Megatoma Herbst, 1792

Kadej, Marcin, 2017, Larva and pupa of Megatoma (s. str.) undata (Linnaeus, 1758) with remarks on biology and economic importance (Coleoptera, Dermestidae), ZooKeys 698, pp. 59-74 : 63-66

Genus Megatoma Herbst, 1792 Figs 1-3, 4-6, 7-16, 17-21

Megatoma (s. str.) undata (Linnaeus, 1758)

Material examined.

One larva, and 15 exuviae. Original label: "Kazimierz n/W 16.10.1950 leg. M. Mroczkowski [Kazimierz under Vistula]"; seven larvae "Polonia Kazimierz n/W, 28.3.1951, cult. M. Mroczkowski [Kazimierz under Vistula] / larwy 16.10.1950 w komorach samotnych pszczół w ścianie lessowej [larvae in the chambers of solitary bees in the wall of loess], leg. M. Mroczkowski". Seven larvae. Original label: "Kazimierz n. Wisłą w gniazdach błonkówek [Kazimierz under Vistula in the nests of Hymenoptera ] 17.V.1955, leg. M. Mroczkowski". Seven exuviae. Original label: "Kazimierz n. Wisłą w gniazdach błonkówek [Kazimierz under Vistula in the nests of Hymenoptera ] 27.V.1955, leg. M. Mroczkowski". One larva, three exuviae, three pupae. Original label: "Kazimierz nad Wisłą [Kazimierz under Vistula] 16.VIII. 1955 ex larva, leg. et cult. M. Mroczkowski".

Description.

Larva, last instar. Body length 5.0-11.0 mm. Body fusiform, relatively long, flattened, not hunchbacked (Figs 1-3). Integument of head, nota, and terga brown. Head darker than terga. Tergal plates sclerotized (Figs 1-2), sterna hyaline and unpigmented (Fig. 3), femora and tibiae light yellowish (Figs 2-3). Thoracic terga I–III with distinctly dark brown patches at sides (Figs 1-3), sometimes extending to middle on terga II and III. Setae (spicisetae and hastisetae) on tegra and sterna brown (Figs 1-3). Head of hastisetae short; 3-4 times long as wide (Fig. 8). Head protracted and hypognathous (Figs 2, 3). Stemmata (probably 5) present on the head, arranged in two semi-oblique rows. Frons triangular (Fig. 9), without frontal, median tubercule; covered with spicisetae and nudisetae (the latter present only at the anterolateral angles of the frons); setal patterns as on Fig. 9. Antennae orientated anterolaterally (Fig. 1); composed of three antennomeres (Fig. 7). Terminal antennomere 3.0 times as long as wide, with two small sensory sensilla (appendages): one on the apex, second one under the apex; and two campaniform sensillae under half of length of antennomere (near base). Ratio of length of terminal antennomere to length of penultimate and antepenultimate antennomeres combined nearly 0.4:1.0. Sensorium in ventral position, below the apex of antennomere II. Single seta present on antennomere II near apex (opposite to sensorium). Three campaniform sensillae present on antennomere II - two under sensorium and one close to the base of the segment. Antennomere I with 3-7 long setae (probably there are not any campaniform sensillae (cs) (Fig. 7)). Gula separate from postmentum; epicranial stem present. Median endocarina absent. Labro-epipharyngeal margin with 12-14 setae in the outer series. Mesal (mp) of labro-epipharyngeal setae and second pair (p2) broad and spatulate. On ventral side of epipharynx distal epipharyngeal sensillae (dst) arranged in one group of 6 in two rows (four in the upper one, and two below), but not encircled by distinct furrow (they are loosely grouped in faintly defined fusiform callosity, Fig. 12). Four to six sensory cups in the subproximal epipharyngeal sensilla (sbp) are present. Middle pair larger and lateral sensilla smaller, directed down to the basal transverse row (br) of placoid sensillae. Epipharynx with nine sensory cups in the proximal transverse series (br). Epipharyngeal rods (er) present and diverging proximally. Lateral setae on epipharynx absent (Fig. 12). Dorsal surface of labro-epipharynx with many setae. Mandible brown with dark brown (almost black) apices; apical teeth and ventral accessory process absent. Apical half of mandible heavily sclerotized and sharply delineated from the basal half (Figs 10, 11). Mandibular mola and pseudomola absent. Hyaline lobe at ventral base of mandible absent. Prostheca falciform (Fig. 10 and 11), brush of setae absent mesally near the mandibular base. Placoid sensillae (pls) present in basal part (in approximately 1/4 of the dorso-lateral length) of mandible (Fig. 10). Maxillary palp composed of three palpomeres with terminal palpomere longest. Ratio of terminal palpomere length to the two proceeding palpomeres combined 1.3:1.0. First palpomere with two seta (on the Fig. 14 one of them is lacking), second palpomere with 3 setae (on the Fig. 14 two of them are lacking), and third palpomere with two campaniform sensillae and group of 5-6 small sensillae situated in the apical area (Fig. 14). Lacinia with two, heavy sclerotized lacinial teeth, straight at apex. Sclerotization of lacinia separated from stipes. Seven to as many as thirteen straight slender to thick setae present in a dorsomesal row on lacinia (dmr) (Fig. 13). Mesal row of setae on lacinia (msr) composed of one basally thickened seta (Fig. 14). Galea arising from stipes terminates close to the apex of lacinia. The apical area of galea covered densely with setae. Stipes with 14-18 long setae placed mainly near the anterio-lateral margin, two setae present near the inner margin (close to the first palpomere) (Fig. 14). 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 13-15 lanceolate setae (Figs 15 and 16). Labial palp with two palpomeres (Fig. 15). First segment wider than second segment; without setae on the disc. Terminal labial palpomere 2.0 times as long as wide, with group of 7-8 small sensillae in the apical area and two campaniform sensilla (cs) (Fig. 14).

