Malachius (Malachius) prolongatus Motschulsky, 1866

Asano, Makoto, 2017, Morphology and biology of Malachius prolongatus (Coleoptera: Melyridae: Malachiinae), Acta Entomologica Musei Nationalis Pragae (Acta. Ent. Mus. Natl. Pragae) 57 (2), pp. 603-615 : 605-613

Malachius (Malachius) prolongatus Motschulsky, 1866

( Figs 1–30 )

Malachius prolongatus Motschulsky, 1866: 167 (original description) Malachius (Malachius) prolongatus: EVERS (1985) : 23 (establishment of the subgenus Malachius and key to species)

Additional description of adult ( Figs 1–9 , 27 ). Male. Measurements in mm (n = 2). BL: 6.7 (6.5–6.8); HL: 1.2 (1.1–1.2); HW: 1.4 (1.3–1.4); PL: 1.4 (1.3–1.5); PW: 1.6 (1.5–1.6); EL: 4.1 (4.0–4.1); EW: 2.1 (1.8–2.5); HTL: 2.0.

Head capsule rather wide (HW/HL 1.1); apical margin of frons prominent, with dense short setae and glandularium ( Fig. 6 : gl); gula with a tuft of hairs ( Figs 7, 9 : tf).

Abdomen rather soft; tergite VIII subtrapezoid, long and rather slender ( Fig. 3 ); VIII sternite in caudal margin bifid, each apex hook-shaped ( Fig. 2 ). Endophallus elongate and almost straight. Internal sac ( Fig. 4 : is) with numerous minute spines densely all over the inner surface and with a gonoporal piece ( Fig. 4 : gp) but without ligra. Gonoporal piece with a long and thin sclerite ( Fig. 4 : sc). Spicular fork thin, anterior half cover-up endophallus and posterior part bifid ( Fig. 5 ).

Female. Measurements in mm (n = 2). BL: 6.6 (6.4–6.8); HL: 1.0 (0.9–1.0); HW: 1.4; PL: 1.1 (0.9–1.2); PW: 1.6; EL: 3.9 (3.6–4.2); EW: 1.9 (1.8–2.0); HTL: 1.7.

Head capsule rather wide (HW/HL 1.4), frons simple ( Fig. 8 ), gula with a small tuft of hairs ( Fig. 9 ).

Description of egg ( Fig. 24 ). Length: 1.0– 1.1 mm (n = 2). Light orange in color, chorion unpigmented and transparent. Slender, soft and smooth. Embryos are visible through very thin chorion ( Fig. 24 ).

Description of first instar (larva at the egg hatch) ( Figs 10–13 , 17–23 , 25 ). Measurements in mm (n = 1). BL: 1.07; BW: 0.31; HL: 0.13; HW: 0.20; UL: 0.06.

Body unpigmented and translucent, very soft, rugose, oblong oval in form, setae absent except on antennae and labrum. Yolk stocked in midgut, chorion still covering abdomen ( Figs 10–13 , 17, 18 ). Head capsule subtrapezoidal; setae, pore, frontal arm and epicranial stem indistinct. Labrum distinguishable, with 2 setae. Five stemmata obscurely visible, 3 arranged in transverse row anteriorly and 2 posteriorly ( Fig. 10 , 17 ). Antennae ( Fig. 11 : an) obscurely 3-segmented; segment I short, segment II with a conical sensorium, seta and pore, segment III slender and long ( Fig. 12 ). Mandibles ( Fig. 11 : md) protruding, with two pointed parts, divided from head capsule and not overlapping each other, condyle formed obscurely ( Fig. 13 , 21 ). Maxillary palpi ( Fig. 11 : mp) obscurely 3-segmented. Labial palpi ( Fig. 11 : lp) 1-segmented. Prementum, maxillae, and postmentum undivided and fused with each other.

Pronotum about 1.1× as long as broad, about 1.4× as broad as head, obtusely angulate. Pro- to metanota each with egg-bursters ( Fig. 22 , 30 ), setae and markings absent ( Fig. 10 ). Prolegs conical, femora, tibiae and claws segmented ( Fig. 10 , 19 ).

Abdomen 9-segmented, widest at segment I and then narrowing posteriorly. Urogomphi short, pointed apically, setae absent ( Fig. 23 ).

