Hybolabus amazonicus Voss, 1925

Vanin, Sergio Antonio & Bená, Daniela de Cássia, 2020, Description of larva and pupa of the weevil Hybolabus amazonicus Voss (Attelabidae: Attelabinae), a leaf roller on Brazil nut (Bertholletia excelsa), Papéis Avulsos de Zoologia 60 (3), pp. 1-8 : 2-6

Hybolabus amazonicus Voss, 1925

( Figs. 1 B-5E)

Description of last larval instar ( Figs. 2 A-4D): About length: 5 mm; head capsule width about 1.8 mm; body C-shaped, subcircular in cross section, with sparse, short and fine setae, not placed on tubercles.

Head ( Figs. 2 A‑2C): Prognathous, moderately retracted, sclerotized, yellowish brown; head capsule slightly wid- er than long, lateral margins parallel-sided. Epicranial suture distinct, approximately 0.65 times as long as head capsule. Frontal suture distinct, complete, weakly curved, V-shaped. Median endocarina present, about 0.15 times as long as head capsule. One stemma present on each side (stm) ( Fig. 3B). Hypopharyngeal bracon absent ( Fig. 3C). Antennae exposed ( Figs. 2B, 3B), two segmented; basal segment ring-like with 4 medial setae; distal segment conical and about two times longer than wide; base of antennae with one conical sensillum and one small rounded sensillum. Head capsule ( Figs. 2B, 2C) with five pairs of minute posterior epicranial setae (pes1‑5), almost aligned vertically; five pairs of dorsal epicranial setae (des1‑5); five pairs of subequal frontal setae (fs1‑5); three pairs of lateral epicranial setae (les1‑3) with similar length; two pairs of ventral epicranial setae (ves), ves2 slightly longer than ves1. Epistomal and frontoclypeal sutures slightly arcuate. Clypeus ( Fig. 3A) transverse, lateral margins converging anteriorly to straight anterior margin, with two pairs of subequal clypeal setae (cls1‑2), and one pair of basal sensilla. Clypeolabral suture distinct. Labrum ( Fig. 3A) transverse, anterior margin trilobed, with four pairs of labral setae (lrms1‑4) and one pair of basal sensilla. Epipharynx ( Fig. 3C) with one pair of anteriomedian setae (ams), three pairs of anterolateral setae (als1‑3), and three pairs of median spines (ms) between vertical labral rods, anterior sensilla larger than posterior ones; labral rods (lr) long, extended backwardly beyond epistoma, H-shaped, arms curved; epipharyngeal sensory spots absent. Maxillae ( Figs. 3D, 3E) with cardo transverse and slender, cuneiform; stipes elongate with one seta on dorsal side and two setae on ventral side; mala rounded, slightly inward extended, without spines, with about 15 marginal dorsal spatulate setae more or less aligned along anterior outer margin ( Fig. 3E); maxillary palpus three-segmented, proximal palpomere transverse, wider than distal segments,with one seta and two sensilla, medial palpomere unisetose, distal palpomere with some minute apical sensilla. Labium ( Fig. 3D): labial palpi two-segmented, palpomeres elongate and with similar length, basal palpomere slightly wider than distal one, distal palpomere with ventral sensillum; prementum with one pair of setae and one pair of sensilla close to palpus insertion; submentum with three pairs of setae, posterior pair longest; ligula short, not reaching tip of labial palpi, with 2 pairs of setae and one pair of sensilla. Mandibles symmetrical ( Figs. 3F, 3G), stout, apically bidentate, cutting edge dentate; dorsally with two sensilla and two aligned setae (mds), hind seta slightly longer than distal one.

Thorax ( Figs. 2A, 4A): Prothorax narrower than meso-, and meso- narrower than metathorax. Prothorax with patches of short setae; pedal lobe with six pedal setae (pdas1‑6); ventropleural lobe with two setae (vpls1‑2); each side of meso- and metathorax with similar number of setae: prodorsum with two prodorsal setae (prs), postdorsum with eight dorsolateral setae (dls1‑8); pedal lobe with three setae (pdas1‑3); ventropleural lobe with two setae (vpls1‑2). Thoracic spiracle in intersegmental fold, bicameral ( Fig. 3H), slightly oblique, air-tubes with nine annuli.

Abdomen ( Figs. 2A, 4B, 4C): With eight pairs of lateral spiracles ( Figs. 3I, 3J); spiracles bicameral, air-tubes backwardly directed and with nine annuli; segments I-VIII with two dorsal folds; segment IX without dorsal fold, broadly rounded in lateral view; segment X reduced, ventrally directed, anus subterminal. Segments I-VII with similar chaetotaxy ( Figs. 4B, 4C): prodorsum with 12 setae on each side (prs), nine of which more or less aligned and forming a transverse row; postdorsum with 10 setae on each side (pds), nine of which more or less aligned and forming a transverse row; spiracular area asetose; dorsopleural lobe with two setae (dpls1‑2); ventropleural lobe with three setae (vpls1‑3); laterosternal lobe with two setae (lsts1‑2); mediosternal lobe with two setae (msts1‑2). Chaetotaxy of segment VIII similar to segments I-VII, but with less prodorsal setae (prs).

