Micromyzus platycerii sp. n. (Hemiptera, Aphididae) – a new fern-feeding aphid species from Thailand

Abstract A new fern-feeding aphid species, Micromyzus platycerii, collected in Sakaerat Research Station in Thailand, is described.


Introduction
There are approximately 66 species of fern-feeding aphids worldwide, belonging to 18 genera (Blackman and Eastop 2006). A few of them are polyphagous species more commonly found on angiosperms, but most of them are specialized on ferns. Most of these specialized genera occur in tropical and subtropical regions and their geographical ranges overlap considerably.
Among them are two very similar and probably related fern-feeding aphid genera: Micromyzella Eastop and Micromyzus van der Goot. Micromyzella comprises around 12 species, inhabiting mainly south-east Africa but also the Philippines and Indonesia (Remaudière and Autrique 1985). Its main morphological characteristics are 2-3 setae on first tarsal segments (including 1 sensory, peg-like seta) and, in alate females, darkly colored wing veins with the radial sector moderately curved (Blackman and Eastop 2006). Micromyzus is similar, but usually with 4 setae on the first tarsal segments (including 2 sensory peg-like setae) and, in alate females, heavily bordered wing veins and a strongly curved radial sector. It comprises about 10 species, distributed mainly in south-east Asia.
The Sakaerat Environmental Research Station (SERS) is situated on the edge of Thailand's Khorat Plateau approximately 300 km north-east of Bangkok (SERS 2014). It was created in 1977, as a site for research on dry evergreen and dry dipterocarp tropical forest (Trisurat 2010). Other vegetation types in the biosphere reserve include bamboo forests, forest plantations and grasslands. During the field studies in SERS in January 2014, samples of fern-feeding aphids were collected. Here we describe a new species of fern-feeding aphid belonging to the genus Micromyzus, collected recently in Sakaerat Environmental Research Station. All slides are deposited in the collection of the Department of Zoology, University of Silesia (UŚ).

Material and methods
Measurements and diagnostic, morphological features follow Takahashi 1925, Miyazaki 1968, Noordam 2004and Blackman and Eastop 2006. -higher number of accessory hairs on ultimate rostral segment than in M. pojanii; -lower number of secondary rhinaria on antennal segment III than in M. hangzhouensis.
Prothorax sclerotised, mesothorax with marginal and spinal sclerites, metathorax with marginal sclerites only. Mesothoracic furca not separated, weakly pigmented. Legs covered by short, pointed hairs, shorter than the middle diameter of tibia. Distal half of femora dark; tibiae pale except for dark apices, tarsi black. Ventral side of each first tarsal segment with one thick, pointed, peg-like seta and two thinner setae (Fig. 3). Second segment of tarsus 0.096-0.103 mm long.
Abdomen membranous, with single, very small marginal scleroites, sometimes bearing a small marginal tubercle on abdominal tergite II or III. Small antesiphuncular and bigger postsiphuncular sclerites present. Each tergite with a row of short, pointed setae. Reniform spiracles placed at the posterior end of small scleroits. Siphunculi dark, slightly swollen in the middle, discretely imbricated, with 2-3 rows of distinct imbrications just below the apex (Fig. 4), 0.59-0.69 mm long, 2.57-2.77 of cauda. Subgenital plate broadly elliptical, 0.26-0.31 mm wide, with 2-3 longer setae on its anterior border and a row of shorter setae at its posterior border. Cauda pale, fingershaped with broader base, 0.22-0.27 mm long, with 4-5 setae (Fig. 4).
Thorax heavily sclerotised. Wings with very dark pigmentation of veins and their borders, especially on proximal cubital vein (Fig. 2). Media of fore wing with two forks. Radial sector strongly curved. Legs dusky, with darker apices of femora and tibiae, covered with short pointed setae. Tarsi dusky, first segment with 3 setae, including one sensory peg-like seta; second segment of hind tarsus 0.09 mm long.
Abdomen membranous, with transverse rows of short, pointed setae and with marginal sclerites only. Antesiphuncular and postsiphuncular sclerites well developed. Reniform spiracles placed at the posterior end of small scleroits. Genital plate broadly oval, 0.23-0.26 mm wide, with two setae on the anterior edge and 4-6 setae on the posterior edge. Siphunculi 0.50-0.51 mm long, 2.60-3.08 of the length of cauda, clavate, slightly swollen in the middle, dusky, with 2-3 rows of distinct imbrications at the apex, just below weakly developed flange (Fig. 8). Cauda finger-shaped, pale, 0.17-0.19 mm long, with 4-5 setae.
Biology. The brown, shiny aphids were feeding on young shoots of Platycerium coronarium, in great numbers on the undersides of leaves.

Taxonomic comments
Micromyzus platycerii sp. n. has 3 hairs on first tarsal segments, including one peg-like, sensory seta, which is a characteristic of the genus Micromyzella Eastop. The key presented by Su et al. (2014) leads to undeterminable point 9, with morphological features of apterae similar to Micromyzella, but of alatae similar to Micromyzus. However, species in the genus Micromyzus, including M. katoi, also have 3 setae on first tarsal segments (Noordam 2004, Miyazaki 1968). The generic classification of the collected specimens was primarily based on the morphology of wing, which in its pigmentation and strongly curved radial sector undoubtedly puts it into the genus Micromyzus (Blackman and Eastop 2006). (In a key to alate morphs by Noordam (2004) it is stated that the forewings of M. katoi are not bordered with black, but this is evidently a typographic error, and the forewing is correctly illustrated in the same work).
Viviparous females of Micromyzus platycerii sp n. are morphologically very similar to M. katoi. Both species have a membranous abdomen, dark siphunculi, clavate in shape and with a few rows of imbrications, pale cauda with 4-5 setae and darker tips of antennal segments (Takahashi 1925). They most resemble the Australian "Micromyzus ? katoi" of Eastop (1966), the only discriminant character being the ratio of length to middle diameter of siphunculi, which seems to be higher in the new species. From the illustration in Eastop's work, this ratio is lower (c. 5.75) in the alate morph of the Australian M. katoi than in alate of the new species (7.04-8.86). Furthermore, according to Blackman and Eastop's (2006) key, apterae of M. katoi (including Eastop's M. katoi) have a siphunculus/cauda ratio of 2.4 or less, whereas in apterae of the new species it is well above this value.
The observed differences, including the variable chaetotaxy of the first tarsal segments, put in question taxonomic relations within the Micromyzus/Micromyzella group and indicate a strong need for revision of the fern-feeding aphids of the tropical and subtropical region.