Description of second instar (larva after the first molt) ( Figs 14–16 ). Measurements in mm (n = 1). BL: 1.19; BW: 0.2; HL: 0.14; HW: 0.12; UL: 0.18.

Body unpigmented and translucent, soft, rather rugose, oblong. Yolk presented immediately after molt, then consumed. Head capsule subquadrate, about as long as broad and flattened above, frontal arm and epicranial stem distinct; with 17 or 18 pairs of setae and 4 pairs of pores on epicranial plates, with 8–10 pairs of setae and 1 or 2 pairs of pores on frons ( Fig. 15 ). Five visible stemmata, arranged as in first instar. Antennae ( Fig. 15 : an) visible 3-segmented; segment II with conical sensorium and 2 long setae, segment III with a long and 3 short setae. Labrum about 4.0× as broad as long, with 6 long setae in middle and 8 short setae on labro-epipharyngeal margin. Maxillary palpi ( Fig. 16 : mp) 3-segmented, obscurely visible, segment II with seta and segment III with sensilla. Labial palpi ( Fig. 16 : lp) 2-segmented, obscurely visible, segment II with pore and segment III with sensilla. Prementum subtrapezoidal, with 2 pairs of setae and a pair of pores. Maxillary stipes and postmentum distinctly visible, the former bearing 7 pairs of setae and the latter with 5 setae and 3 pores. Cardo invaginated behind stipes ( Fig. 16 ).

Pronotum about 1.3× as long as broad, about 1.4× as broad as head, dorsum unpigmented, with pair of glandularium, 14–21 pairs of setae. Meso- and metanota subequal in width, each with a pair of glandularium in middle; former with 7–8 pairs of setae; latter with 9–11 pairs of setae. Prolegs long; femur with 6 setae, tibiotarsi with 5 setae, claw with 1 short seta ( Fig. 14 ).

Abdomen 9-segmented, slightly narrowed anteriorly and posteriorly, abdominal tergites I–VIII each usually with 12 pairs of setae and pair of glandularium dorsally. Urogomphi subparallel, apices suddenly recurved, with 11 pairs of setae and 5 pairs of pores ( Fig. 14 ).

Seasonal abundance. In temperate regions of Japan, many males and females were found in the middle of April, however males were hardly found since around May 2, and females could not be found on May 20 in the lowland area of Shizuoka city. Mature larvae and pupae were found in early April in the field. Eggs were laid from early until middle of May.

Biology and larval morphogenesis ( Figs 17–30 , Tables 1 –2). Malachius prolongatus inhabits bushes and thickets near inland water areas. Eggs are laid under bark of dead branches of Pueraria lobata and leaf sheats of dead Miscanthus sp. in captivity ( Fig. 24 ). At each egg site, 1– 40 eggs were laid. Oviposition was observed twice per female. Second oviposition began 11 days after the first one (Table 2). Eggs were not covered by anything. Embryos grew larger in the chorion; eggs were filled to bursting with embryos immediately before egg burst.

Egg burst and egg hatch begins 9 or 10 days after oviposition (Table 2). The eggs of the same clusters did not all begin to burst at once. Chorion bursts around the larval head to thorax and the larvae partly wriggle out, but remain largely hidden in the chorion for 2 days ( Fig. 25 ). They were inactive and non-feeding; however, they consumed water and wriggled the upper half of the body to expose themselves to the sun. Some body parts remained in the foetomorphic state, the whole body was translucent and flabby, cephalic suture and setae were unformed, mandibles were short and not overlapping each other, condyles were vestigial, they had an extra stemma than normal, urogomphi were short and vestigial and prolegs were short and conical ( Figs 17–23 ) ( Table 1).

First molt generally began two days after hatching (n = 89) ( Fig. 26 ). Egg bursters (peb, meb) are present in the cuticle of the first instar ( Fig. 30 : peb, meb).After the first molt, larvae were immediately active, walked on dead branches and consumed the nymphs of aphids which were provided. The yolk which is still present immediately after the first molt, was completely digested in second instar. Larval morphs drastically changed by the first molt. Cephalic and pronotal setae formed; antennae, maxillary and labial palpi were distinctly segmented; egg bursters were absent; mandibles, condyle and urogomphi were completely formed. The head capsule, the tip of mandibles and urogomphi became slightly pigmented ( Table 1). The molted cuticle of the first instar larva remains adhered inside of the empty chorion ( Fig. 26 ).

