Descriptions of the last instar larva and pupa of Ora depressa (Fabricius) (Coleoptera: Scirtidae)

ARCHANGELSKY, MIGUEL; LIBONATTI, MARÍA LAURA; MICHAT, MARIANO CRUZ

Luján de Cuyo

Congreso; X Congreso Argentino de Entomología; 2018

IADIZA-CONICET y Fac. de Cs. Agrarias

Ora is a genus of saltatorial marsh beetles, presently represented by ca. 60 species worldwide. Preimaginal stages of this genus are very poorly known. Only the mature larvae of two species and the pupa of one species have been described so far. In this contribution we describe for the first time the last instar larva and pupa of Ora depressa, providing illustrations of diagnostic characters and information on its biology. Larvae were collected in Pre-Delta National Park, Entre Ríos Province (March 2012) and Antonia Ramos Research Centre, Misiones Province (November 2013), and reared to adults in the laboratory. Larvae were either cleared in lactic acid (not necessary in the case of exuviae), dissected, mounted on glass slides with polyvinyl?lactoglycerol, and observed under a compound microscope, or dehydrated in an ethanol series, treated with hexamethildisilazane and examined using scanning electron microscopy. Last instar larva of O. depressa exhibits the characters traditionally recognized as diagnostic of the genus: tip of mandible blunt and forth segment of maxillary palpus as long as third segment. Ora depressa is characterized by: body elongate, widest at metanotum, brownish testaceous with several brown spots, dorsal surface mostly covered with numerous spatulate setae and also several hair-like, peg-like and pore-like sensilla arranged in a specific pattern, and femur and tibiotarsus bearing a row of natatorial setae. Ora depressa can be distinguished from the other known species of the genus by: lateral margins of clypeolabrum diverging anteriorly, lobes of clypeolabrum as long as wide, presence of two fields of bristles on mandibles, serrate bristles on keel sclerite of hypopharynx, comb plate of hypopharynx bearing 5-6 teeth, and anterodorsal margin of tergite 9 produced medially. Pupa of O. depressa differs from that of O. okinawana mainly in the absence of pronotal spines and the place where pupation occurs. Ora depressa pupates underwater, hanging from water?s surface thanks to the presence of hydrophobic setae along lateral margins of pronotum. Chaetotaxy is a very useful source of characters in larval taxonomy, as has been shown for other aquatic beetles.