Pyrearinus pumilus (Candèze, 1863)

Rosa, Simone Policena, Mariano, Raone Dos Reis, Viviani, Vadim R. & Costa, Cleide, 2020, Morphology of immature stages of Pyrearinus pumilus (Candèze, 1863) (Coleoptera: Elateridae: Pyrophorini): the click beetle responsible for the luminous canga caves in the state of Pará, Brazil, Zootaxa 4778 (3), pp. 561-570 : 563-568

publication ID	https://doi.org/ 10.11646/zootaxa.4778.3.7
publication LSID	lsid:zoobank.org:pub:F0D3226B-1728-4213-AAF6-F32F4FEB8E27
DOI	https://doi.org/10.5281/zenodo.3848000
persistent identifier	https://treatment.plazi.org/id/03A387C9-5715-FFD2-FF0B-903713987019
treatment provided by	Plazi
scientific name	Pyrearinus pumilus (Candèze, 1863)
status

Treatment

Diagnosis of mature larva. Body weakly sclerotized, mostly pale yellow, except anterior margin of frons, mandibles, spiniform setae on legs, spines and tubercles on segments IX and X dark brown to black (Figs 2; 4A); tergite IX with four pairs of spiniform tubercles along lateral margins and one pair at middle ( Figs 3L,M View FIGURE 3 , 4B View FIGURE 4 ); segment X with a row of 5–6 spine-like setae laterally.

Description of larva. Mature larva (Figs 2, 3, 4A,B, 5A,B). Length: 15–20mm. Body (Figs 2, 3A, 5A,B) elongate, parallel-sided, almost cylindrical; tegument pale yellow, except for anterior margin of frons and mandibles dark brown to black; antenna brown.

Head ( Figs 3B,C View FIGURE 3 , 4A View FIGURE 4 ) prognathous, subparallel-sided,1.0–1.2 times as wide as long, sparsely punctate, with regular longitudinal row of setae along lateral and posterior regions, three pairs of small setae at posterolateral margin. Posterior margin curved. Epicranial stem absent. Frontal arms lyriform; one stemma on each side. Nasale with three teeth, with one stout and two fine setae between each tooth; adnasalia as long as the nasale, with three setae. Antenna ( Figs 3E,F View FIGURE 3 ) 3-segmented; basal antennomere with one seta ventrally and several short and long setae along distal lateral and dorsal parts; antennomere 2 sparsely setose, with conical sensorium ventrally, 3 times longer than wide; apical antennomere about 1/2 as long as antennomere 2, with one long seta and few stout and fine microsetae at apex. Mandible ( Figs 3 View FIGURE 3 G–I) gradually curved to apex, unidentate, ventrobasal surface with one seta, lateroventral margin with one seta, penicillus absent. Hypocephalic carina ( Fig. 3C View FIGURE 3 ) reaching 4/5 of head length in ventral view, with row of 5–7 setae. Ventral mouthparts forming maxillolabial complex ( Figs 3C,D View FIGURE 3 ); maxillae ( Fig. 3D View FIGURE 3 ) with cardines narrow and sinuous, contiguous to each other at midline, stipites elongate sparsely setose along lateral border, setae denser on anterior corner; palp 4-segmented, palpomeres with sparse setae along apical border, apical palpomere with very small basiconic sensilla; galea ( Fig. 3J View FIGURE 3 ) 2-segmented, apex densely covered with very small basiconic sensilla and one long seta. Postmentum ( Fig. 3D View FIGURE 3 ) triangular widened anteriorly with row of 2–3 setae anterolaterally and pair of setae posteriorly; prementum with two lateral setae at midlength and two setae apically, ligula very short and rounded apically; labial palp 2-segmented, widely separate, sparsely setose.

Thorax (Figs 2A, 3A). Prothorax 0.8 times as long as meso– and metathorax combined; meso- and metathorax subequal. Pronotal lateral margin with row of six long setae, each lateral half of dorsal surface with three setae anteriorly, one seta at midlength and three setae posteriorly. Meso- and metanotum with two long setae on lateral margin, each lateral half of dorsal surface with two setae near anterior margin and three setae near posterior margin. Prosternum triangular, each side with two setae near anterior margin and one seta posteriorly; postgular region with four pairs of setae (S1, S2, S3 and S4), one small transverse sclerite (P2) externally to S1, one sclerotized transverse line (P1) medially between S1, and very small sclerite (P4) anteriorly to S1. Meso- and metasternum with one lateral seta; mesothoracic spiracle in lateroventral position. Leg ( Fig. 3K View FIGURE 3 ) stout, trochanter, femur and tibia with spiniform setae ventrally; shorter, fine and sparse setae dorsally; pretarsus slender, as long as tibia with two setae lying side by side at base.

FIGURE. 2. Habitus of Pyrearinus pumilus mature larva. (A) dorsal view, (B) ventral view.