Antecostal suture smooth and distinct, present on nota I–III and abdominal terga I–VIII. Acrotergites of notum I without setae (Fig. 17), while acrotergites of nota II–III and abdominal terga I–IX (?) with setae (Figs 18-21). Notum I with long, stout, large spicisetae along anterior (here directed anteriorly under the head) and lateral margin; only few spicisetae located along posterior margin (here directed latero-posteriorly and vertically - upright). The setae on the posterior margin are situated near the latero-posterior angle, with some additionally near the posterior suture, and some also present on central area of disc of notum I (Fig. 17). Nota II, III and all abdominal terga with median row of large spicisetae, and along lateral margins of terga (Figs 18, 20-21). They are mainly directed latero-posteriorly and vertically (upright). Hastisetae present both on nota I–III as well as on abdominal terga I–VIII, forming dense lateral brushes (= tufts) on abdominal terga, but the longest and the thickest are on segments (V) VI–VIII (the aggregation of hastisetae arises even from tergum IV and they become significantly denser and thicker closer to the posterior end of the body). Setal patterns of abdominal tergum I with numerous large spicisetae in median row and along lateral margin; posterior margin (under the median line of spicisetae) bearing mainly hastisetae (Fig. 18). Abdominal tergum VII as illustrated (Fig. 20). Abdominal tergum VIII without pair of abdominal pits (oval apertures); setal patterns as illustrated (Fig. 21). Abdominal tergum IX reduced with numerous long spicisetae (Fig. 19). Legs (tibia, femur and trochanter) covered with many lanceolate setae. Claws dark brown. Ratio of tibial to femoral length 0.8:1.0. Pretarsus with two narrow lanceolate setae inserted at base. Length of posterior pretarsal seta equal to anterior pretarsal seta.

Pupa: length 5.0-7.0 mm (Figs 4-6). Integument yellowish brown with erect, brown coloured spicisetae distributed rather uniformly on head, dorsum, and wings. The longest spicisetae present on head (Figs 4-6). Gin traps and urogomphi absent (Figs 4-5). Pupa remains within the last exuvia (= larval skin, Fig. 4). It is anchored by two clusters of long fine setae inserted on each side of the abdominal tergum VIII.

Distribution.

Widely distributed in Europe. The species has been also recorded from the Caucasus ( Háva 2015).

Biology.

Adults are seen from April to October (in Poland) and can have two generations per year. The species overwinters as either an adult or larva. Individuals can be found on the bark of trees, close to places with leaking sap, under bark (including that of elm, larch, oak, crab apple, sycamore, willow, maple, ash, and beech trees), in spider webs, inside bird nests or boxes, bee hives, or on the walls of old timber-built houses or barns ( Mroczkowski 1975, Peacock 1993, Kadej 2005, Byk et al. 2006).

The immature stages have been found in nests of different Aculeata (where they feed on both their food and exuviae and pupae). Brechtel (1986) and O´Toole (2010) recorded the larva of M. undata from nests of Osmia rufa (Linnaeus, 1758), while Rey (1887) described it from galleries of saproxylic bees Xylocopa violacea (Linnaeus, 1758). It has also been recorded as a predator of the pupae of the moth Lymantria dispar (Linnaeus, 1758) in oak forests ( Mihalache et al. 1995). According to observations of O´Toole (2010) larvae feed on larval exuviae of the red mason bee, their fecal pellets, on the silk cocoons spun by the pre-pupal bees as well as on dead adults. In buildings, larvae feed on products of animal origin such as dry insect specimens in collections, skins, furs, and old wool ( Fowler 1889, Joy 1932, Takano et al. 2012).

Unlike the larvae, adults feed on pollen ( Mroczkowski 1975, Peacock 1993). Beetles were most often found in their breeding sites, and rarely on flowers. Hunter (1959) reported both adults and larva from larval burrows of cerambycids such as Molorchus minor (Linnaeus, 1758), Tetropium gabrieli Weise, 1905 and Anaglyptus mysticus (Linnaeus, 1758). Allen (1958) observed M. undata associated with the spider Salticus scenicus (Clerck, 1757).

Economic importance.

In this regard, this species has low importance because it has never been recorded on a mass scale and occurs mostly in natural conditions ( Mroczkowski 1975). It is generally an “outdoor” species that occasionally enters houses to feed on products of animal origin. Thus, the species has not been classified as a typical pest ( Takano et al. 2012). Moreover, some authors have even classified this species as a saproxylic beetle ( Byk et al. 2006, O´Toole 2010) or a woodland indicator ( Garland 1983).