Australambrysus plax (La Rivers) Sites, 2023

Sites, Robert W., 2023, The Australambrysus plax (La Rivers, 1967) species complex (Heteroptera: Naucoridae), with descriptions of three new species, Zootaxa 5278 (2), pp. 318-332 : 320-323

Australambrysus plax (La Rivers) NEW STATUS

( Figs. 3b , 4d–f , 5 , 9 )

Ambrysus planus plax La Rivers 1967 : Biol. Soc. Nev. Occas. Pap. 14: 1–3.

Australambrysus planus plax: Reynoso-Velasco & Sites 2021 , Syst. Entomol. 46: 907.

Discussion. Australambrysus planus ( La Rivers, 1951) was described from several specimens collected in Peru in 1935. A subspecies, A. planus plax ( La Rivers, 1967) , was described from a single male specimen collected in Costa Rica in 1939. No further mention of either subspecies has appeared in the literature other than their inclusion in a catalog of the Naucoridae ( La Rivers 1971) and in the molecular phylogenies of Reynoso-Velasco & Sites (2021) and Sites (2022). Each subspecies is known as a different wing morph, although very few specimens are known; A. p. planus is macropterous whereas A. planus plax is brachypterous. These two subspecies share a feature that the three new species described here lack: the posterolateral corner of abdominal segment III is produced to an acute point ( Fig. 4d inset), whereas the corner is distinctly right-angled in the three new species.

Three differences were given to distinguish the subspecies from each other ( La Rivers 1967). Overall body size of A. planus plax differs from A. p. planus in being smaller (8 mm length), with the nominate subspecies 9.0– 10.25 ( La Rivers 1951); the hemelytra are short and the claval sutures are suppressed ( Figs. 3b , 4d ); and the short posterolateral pronotal margin between the lateral and posterior margins is straight rather than shallowly concave and the angles are blunt rather than sharp (compare Fig. 3a and 3b ) ( La Rivers 1967). The taxonomic reliability of these features is questionable because wing morph can have a bearing on prothoracic shape and claval development. In addition, body size can vary intraspecifically with ontogenetic development in different thermal environments ( Sites et al. 1996).

Presented here are new records of a male A. p. planus from Ecuador and a male A. planus plax from Colombia. Based on comparison with the types and La Rivers’ descriptions, they match the respective holotypes well. In addition to the body size, hemelytra development, and pronotum shape differences given by La Rivers (1967), dissections of these new specimens revealed the parameres ( Fig. 4c, f ) and abdominal tergum VIII ( Fig. 4b, e ) to be dramatically different between the subspecies. The specimen of A. p. planus had been dissected previously and only the left paramere was available for examination. Thus, although it is clearly distinct from that of A. planus plax , determination of symmetry cannot be made. Abdominal tergum VIII medial lobes are wider than long in A. planus plax and longer than wide in A. p. planus ; the lateral and mesal margins of each lateral lobe are mostly parallel in A. planus plax , but widen and become angulate laterally in the distal third in A. p. planus . Further, A. planus plax has shallowly convex lateral margins of the pronotum rather than straight lateral margins as in A. p. planus .

Australambrysus planus plax is morphologically more allied to the three new species described here than it is to A. p. planus . Thus, elevation of A. planus plax to species level recognition is proposed. I consider A. acutangulus , A. planus , A. siolii , and A. teutonius to be members of the A. plax species complex based on similar propleural conditions with respect to the prosternum.

Diagnostic features. In addition to the propleuron being appressed to the probasisternum and prosternellum, Australambrysus plax has shallowly convex, convergent lateral margins of the pronotum and well-developed posterolateral abdominal spines beginning on segment III ( Figs. 3b , 4d ). The lateral lobes of abdominal tergum VIII are nearly parallel throughout their lengths to the broadly rounded apices, and the medial lobes (= pseudoparameres) are wider than long ( Fig. 4e ). The parameres are symmetrical ( Fig. 4f ).

Habitat description. I have collected at the type locality of A. plax ( Fig. 5a ), which is also the type locality of Cryphocricos latus Usinger, 1947 ( Naucoridae : Cryphocricinae ). The marginal vegetation habitat characteristic of other species in the A. plax species complex was present, although I did not find A. plax . In Quebrada Cañaveral in Colombia, I collected a male specimen from marginal vegetation ( Fig. 5b ).

Distribution. Australambrysus plax is known from only the holotype ( Costa Rica). Here, I add a record of A. plax from Colombia. In addition, A. planus has been reported from only Peru and I here add a record from Ecuador.

Type material examined. HOLOTYPE ♁ Australambrysus plax : COSTA RICA, C.A. San Isidro del. Gen., 2000 ft. Feb. 1939, Dean L. Rounds / Ambrysus planus plax ♁ Holotype / Ira La Rivers collection bequeathed to the California Academy of Sciences - 1978 / California Academy of Sciences Type No. 13410 ( CAS). HOLOTYPE ♁ Australambrysus planus : PERU, Vic. Sani Beni, 840 m. a.s.l., River S. Beni and adj. pools / Peru, S.A., Aug. 5 1935, F. Woytkowski, Field No. 3553d / Ambrysus planus La Rivers Holotype ( SEMC).

Additional material examined. Australambrysus plax : COLOMBIA: Dpto. Antioquia, Mpio. San Carlos, Qda. Cañaveral , 0612.185’N, 7456.738W, 929 m, 27 March 2016, L-1946, R.W. Sites & P. Gómez colls., DNAextraction #H5 (1♁ UMC) . Australambrysus planus : ECUADOR: Morona-Santiago, Gualaquiza (17 km SW) , 0338’S, 7834’W, 20 Sep 1990, P.J. Spangler & K. Bastidas, colln #29 (1♁ UMC) .

Figures

FIGURE 3. Dorsal habitus of holotypes of a) Australambrysus planus (La Rivers) and b) A. plax (La Rivers). Size bar = 2.0 mm.

FIGURE 4. a–c) Australambrysusplanus from Ecuador.a)Dorsal habitus, b) tergum VIII,c) leftparamere.d–f) Australambrysus plax from Colombia. d) Dorsal habitus with lateral margin of tergum III in inset, e) tergum VIII, f) parameres. ll = lateral lobe, ml = medial lobe. Sizes are not proportionate among figures.

FIGURE 5. Collectinglocalities of Australambrysus plax. a)Type locality of Río San Isidro, Costa Rica, b) Quebrada Cañaveral, Colombia.

FIGURE 9. Distribution records of species in the Australambrysus plax species complex.