Bioacoustics of Nicagus obscurus

Last instar larvae were 17.5 mm long, maximum width of head capsule 2.4 mm , width across dorsum of 2nd abdominal segment 2.9 mm . Body C­shaped; cranium and clypeus pale yellow, thoracic and abdominal tergites white. Head. Frontal suture distinctly U­shaped, terminating in a broad opening ( Fig. 1 ). Frons with paired, long primary frontal setae, paired, long exterior setae, and paired, long anterior angle setae. Clypeus trapezoidal; dorsolateral region of clypeus with several small setae and three long setae on each side; preclypeus and postclypeus lacking setae. Labrum with anterior angles rounded; anterior margin crenulate, setose, surface with posterior­medial pair of long setae; posterior margin with scattered, short setae. Antennae ( Fig. 2 ) 4­segmented; 1st segment short, cylindrical, 1/6 length of 2nd segment; 2nd segment long, clavate; 3rd segment clavate, widening distally, apical surface broadly rounded, bearing large sensory spot; 4th segment narrow, apex with two short setae, and a single long seta laterally. Epipharynx ( Fig. 3 ) broadly rounded, anterior margin lined with long, broad setae. Chaetoparia with four distinct, large setae. Phoba with oval pattern of small setae. Pedium with small patch of granules on dexiophoba side. Protophoba with three blunt, short setae. Epipharynx with united tormae and three nesia: right nesium ovate, median nesium elongate, wider at posterior end, slightly tapering toward anterior end, left nesium small, tear shaped. Mandibles black along margins, well sclerotized, 0.9 mm long. Left mandible ( Fig. 4A ) in dorsal view with blunt scissoral area, slightly bilobed in appearance; ventral process in lateral view prominent under molar area. Right mandible ( Fig. 4B ) in dorsal view with scissorial area blunt, weakly bilobed, angled aborally; ventral process in lateral view prominent below molar area. Maxilla ( Fig. 5 ) with galea and lacinia separated; galea thin, tapering to a blunt apex, medially with a pair of setae; lacinia with sclerotized apex, adoral lateral margin lined with nine pairs of setae; maxillary palpus 4­ segmented: 1st segment globular, aboral lateral margin with a single seta; 2nd segment ovate, subequal to 3rd; 3rd segment ovate, ringed distally with four setae; 4th segment ovate, subequal to 2nd and 3rd segments combined, distally with a sensory patch. Labium ( Fig. 6 ) quadrate, edges slightly sinuate, bearing four distinct, small setae (two medially, two posteriomedially); two V­shaped patches of large setae on anterior margin; labial palpus 2­segmented (appearing almost 3­segmented), last oval, 2× length of first, apically with several circular sensory pits. Thorax. Tarsungulus of prothoracic leg ( Fig. 7 ) with single claw, large setae adjacent to apex; short, blunt, broad seta medially on claw. Mesothoracic leg ( Fig. 8 ) with stridulatory area of coxa long, ovate; stridulatory area with vertical line of small, short setae, and grainy surface. Inner metathoracic leg ( Fig. 9 ) with oval stridulatory area on trochanter, stridulatory area with 14 ridges. Abdomen. Abdomen consisting of 10, non­plicate segments. Spiracles ( Fig. 10 ) cribriform, oriented cephalad. Last (=10th) abdominal segment with anal opening Y­ shaped ( Fig. 11 ), bearing two large, ovate lower anal pads caudally, slightly grainy in texture; upper anal pad broadly triangular, conforming with Y­shape; entire caudal region surrounded by circle of large setae.

Generic Placement Nicagus larvae possess all of the traditional synapomorphic characters of Lucanidae . Previous placement in Trogidae ( Kikuta 1986 ) was based solely on characters of the adults. Tabana and Okuda (1992) placed N. japonicus in Lucanidae based on five characters of the adults and three characters of the larvae (antennae 4­segmented, abdominal segments without folds, and mesothoracic and metathoracic legs each with a stridulatory organ). They suggested that Nicagus belonged to the lucanid subfamily Aesalinae ( sensu Holloway 1968 ) based on similarities of larvae to Aesalus Fabricius and Ceruchus MacLeay in three additional characters: apex of abdomen with three anal lobes, 2nd antennal segment without setae, and left mandible lacking teeth between the 2–3 apical teeth and molar area. Aesalinae ( sensu Tabana and Okuda 1992 ) was based on the inclusion of Ceruchus . Howden and Lawrence (1974) defined the New World Aesalinae , placing Ceruchus in Syndesinae, and Nicagus in the newly formed Nicaginae . Larvae of N. obscurus demonstrate several character states which contradict placement within Syndesinae ( sensu Howden and Lawrence 1974 ): cephalad spiracle orientation, trochanter of metathoracic leg with single longitudinal row of very short transverse ridges, and the appearance of the three anal lobes, as seen in Lucaninae ( sensu Howden and Lawrence 1974 ). The lack of teeth on the inner margin of the mandible, reduction of the mesothoracic and metathoracic tarsungulus, and the lack of setal patches on the raster are suggestive of Syndesinae. The number of setae present on the claw resembles what is seen in Syndesinae as well as some species of Lucaninae. The three distinct tubercles on the protophoba are also seen in Ceruchus ; however, there are apparent differences. In view of the conflicting larval characters, and in lieu of any other synapomorphic characters to suggest other relationships among the Lucanidae, it appears that continued placement of Nicagus in Nicaginae is the solution for the time being.