Intybia pelegrini subsp. pelegrini, (Pic, 1910)

Asano, Makoto, 2021, Larval Structures and Bionomics of Two Species of the Genus Intybia Pascoe (Coleoptera: Melyridae: Malachiinae), The Coleopterists Bulletin 75 (3), pp. 617-628 : 618-624

INTYBia pelegriNi pelegriNi (Pic, 1910)

Mature Instar

( Figs. 17 , 19, 21, 23, 24 )

Larval Coloration. Head capsule light brown except dark brown ventral part and black around stemmata, mandibles light brown except dark brown anterior margin, antennae and mouthparts light brown; legs translucent; thoracic tergites orange except for white anterior and posterior margins, pronotum with dark brown markings in middle and meso-metanota with white markings posteriorly; abdominal tergites I, II, III, VI and VII maroon, tergites IV, V and VIII creamy white; urogomphi black ( Figs. 3 , 17 ).

Larval Structure. Head capsule suboblong; frons with about 28 pairs of setae and 1 pair of pores; epicranial plate with about 28 pairs of setae ( Fig. 19 ). Clypeus transverse, weakly pigmented. Labrum about 2.5 times as broad as long, 3 median and 2 short, thick setae along labro-epipharyngeal margin arranged as figured and 19 setae and 6 pores on antero-median region ( Fig. 24 ). Number of stemmata 4; anterior 3 arranged in transverse row. Antenna 3-segmented; antennomere II with conical sensorium, 3 setae and 1 pore; III with 1 long seta, 4 short setae and 1 pore ( Fig. 25 ). Mandibles each with distinct teeth on cutting edge; ventral margin ridged and provided with single tooth, which is cleft at apex; external face with 3 long setae and 1 short seta ( Fig. 24 ). Maxillary palpi 3-segmented, palpomere I with 1 short seta, II with 3 short setae along apical margin, III slightly longer than preceding, with 1 short seta and pore at middle ( Fig. 21 ). Labial palpi 2-segmented, palpomere I with 1 short seta and pore, II slightly longer than preceding, with 1 pore at middle ( Fig. 21 ). Maxillary stipes and postmentum distinctly visible, the former bearing 19 setae and 2 pores, the latter 7 pairs of setae and 1 pair of pores, and 5 pairs of setae on peripheral membrane ( Fig. 21 ). Cardo invaginated behind stipes, only basal border with 2 setae seen ventrally ( Fig. 21 ).

Thorax smooth and covered with short setae over entire surface, with 1 pair of glands with short duct and balloon-like sac on each segment ( Fig. 17 ). Pronotum about 1.8 times as broad as long, about 1.4 times as broad as head, with 2 pairs of pigmented areas as follows: larger, elongate medi- an pair and crescent-shaped lateral ones; pronotum bearing 4 pairs of long setae on the antero-lateral portions, 2 pairs of long setae on the basal portion, 3 pairs of long setae and 1 pair of glands (A) on the middle. Meso- and metanota subequal in width, each with 1 pair of pigmented areas near base. Mesonotum bearing 4 pairs of long setae on the antero-lateral portions, 1 pair of long setae on the basal portion, and 1 pair of glands (B) on the middle. Metanotum bearing 2 pairs of long setae on the antero-lateral portions, 1 pair of long setae on the basal portion and 1 pair of long setae and glands (C) on the middle.

Abdomen smooth and covered with short setae over entire surface, 9-segmented, widest at segments IV and V, thence slightly narrowed posteriorly; each segment with 1 pair of long setae and glands (D) on the middle, with 2 pairs of long setae and 1 pair of glands (E) on lateral portions. Urogomphi subparallel, strongly curved upwards, bearing numerous long setae and 1 pair of glands (F) on the antero-lateral portion ( Fig. 17 ).

Legs elongate and slender; femora and tibiae with dense setae. Claw slender, with a short seta ( Fig. 17 ).

Measurements in mm (n = 1). BL: 6.15; BW: 1.30; HL: 0.70; HW: 0.57; PL: 0.45; PW: 0.81; TL: 0.70; UL: 0.72.

