Laius asahinai Nakane, 1955

Asano, Makoto & Kojima, Hiroaki, 2013, Description Of The Early Instars Of Laius Asahinai Nakane (Coleoptera: Malachiidae): First Discovery Of A Foetomorphic Larva In Malachiidae, The Coleopterists Bulletin 1, pp. 40-45 : 40-43

Laius asahinai Nakane, 1955

First instar ( Figs. 2, 3, 6, 9–14)

Description. Measurements in mm (n = 1): BL = 0.84; BW = 0.25; HL = 0.13; HW = 0.18; UL = 0.05. Body unpigmented and translucent, very soft, oblong oval in form, setae absent except on head capsule. Surviving yolk visible in midgut ( Figs. 2, 3, 9, 10), chorion still covering abdomen. Head: Subtrapezoidal, with 4 pairs of short setae dorsally and 1 pair of short setae along frontal margin; pore, frontal arm, and epicranial stem indistinct. Labrum fused with frons. Five stemmata obscurely visible, 3 arranged in transverse row anteriorly and 2 posteriorly. Antennae unsegmented ( Fig. 6). Mandibles vestigial, with about 5 sensilla at tip, fused with head capsule, and not overlapping each other ( Fig. 6). Maxillary and labial palpi unsegmented. Prementum, maxillae, and postmentum undivided and fused with each other. Hypopharynx visible, salivary glands visible through integument. Thorax: Pronotum about 2.0X as broad as long, about 1.3X as broad as head, obtusely angulate. Pro-, meso, and metanota each with 1 pair of egg bursters ( Fig. 14), without setae or markings ( Figs. 2, 9). Legs conical and unsegmented ( Figs. 3, 10). Abdomen: Nine-segmented, widest at basal 3 segments and then narrowing posteriorly. Urogomphi undeveloped, with slight slit in middle, setae absent ( Fig. 2). Internal anatomy: Esophagus ( Fig. 11), proctodeum ( Fig. 12), and trachea ( Fig. 13) visible through integument.

Second instar ( Figs. 4, 5, 7, 16)

Description. Measurements in mm (n = 1): BL = 1.14, BW = 0.26; HL = 0.11; HW = 0.15; UL = 0.06. Body unpigmented and translucent, soft, rugose except for legs, oblong ovate in form. Surviving yolk visible in midgut, old cuticle of first instar still covering abdomen. Head: Subtrapezoidal; pores indistinct, frontal arm and epicranial stem distinct. Frons with 11 pairs of setae; epicranial plates each with 10 setae. Five visible stemmata arranged as in first instar. Antennae 3-segmented, second segment with a conical sensorium and short seta, third segment with 5 setae. Labrum fused with frons ( Fig. 4). Mandibles protruding, fused with head capsule and not overlapping each other ( Fig. 7); external surface with 1 long and 2 short setae; condyle indistinct. Maxillary and labial palpi both 1-segmented, with apical sensilla. Stipes each with 6 setae. Postmentum with 4 pairs of setae. Prementum, stipes, and postmentum undivided and fused with each other. Hypopharynx invisible ( Fig. 7). Thorax: Pronotum about 2.3X as broad as long, about 1.4X as broad as head, obtusely angulate; dorsum unpigmented, with 1 pair of setae on antero-lateral portion, 4 or 5 pairs on basal portion, and 3 in middle. Meso- and metanota subequal in width. Mesonotum bearing 3 pairs of setae on antero-lateral portion, 7 pairs on basal portion, and 1 pair in middle. Metanotum bearing 2 pairs of setae on anterolateral portion, 5 pairs on basal portion, and 1 pair in middle ( Fig. 4). Legs conical, smooth and unsegmented ( Fig. 4). Abdomen: Nine-segmented, widest at third and fourth segments, slightly narrowed anteriorly and posteriorly, first to eighth segments each usually with 2 setae, of which 1 is short, and 5 pairs of short setae centrally. Urogomphi short, with several setae ( Fig. 4).

Remarks. Table 1 summarizes the morphological changes from completion of dorsal closure to larval maturation of L. asahinai . At about 10 days after oviposition, the embryo of L. asahinai completes dorsal closure. At this time, the tracheal system is formed. The larval cuticle, head capsule, and mandibles are unsclerotized and unpigmented. The antennae, maxillary palpi, labial palpi, and legs are unsegmented, and the labium is undivided and unpigmented. Yolk remains in the embryo which is covered with an embryonic cuticle (ec) ( Fig. 15).

Hatching begins about one day after dorsal closure. The first instar ruptures and removes the thin chorion using egg bursters ( Fig. 8). The larvae are inactive and nonfeeding, and remain at the site of hatching for one day. The embryonic cuticle disappears after hatching. Form of the first instar is identical to that of the embryo at completion of dorsal closure except for the existence of egg bursters and cephalic setae.

About one day after hatching, the first larval molt begins. The second instar is also inactive and non-feeding, with non-functioning mouthparts and legs. Morphological changes from the first to second instar are number of body setae increased, antennae segmented, maxillary and labial palpi 1-segmented, hypopharynx hidden behind labium, frontal arm and epicranial stem distinct, egg bursters absent, and urogomphi formed. However, other areas, such as the mouthparts and legs, remain incompletely developed compared with later larval morphs.

About four days after the first larval molt, the second larval molt begins. The third instar is immediately active, able to walk in search of prey. Morphological changes from the second to third instar are head capsule and urogomphi sclerotized and pigmented, other body parts pigmented, setae visible over entire body, legs segmented, mouthparts developed, and number of stemmata decreases from five to four. Normal larval morphogenesis was completed at this instar.

Laius asahinai pupates at least after the seventh larval molt, with the last instar being 10 times larger than the first. There are normally three to five instars in the order Coleoptera (Lawrence 1991) , and thus, the observance of eight instars in

5) Second instar, lateral view. eb = egg burster. Scale = 0.5 mm.

THE COLEOPTERISTS BULLETIN 67(1), 2013 43

this species is deemed exceptional among beetles. Supernumerary instars (e.g., a ninth instar) are known in some species of the related family Melyridae (Estrada and Jaime 1997) .

In Coleoptera , morphogenesis, including segmentation of mouthparts and legs and formation of setae and urogomphi, usually occurs during the latter part of the egg stage, from dorsal closure through hatching. However, in L. asahinai morphogenesis continues into the larval stage, reaching completion at the third instar. We suggest that the unique growth process is the result of interrupted morphogenesis some time after completion of dorsal closure.