Intybia takaraensis, (Nakane, 1955)

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 : 624-626

INTYBia TakaraeNsis (Nakane, 1955)

Mature Instar

( Figs. 18 , 20, 22, 25 )

Larval Coloration. Head capsule light brown except black posterior half and black around stemmata, mandibles light brown except dark brown anterior margin, antennae and mouthparts light brown; legs translucent except black lateral and posterior margin of femora; thoracic tergites and abdominal tergites IV, V, VI, and VIII white with dark purple markings in middle, tergites I, II, III, and VII dark purple; urogomphi black ( Figs. 14 , 18 ).

Larval Structure. Head capsule suboblong; frons with about 18 pairs of setae; epicranial plate with about 14 pairs of setae and 13 pores ( Fig. 20 ). Clypeus transverse, weakly pigmented. Labrum about 3.3 times as broad as long, 4 median and 4 thick short setae along labro-epipharyngeal margin arranged as figured and 10 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 and 3 setae; III with 3 short setae, 1 long seta and pore ( Fig. 23 ). Mandibles each with distinct teeth on cutting edge; ventral margin ridged and provided with a single tooth, which is cleft at apex; external face with 3 long setae and 1 short seta ( Fig.25 ). Maxillary palpi 3-segmented, palpomere II with 3 short setae along apical margin, III slightly longer than preceding, with 1 pore on middle ( Fig. 22 ). Labial palpi 2-segmented, palpomeres subequal in length; palpomere II with 1 pore at middle ( Fig. 22 ). Maxillary stipes and postmentum distinctly visible, the former bearing 17 setae, the latter 5 pairs of setae and 2 pairs of setae on peripheral membrane ( Fig. 22 ). Cardo invaginated behind stipes, only basal border with a seta visible ventrally ( Fig. 22 ).

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. 18 ). Pronotum about 1.5 times as broad as long, about 1.3 times as broad as head, with 1 large medusoid-shaped strongly pigmented area on the middle, bearing 4 pairs of long setae on the antero-lateral portions, 2 pairs of long setae on the basal portion, 5 pairs of long setae and 1 pair of glands on the middle ( Fig. 18 ). Meso- and metanota subequal in width, with 1 or 2 pairs of strongly pigmented areas on the antero-lateral portion toward middle portion ( Fig. 18 ). Mesonotum bearing 1 pair of long setae on the antero-lateral portions, 6 pairs of long setae on the basal portion, and 1 pair of setae and glands at the middle. Metanotum bearing 2 pairs of long setae on the antero-lateral portions, 2 pairs of long setae on the basal portion, 2 pairs of long setae and 1 pair of glands at the middle ( Fig. 18 ).

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 with short duct and balloon-like sac at the middle, with 2 pairs of long setae and 1 pair of glands on lateral portions ( Fig. 18 ). Urogomphi subparallel, strongly curved upwards, bearing numerous long setae and 1 pair of glands on the antero-lateral portion ( Fig. 18 ).

Legs elongate, slender. Claw slender, with a short seta ( Fig. 18 ).

Measurements in mm (n = 1). BL: 4.55; BW: 0.90; HL; 0.58; HW; 0.50; PL: 0.43; PW: 0.65; TL: 0.30; UL: 0.53.

Notes. The body coloration is a patchy pattern of dark purple and white in dorsal view and is well camouflaged on sand grains ( Fig. 15 ).

Within the tribe Apalochrini , the mature larval morphology of members of the genus Collops Erichson, 1840 and the genus Laius have been described thus far. The larva of Collops nigriceps (Say, 1823) differs from those of the genus Intybia in the bifid apices of the urogomphal rami (Böving and Craighead 1931) and those of the genus Laius differ in the monochrome dark brown head capsule and the strongly pigmented thorax and abdomen with short, dense setae in the mature instar (Asano and Kojima 2009; Satô 1964; Yoshitomi 2014).

