Homalictus achrostus Michener, 1979

Dorey, James B., Schwarz, Michael P. & Stevens, Mark I., 2019, Review of the bee genus Homalictus Cockerell (Hymenoptera: Halictidae) from Fiji with description of nine new species, Zootaxa 4674 (1), pp. 1-46 : 8-10

Homalictus achrostus Michener, 1979

( Figs 4–5 )

Material examined. Type material ♂: Fiji, Viti Levu Nandaravatu, 1,100 m Microwave Stn. 16–23.VIII.78 S.&J. Peck-Mal. Trap. Holotype Homalictus achrostus C.D. Michener. Holotype Homalictus achrostus Michener CNC No. 15918.

Allotype ♀, and 4 ♀ paratypes: FIJI: Viti Levu : malaise trap at telecom tower, Nadarivatu, 1,100 m altitude, 1–16.VIII.1978, S & J Peck (after Michener 1979) . Holotype and allotype in SEMC, paratypes deposited in CNC, BPBM and NHMUK. The material below is consistent with the type specimen described by Michener (1979) .

Other material examined. 1 ♂: AFO055, 1/9/10, 10:03 AM, 1,040 m asl, -17.5762, 177.9350, SVC Groom , Viti Levu . 1 ♀: AFO056, 1/9/10, 10:03 AM, 1,040 m asl, -17.5762, 177.9350, SVC Groom , Viti Levu .

Diagnosis. Males: Bee mostly black. Additionally, males of H. achrostus also have comparatively large mandibles ( Fig. 4d ), a strong medial depression of their clypeus ( Fig. 4d ), strong striations on the dorsal surface of their propodeum ( Fig. 4a ) and comparatively elongate gonostylus ( Fig. 4e ).

Females:Bee mostly black. Additionally, females of H. achrostus have a weaker medial depression of their clypeus ( Fig. 4i ), strong striations on the dorsal surface of their propodeum ( Fig. 3f ) and a longitudinal medial carina on the pygidial plate ( Fig. 4j ).

Description. Males: Measurements: UID 0.95 mm. LID 0.91 mm. AOD 0.31 mm. IAD 0.19 mm. OAD 0.37 mm. IOD 0.24 mm. OOD 0.32 mm. GW 0.36 mm. EW 0.33 mm. BL 5.61 mm. ML 0.14 mm. SL 0.3 mm. FL 4.51 mm.

Colouration: Body (including clypeus, supraclypeal area, frons, paraocular area, scutum, scutellum, propodeum dorsally and metasoma) black. Fovea along anterior and proximal margin of eye present.

Sculpturing: Paraocular area fine striae and colliculate along margin of compound eyes. Frons mostly longitudinal striae and transverse striae under ocelli. Supraclypeal area mostly finely colliculate. Clypeus finely colliculate. Vertex punctures small and sparse. Scutum anteriorly finely colliculate and lineolate; medially moderately fine colliculate and almost smooth; posteriorly finely colliculate and almost smooth. Scutellum almost entirely smooth except for punctation. Scutellum punctation open and sparse. Propodeum; dorsal striae close and strong and weak medial anterior groove present; laterally finely colliculate, some striae anteriorly and dorsally and ventrally; posteriorly finely colliculate and diagonal striae ventrally and proximally.

Morphology: Scape extends to posterior margin of medial ocellus. Interantennal distance greater than diameter of socket. Clypeus strongly depressed medially. Posterior margin of scutum shape mostly straight. Gonostylus elongate, gonocoxite with dorsoapical crest weak ( Michener 1979).

Females: Measurements: UID 0.82 mm. LID 0.83 mm. AOD 0.25 mm. IAD 0.15 mm. OAD 0.43 mm. IOD 0.19 mm. OOD 0.26 mm. GW 0.27 mm. EW 0.35 mm. BL 5.56 mm. ML 0.18 mm. SL 0.34 mm. FL 4.75 mm.

Colouration: Body (including frons, propodeum dorsally, metasoma) black except clypeus, supracylpeal areas, paraocular area, scutum and scutellum black or partially sub-metallic.

Sculpturing: Paraocular area fine striae and colliculate along margin of compound eyes. Frons mostly longitudinal striae and colliculate above antennal sockets. Supraclypeal area mostly finely colliculate. Clypeus finely colliculate. Vertex punctures small and sparse. Scutum anteriorly moderately fine colliculate and lineolate; medially and posteriorly moderately fine colliculate. Scutellum punctation open and sparse. Propodeum; dorsally strong striae close and weak medial anterior groove; laterally finely colliculate and posteroventral and anterior striae curve towards each other and can meet; posteriorly finely colliculate and transverse striae ventrally and proximally.

Morphology: Scape extends to or below anterior margin of medial ocellus. Interantennal distance greater than diameter of socket. Labrum simple. Clypeus moderately depressed medially. Area posterior of vertex with strong and close striae. Posterior margin of scutum shape mostly straight.

Comments. This species was last collected in 2010, where a single male and female were sampled from their type locality near Nadarivatu. When the species was described by Michener (1979) only one male and five females where collected at 1,100 m asl; the highest elevation in the Nadarivatu region. That no more specimens have been collected since 2010, despite intensive searching most years between 2010 and 2018, suggests that this species might have become extinct, perhaps due to the combination of its limited range on a single high mountain peak and global climate warming.

Distribution. Homalictus achrostus has only ever been sampled from the telecom towers at Nadarivatu on the largest island, Viti Levu ( Michener 1979), with only two specimens sampled in this study, both in 2010 ( Fig. 5 ). Our specimens of H. achrostus were sampled at 1,040 m asl.

Figures

FIGURE 3. (a) maximum credibility tree of the Fijian Homalictus where branch colour represents (b) geographic location. Numbers show posterior probability at nodes.

FIGURE 4. Homalictus achrostus male (a) dorsal habitus, (b) lateral habitus, (c) dorso posterior, (d) anteriorly frontal face and (e) ventral genitalia. Female (f) dorsal habitus, (g) lateral habitus, (h) dorso posterior, (i) anteriorly frontal face and (j) pygidial plate.

FIGURE 5. Collection map of Homalictus achrostus from specimens with identity confirmed by mtDNA COI gene. Sample size is 2.