Larval Development and Bionomics. Adults were collected from the leaves and ears of reeds using a sweep net at an estuary. Adults moved rapidly among the leaves of the reeds.Adult specimens were maintained in captivity, where the oviposition behavior of two females could be closely observed ( Fig. 6 ). These females continually oviposited from 4 June to 6 July at intervals of 4–8 days. The adult specimen A1 ( Table 1A) oviposited seven times, laying 74 eggs; clutch sizes were 5– 13 eggs (n = 7, mean = 10.5), and the periods of the egg stage were 6–7 days (n = 7, mean = 6.6). Specimen A2 ( Table 1B) oviposited six times, laying 69 eggs, clutch sizes were 6– 19 eggs (n = 6, mean = 11.5), and the periods of the egg stage were 6–7 days (n = 6, mean = 6.5). Eggs were not covered by any substance but were laid in clusters on the surface of the leaves or within leaf sheaths of the dead reeds ( Fig. 1 ). The abdomen of egg-bearing females was distended with eggs. Their abdominal tergites II–VI and sternites IV–VII ( Fig. 6 ) are mostly membranous and partly sclero- tized as small plates. One female, who lived until 7 August, made her final oviposition on 6 July. During the time period from 6 July to 7 August, this female did not oviposit, even though she was provided with a new mate because of the death of her first mate. In general, adults lived a long life, with a maximum longevity of 197 days in captivity, feeding only on dead chironomid larvae ( Fig. 7 ).

On average, eggs hatched 6.5 days after oviposition, and they underwent two instars of foetomorphic larval stage. The embryos grew much larger immediately before egg burst. The eggs of the same clusters began to burst simultaneously. The first instars ruptured and removed the thin chorion around the head and thorax using egg bursters, then the larvae partly wriggled free, but the abdomen remained hidden within the chorion for another day. The larvae were inactive and non-feeding during this stage. They did not walk; however, they had wriggled out sufficiently to expose the front half of the body to the air. The yolk was still present immediately after hatching. The first molt generally began one day after hatching, whereas the larval abdomen remained concealed in the chorion. Second instar larvae were also inactive and non-feeding and remained so for one or two days. The first larval cuticles that were shed contracted at the bottom of the chorion. The second molt generally began two or three days after hatching. Once the third instar larvae emerged from the chorion completely, they began walking and feeding. Third instar larvae consumed their unhatched siblings as well as dead eggs ( Fig. 2 ). The third molt occurred 23 days after hatching. Fourth instar larvae consumed dead chironomid larvae that were provided for them; it is believed that they feed on small cohabiting arthropods in nature. Scale insects (Hemiptera: Coccoidea), larvae of pyralid moths ( Lepidoptera : Pyralidae ), larvae of wasps (Hymenoptera) and flies ( Diptera ), thrips (Thysanoptera) and larvae of clerid beetles ( Coleoptera : Cleridae ) were found on dead reeds growing in the study area. Thereafter, the growth of the four larvae which fed only on dead chironomid larvae was closely observed ( Table 2), and these underwent five larval molts prior to pupation. Specimen L1 was oviposited on 1 July 2019 and became a final instar 43 days later. Specimen L2 was also oviposited on 1 July 2019 and became a final instar 45 days later; it then suddenly grew fat, pupated at 58 days and eclosed as an adult male on day 64. Specimen L3 was oviposited on 25 July 2019, pupated 49 days later and eclosed as an adult female on day 55. Specimen L4 was oviposited on 25 July 2019 and became a final instar 56 days later; however, pupation of this individual was delayed as the larva kept consuming food and grew fat, passing the winter in the larval state, pupated on 13 May 2020 and eclosed as an adult male on 23 May 2020. In the field, a mature larva was found on stems of dead reeds on 10 May ( Fig. 3 ). The pupal stage lasted for seven to ten days ( Fig. 4 ). Pupae were sexually dimorphic; male pupae had expanded third antennomeres with numerous spinae (sp) ( Fig. 5 ).

Seasonal Occurrence. Adults were collected between 21 May and 29 August in the field. Oviposition was observed continually between June and August. The period from oviposition to pupation was 49–293 days. In captivity, the larvae that hatched during early summer could become adults during the summer up to early fall of the same year; however, this species may pass the winter in the larval stage. Suzuki (2015) reported that a mature larva was found on the ground surface of a community of dead Phragmites ( Poaceae ) and Pueraria ( Fabaceae ) on 25 March in the field, and pupated on 4 May. In captivity, the larvae that hatched during summer passed the winter in the larval state, then pupated and eclosed during May of the following year.

Figures

Figs. 17–18. Larval habitus. 17) Intybia pelegrini pelegrini; 18) I. takaraensis. A–F show the locations of glands.

Figs. 19–25. Larval structures. 19) Head in dorsal view of Intybia pelegrini pelegrini; 20) Ditto of I. takaraensis; 21) Head in ventral view of I. pelegrini pelegrini; 22) Ditto of I. takaraensis; 23) Left antenna of I. pelegrini pelegrini; 24) Labrum of I. pelegrini pelegrini; 25) Left mandible of I. takaraensis.

Figs. 1–7. Larval development of Intybia pelegrini pelegrini. 1) Eggs; 2) Third instar larva feeding on siblings; 3) Sixth instar larva; 4) Pupa; 5) Pupal third antennomere; 6) Abdominal sternites of female; 7) Adults feeding on dead chironomid larva. sp = spinae; s4 = abdominal sternite VI.