Larval Development and Bionomics. Adults were collected mainly from the leaves and ears of cogon grass, green foxtail, murainagrass, and rarely from reeds in the estuary and coast using a sweep net. Mating behavior was observed during the month of May, during which the male mounted on the back of the female. When disturbed by the author’s presence, the female became active and dragged the male behind her ( Fig. 10 ). In captivity, an interesting mating behavior was observed. When a male located a female, he remained still, waiting for the female and repeatedly inflating and deflating the small protuberances of his third antennomeres ( Fig. 8 ). He oriented and thrust his third antennomeres forward upon approach of the female ( Fig. 9 ). Sometimes the females made contact with these antennomeres using their mouthparts and other times they left without interaction. This is perhaps a form of precopulatory behavior, wherein the males secrete a substance from their antennomeres or even imitate a small arthropod. Adults lived particularly long lives, reaching a maximum of 142 days in captivity, feeding only on dead chironomid larvae. Oviposition was observed throughout June and on a single occasion during September. During each oviposition, 5– 11 eggs were laid. In captivity, each egg was inserted under the leaf epidermis, between the leaf veins of dead or wilted leaves of cogon grass ( Figs. 11, 12 ). The eggs hatched about six or seven days after oviposition, and underwent two instars of foetomorphic larval stages similar to I. pelegrini . The first molt generally began one day after hatching. Second instar larvae were also foetomorph, being inactive and non-feeding, and they remained between the leaf veins for three days ( Fig. 13 ). The first larval cuticles that were shed contracted at the bottom of the chorion. The second molt generally began four days after hatching. Once the third instar larvae emerged from the chorion completely, they began walking and feeding, and these larvae consumed dead chironomid larvae that were provided for them; it is believed that they feed on small cohabiting arthropods in nature. Thrips (Thysanoptera) and larvae of flies ( Diptera ) and of skipper butterflies ( Lepidoptera : Hesperiidae ) were found in the vicinity of the roots of cogon grasses growing in the study area. Larvae that hatched during the middle of July became final instar on 3 September and pupated on 14 September.An adult female that eclosed on 20 September lived for 142 days in captivity. A middle instar larva was collected in the field on 24 May 2019. It pupated on 6 July 2019 in captivity ( Fig. 16 ) and emerged as an adult male on 13 July 2019. However, another specimen of a middle instar larva that was collected on 7 October 2019 (which probably hatched in late summer) grew into a final instar until December and then passed the winter in this state, pupated on 6 May 2020 and eclosed as an adult male on 16 May 2020. In addition to these specimens, further middle instar larvae were collected from a nearby container port terminal. In this area, I. takaraensis inhabits green foxtail growing in cracks in the pavement.

Seasonal Occurrence. Adults were collected from 24 May to 20 September in the field ( Table 3). However, warm conditions appropriate for collection occurred only between 11:00am and 1:00pm during early summer. Mating was observed on 27 May. Oviposition was observed throughout the period between 5 June and 3 July, along with a single oviposition on 26 September. Larvae were collected from 24 May to 23 October in the field ( Figs. 14, 15 ). In captivity, the larvae that hatched during early summer could become adults during the summer up to early fall of the same year; however, the larvae hatched during late summer passed the winter in the larval state, then pupated and eclosed during May of the following year.

Notes. Intybia niponica and Laius asahinai Nakane, 1955 also have two foetomorphic instars, which have already been described (Asano 2013; Asano and Kojima 2013).

In general, adults of Intybia species are long-lived, with a maximum longevity of over four months in captivity. The specimens which eclosed in captivity were given only dead chironomid larvae. The adult of Laius , belonging to the same tribe ( Apalochrini ), was also reported to be carnivorous ( Setoyama et al. 2020). Mayor (2002) mentioned “Most adult Melyridae are, at least potentially, polyphagous, feeding on both plant and animal material.Many feed preferentially on pollen of various cone bearing and/or flowering plants, gathering in rather large, inconspicuous aggregations”; however, plant material might not be the primary food source for these two genera.

Most I. takaraensis were collected from communities of mid-sized grasses, which consisted almost entirely of cogon grass and green foxtail. In contrast, I. pelegrini may be highly dependent on tall grasses. The mid-sized grasses are smaller in size and inhabit drier areas compared with the tall grasses ( Hattori et al. 1994; Kamata and Ogura 2006). Nevertheless, it is thus assumed that I. takaraensis tends to prefer mid-sized grasses since they lay eggs through a peculiar ovipositing behavior on these plants, and all the larvae of this species were collected from these grasses. It is assumed that this preference has eased competition with I. pelegrini . This presumed niche partitioning of these species needs to be examined in detail in future.

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. 8–16. Larval development of Intybia takaraensis. 8–9) Precopulatory behavior; 10) Mating; 11) Eggs oviposited between the leaf veins of dead leaf; 12) Ditto, pellicle removed; 13) Second instar larvae; 14) Sixth instar larva; 15) Sixth instar larva on sand grains; 16) Pupa.