Alimentary canal ( Fig. 4D): Lacking mycetomes; posterior ventriculus (pov) three coiled, with about 14 short rod-like gastric caeca (gcc), nearly contiguous, arranged in two more or less aligned rows, located on either side of median ventricular coil. Six cryptonephric Malpighian tubules, not thickened, arranged 3 + 3.

Description of pupa ( Figs. 5 A-5D): About length: 3.2 mm. Adecticous and exarate. Coloration cream-colored, with short stiff setae. Head completely covered by pronotum in dorsal view; each side with one supra-orbital seta (sos) and one orbital seta (os) located near inferior margin of eye; rostrum broad, wider than long, lateral sides slightly enlarged apicad, apex nearly straight; rostrum with one pair of short post antennal setae (pas) and one pair of rostral setae (rs). Prothorax trapezoidal, lateral margins sinuous; anterolateral margin with a row of nine setae (ls) on each side; posterolateral margin with a row of 10 setae (pls) on each side. Mesothorax with two transverse rows of six anterior and 14 posterior erect ter- gal setae, rows interrupted at middle. Metathorax with two transverse rows of four anterior and 12 posterior tergal setae, rows interrupted at middle. Each leg with two femoral setae (fes1‑2). Pterothecae extending up to third ventrite. Abdomen: segments I-VII with 20 tergal setae forming a transverse row located close to posterior margin; segments narrowed to posteriad; each side of segment VIII with a lateroventral seta and an acute posterio- lateral spine-like process (not articulated, pseudocerci or urogomphi); segment IX small. Segment X with gonotheca not divided in males ( Fig. 5D), with two oval bulges in females ( Fig. 5E). Seven annular spiracles placed at lateral sides of segments I to VII, visible at lateral view.

Material examined: BRAZIL: Acre, BR 317, km 75, III.1994 EMBRAPA, 6 adults, 1 leaf-roll ( MZSP). Amazonas,

Manaus, IV.1994, CPAA A. Pamplona col., 7 adults ; same locality, Rod. AM 010 , km 24.6, 06.VIII.1995, EMBRAPA CPAA Projeto Shift, Andreazze, R. col., 29 larvae (two of them dissected, mounted on 3 slides), 3 pupae ( MZSP) .

Host Plant: Bertholetia excelsa Humb. & Bonpl. (“castanheira-do-brasil”, “castanha-do-pará”, Brazil nut, Lecythidaceae ), a plant native to the Amazonian Region, is one of the most important non-timber producing tree species for sustainable extractive exploration of almonds ( Fig. 1F), used raw or roasted as human food, or for obtaining oils used in aviation and in the manufacture of cosmetics ( Garcia et al., 1997). The tree reaches 50 m in height ( Fig. 1A), the leaves are simple and glabrous ( Fig. 1E), reaching 25 to 35 mm long ( Lorenzi, 2000). Occurs mainly in Brazil, in the states of Amazonas, Acre, Rondônia, Pará and north of Mato Grosso, Tocantins and Maranhão, but there are also a few records from Bolivia, Peru, Venezuela, Guyana, Suriname and French Guyana ( Mori & Prance, 1990).

Biological notes on natural history: Fazolin & da Silva (1995) and Garcia et al. (1997) reported adults and larvae of H. amazonicus in the states of Acre and Amazonas, respectively, damaging old or new leaves of Bertholletia excels . Adults scrape the upper epidermis of the leaves and the continuous scraping activity by weevils can cause tears in the leaves. Females cut out the leaves near the apical third to the midrib or more ( Figs. 1B, 1C) and roll the cut part forming a cigar-like structure, called nidus ( Fig. 1D), inside which they lay from 1 to 20 eggs. Most leaf-rolls of H. amazonicus fall to the ground after being built and do not remain attached to the tree. The larvae feed on the leaf blade and use the leaf-roll as a shelter to turn into pupae. One to 14 adults were observed emerging from a single nidus. When the infestation is high, these weevils can cause serious damages, more pronounced in younger than older trees, due to the smaller foliage mass ( Garcia et al., 1997).

Garcia et al. (1997) also reported the occurrence of another species of Hybolabus , H. columbinus (Erichson, 1848) , also damaging leaves of the Brazil nut in the states of Acre and Amazonas. It should be noted that H.columbinus was previously only known from Colombia and Guyana ( Wibmer & O’Brien, 1986) and Garcia et al. (1997) published the first record of that species for Brazil. Hybolabus amazonicus and H. columbinus are very similar and share the reddish-brown antennae. They are easily distinguished by their body color: H. amazonicus has an entirely black body, whereas the elytra of H. columbinus are dark blue, and the venter is reddish-brown ( Voss, 1925).