Abdomen. Terga I–VIII with each side (Figs 2A, 3A) with pair of setae near the anterior margin, four setae near posterior margin, and spiracles near anterior margin. Sterna I–VIII (Fig. 2B) with pair of lateral longitudinal depressions, each side with three short setae on anterior corner, one at midlength and three on posterior corner; lateral margin with log setae. Segment IX ( Figs 3L,M View FIGURE 3 , 4B View FIGURE 4 ) as long as VIII, 1.2 times longer than wide, posterior margin notched at middle forming urogomphi; dorsal surface setose on posterior 2/3, with pair of parasagittal tubercles; two tubercles on lateroposterior margin, and two tubercles at apex of each urogomphus; tubercles spine-like and bordered by 1–3 setae; lateral margin and ventral surface densely covered with long setae. Segment X ( Fig. 3M View FIGURE 3 ) ventral; near anal opening: row of short setae along the posterior margin, pair of large anal hooks, row of 5–6 spinelike setae laterally, and fine, longer setae along anterior margin.

Abdomen. Terga I–VIII with each side (Figs 2A, 3A) with a pair of setae near the anterior margin, four setae near the posterior margin, and spiracles near anterior margin. Sterna I–VIII (Fig. 2B) with a pair of lateral longitudinal depressions, each side with three short setae on the anterior corner, one at midlength and three on posterior corner; lateral margin with log setae. Segment IX ( Figs 3L,M View FIGURE 3 , 4B View FIGURE 4 ) as long as VIII, 1.2 times longer than wide, posterior margin notched at middle forming urogomphi; dorsal surface setose on posterior 2/3, with a pair of parasagittal tubercles; two tubercles on lateroposterior margin, and two tubercles at apex of each urogomphusi; tubercles spinelike and bordered by 1–3 setae; lateral margin and ventral surface densely covered with long setae. Segment X ( Fig. 3M View FIGURE 3 ) ventral; near the anal opening: a row of short setae along the posterior margin, a pair of large anal hooks, a row of 5–6 spine-like setae laterally, and fine, longer setae along anterior margin.

Description of pupa. Pupa ( Figs 5C,D View FIGURE 5 ) 10–12 mm length; adecticous, exarate, body smooth, glabrous, creamwhite. Head directed ventrally; eyes shortly inserted into prothorax; pronotum with two pairs of cuticular prolongations: one erect pair at anterior margin and one curved pair at tips of posterior angles; one pair of very small parasagittal spines on posterior margin. Abdomen with laterodorsal functional spiracles near anterior margin of segments I–VII, tergite IX with pair of bifurcated urogomphi, covered with stout microsetae; inner rami of each urogomphus longer, with one seta.

Material examined. BRASIL. Pará. Canaã dos Carajás, Caverna de Canga. 23.XI.2016, V. Viviani col., 1 mature larva (L5) fixed on 2.IV.2018 ( MZUSP) ; 1 larval exuvia and 1 mature larva (L3) fixed on 4.VII.2018 ( UNIFEI) ; 1 larval and 1 pupal exuvia, 1 adult male (L12) ( UNIFEI) fixed on 23.X.2018; 1 larval and 1 pupal exuviae, 1 adult female (L1) fixed on 26.IV.2018 ( UNIFEI) ; 1 larval exuvia and 1 pupal exuvia fixed on 20. VI.2018 ( UNIFEI) , 1 adult female (L8) fixed on 18.X.2018 ( UNIFEI) .

Biology and bioluminescence. Some of the biological observations made in 2014 and 2015 had already been reported ( Viviani & Amaral, 2016). Here we point out some additional ones from an expedition in 2016. Larvae of P. pumilus were found in crevices on the clayish walls, and the bottom of the caves, exposing their bioluminescent thorax ( Fig 5A,B View FIGURE 5 ). There were patches with several larvae. However, they could be found spread out in different depths of the tunnels, even far from the entrances. At the end of the day, several tiny mosquitoes could be found coming in and out the entrance of the cave, suggesting that they could be putative flying prey attracted by the larval lights inside the cave. Adult females could be found inside and mainly at the entrance of the cave, whereas one male was found outside, suggesting that courtship and copula may occur outside the cave and that pregnant females may lay eggs inside the cave. However, more studies are necessary to understand the courtship and infestation by the larvae of the caves.

Larvae of P. pumilus displays green bioluminescence from a prothoracic luminous organ and several lateral luminous spots along the mesothorax, metathorax and abdominal segments I–VIII and a dorsal luminous spot in the IX abdominal segment ( Figs 5A,B View FIGURE 5 ). Visually, the bioluminescence color was green, similar to that observed for P. termitilluminans larvae that live in Cerrado termite mounds. The uncorrected luminescence spectrum of P. pumilus is in the green region with the peak at 550 nm ( Fig. 6 View FIGURE 6 ). The uncorrected luminescence spectrum of P. termitilluminans larvae, measured with the same equipment has a peak at 546 nm. Luminescence of the prothoracic organ is easily stimulated upon touch, such as in the case of most other luminescent click beetle larvae, and may suggest a defensive function, besides the prey attraction. Larvae expose their luminescent prothorax outside crevices in the clayish walls and eventually on the ground and near the roof. V. R.V. had observed bioluminescent activity in the dark caves already earlier in the afternoon, around 3:00 PM in early November at temperatures ranging from 24–26 degrees C. The adult female and male display the two typical luminescent vesicles on the pronotum which produce greenish light. In the laboratory, larvae always stayed buried in the substrate and moved in a circular tunnel digging along the border of the glass. They only emitted light using the prothoracic luminous organ after being disturbed.