment VIII without suture or only remnant remaining (Fig. 20). Acrotergites of notum I without setae, while acrotergites of nota II–III and abdominal terga I–VIII with short setae (Figs 18-20). Notum I with long, stout, large spicisetae along anterior (here directed anteriorly under the head), lateral and posterior margin (here directed latero-posteriorly and vertically - upright). Setae on posterior margin situated near the latero-posterior angle, some additionally near suture, some also present on central area of disc of notum I (Fig. 16). Nota II, III with median row of large spicisetae, and along lateral margins of terga. Abdominal terga I–VII with posterior rather than median row of large spicisetae, and along lateral margins of terga (Figs 18-19). These mainly directed latero-posteriorly and vertically (upright). Hastisetae are present both on nota as well as abdominal terga (Figs 16, 18-20). Hastisetae of abdominal terga IV–VII forming dense lateral brushes (longest and thickest on V–VII). Setal patterns of abdominal tergum I with numerous large spicisetae in posterior row; lateral margin bearing also spicisetae; hastisetae on posterior half of tergite more numerous than spicisetae (Fig. 18). Abdominal tergum VII with short, stout setae along anterior margin; large spicisetae in posterior row above the membranous area bearing densely situated hastisetae (Fig. 19). Abdominal tergum VIII without pair of abdominal pits (oval apertures); setal patterns as illustrated (Fig. 20) - short, stout setae along anterior margin; large spicisetae in posterior part. Abdominal tergum IX reduced with numerous long scaly-like spicisetae (Fig. 21). Legs (tibia, femur and trochanter) covered with many lanceolate setae as illustrated on Fig. 17. Claws dark brown. Ratio tibial to femoral length 4.0:5.0. Pretarsus with two narrow lanceolate setae inserted at base. Length of posterior pretarsal seta subequal to length of anterior pretarsal seta (Fig. 17), anterior pretarsal seta perhaps slightly longer.

Pupa (Figs 5-6): length 4.0-5.0 mm. Integument yellowish brown with erect, brown coloured spicisetae distributed rather uniformly on head, dorsum and wings. Head directed downwards (not visible from above). Antennae long, reaching lateral margin of pronotum. Antenna with 11 antennomeres (the boundaries of individual segments not sharply delimited); antennal club with 3 antennomeres (Fig. 6). Antennal club serrated, shorter than flagellum. Eyes clearly visible, convex, oval; situated just behind upper margins of antennae. Pronotum transverse, widest near mesonotum (between posterior angles), with the anterior part narrowed; posterior border of pronotum distinctly elongated in the middle; posterior angles slightly rounded. Mesonotum half as long as metanotum. Mesonotum and metanotum slightly convex. Mesonotum with distinct tubercula in the central part of the disc. Hind wings shorter than fore wings, reaching posterior margin of abdominal segment IV (Fig. 5). The width of abdominal segments I–IV gradually broadened, while V-VIII narrowed posteriorly (Fig. 5). Abdominal segment IX with two black processes (Figs 5-6) (from lateral view these processes slightly curved upward). Abdominal segment IX emarginated in the middle. Legs visible, well developed. Gin traps absent (Fig. 5). Pupa remains within the last exuvium (= larval skin) which is interrupted from head to last abdominal terga ( Donisthorpe 1897, 1920). Probably pupa anchored by two clusters of long fine setae inserted on each side of the abdominal tergum VIII.

Biology.

Knowledge of the biology of the species is limited, with only a small amount of published information ( Donisthorpe 1920, Mroczkowski 1975, Peacock 1993). There is probably only one generation a year. In Poland, adults occur from May to July and sometimes August. Beetles have been recorded from under bark, from tree cavities, by sap flows, and on flowers (where they usually copulate). The eggs are laid under the bark of trees and usually number ca. 20-40. The larvae hatch after 2-3 weeks, passing through usually five instars. Pupation takes place in Autumn or Spring (in April). Since both larvae of the last instar and pupae have been observed under bark throughout the winter, it appears that the species can overwinter as either a pupa or larva. It is known that larvae live under the bark of the mature trees (of different species such as: oak, poplar, elm, sycamore, hawthorn, fir, beech, horse and sweet chestnut, maple, redwood, cherry and willow), close to spiders’ webs, where they feed on dead insects (Rees 1946, Burakowski et al. 1986, Peacock 1993, Kadej 2005). They also feed on clutches of butterflies eggs ( Mroczkowski 1975, Peacock 1993). Occasionally, larvae have been observed in the nests of Aculeata, where they feed on the larval exuviae. They have also been found in insect galleries (e.g. cerambycid Nothorhina punctata (Fabricius, 1798)), in old fungus, and in rotting trees and stumps of mainly deciduous trees ( Hämäläinen and Mannerkoski 1984, Peacock 1993). Due to a secretive life they are usually observed as immature stages. The larvae, when disturbed by predators, can erect and vibrate the abdominal brushes of hastisetae ( Donisthorpe 1897, Joy 1920, Rees 1946). This specific way of defence is facilitated by a well-developed supra-anal organ on the last abdominal segment ( Mroczkowski 1975, Peacock 1993).

Economic importance.

Probably because of its rarity, this species has no serious economic importance. However, it is likely that in its natural habitat it can play a positive role in reducing the number of eggs of butterflies classified as pest of forests ( Mroczkowski 1975). Harding (1986) classified the species as an old forest indicator.

Distribution.

Widely distributed in Europe (from the Mediterranean region to the UK and the southern province of Fennoscandia). It has been also recorded from Algeria, Caucasus and Russia (Stavropol) ( Háva 2015).