Second molt began about 5 days after the first molt. After the second molt, larvae were also very active. They stayed on the bead branches and consumed small arthropods. Mature larvae probably overwinter, pupate in early spring within dead Miscanthus stems, and adults emerge in the spring in the lowland area of Shizuoka city. ( Fig. 28 ). Number of larval instars is however still not known. The morphology of mature (= likely last instar) larvae was described by HAYASHI & TAKENAKA (1959) ( Table 1).

The adults are aggressive and prey on many small insects, as well as on each other. While in captivity, they also consume the small insects provided and the pollen of the above plants ( Fig. 27 ). They prey on nymphs of aphids very well, but were in distress to prey on the fast- -moving, jumping plant lice and thrips. They were often parasitized by nematodes ( Fig. 29 ).

Mating was observed at the end of April. For this species, the male and female contact each other with their mouthparts ( TAGO 2004). This is possibly a precopulatory behavior. For the related species Malachius bipustulatus (Linnaeus, 1758) , it is known that the female contacts the frons of the male (excitator) with her labial palpus. It is suggested that a secretion from the excitator is used for precopulatory behavior ( MATTHES 1962). There is a possibility that the female of M. prolongatus also contacts the male glandularium on the frons ( Fig. 6 ) by the labial palpus or a tuft of hairs on the gula ( Figs 7, 9 ).

It is conceivable that females oviposit at least twice from early through late May. They require about 11 days from first to the second oviposition (Table 2).

Remarks. HAYASHI (1974) described an interesting case of the oviposition of M. prolongatus on a dipteran larva, but it was probably accidental. The closely related species Axinotarsus pulicarius (Fabricius, 1775) lays 10– 30 eggs per oviposition per female ( EVERS 1960).

Figures

Figs 1–9. Illustrations of Malachius (Malachius) prolongatus Motschulsky, 1866.male (1–5), sexual dimorphisms in adult (6–9). 1 – habitus; 2 – 8th sternite in ventral view; 3 – 8th tergite in dorsal view; 4 – endophallus in lateral view with extrusive gonoporal piece; 5 – spicular fork; 6 – male head in dorsal view with a tuft in lateral view; 7 – ditto, in ventral view; 8 – female head in dorsal view; 9 – ditto, in ventral view. Scales = 1.0 mm:A (1), B (2–5), C (6–9). Abbreviations: gl – the aggregation of glands; gp – gonoporal piece; is – intarnal sac; sc – sclerite; tf – tuft of hairs.

Figs 10–16. Early instars of Malachius (Malachius) prolongatus Motschulsky, 1866. 1st instar (10–13), 2nd instar (14–16). 10 – habitus in lateral view; 11 – head in ventral view; 12 – antenna in ventral view; 13 – right mandible in ventral view; 14 – habitus in lateral view 15 – head in dorsal view; 16 – mouth parts in ventral view. Scale A= 0.1 mm:(10), 0.04 mm:(11), 0.015 mm: (12–13), Scale B = 0.1 mm: (14), 0.02 mm: (15), 0.01 mm: (16).Abbreviations: an – antenna; lp – labial palp; md – mandible; mp – maxillary palp.

Figs 17–23. Photographs of first instar of Malachius (Malachius) prolongatus Motschulsky, 1866. 17 – habitus in ventral view; 18 – ditto in ventral view; 19 – ditto in lateral view; 20 – maxillary and labial palpi; 21 – mandibles; 22 – egg bursters; 23 – urogomphi.Abbreviations: an – antenna; cr – chorion; L1 – first instar larva; lb – labrum; lp – labial palp; md – mandible; meb – eggburster of mesonotum; mp – maxillary palp; peb – egg-burster of pronotum; pl – proleg; st – larval stemma.

Figs 24–30. Photographs of Malachius (Malachius) prolongatus Motschulsky, 1866. 24 – eggs; 25 – hatching; 26 – first molting; 27 – adult; 28 – pupa; 29 – adult parasited by nematode (indicated by an arrow); 30 – chorion and cuticles first molted.Abbreviations:cr – chorion; ct – cuticle; L1 – first instar larva; meb – eggburster of mesonotum; peb – egg-burster of pronotum.