Microterys chalcostomus (Dalman)

Guerrieri, Emilio, Formisano, Giorgio & Noyes, John S., 2020, Redescription of Microterys chalcosotmus (Dalman) (Hymenoptera: Chalcidoidea: Encyrtidae), a parasitoid associated with Phenacoccus aceris (Signoret) (Hemiptera: Pseudococcidae) and Kermes spp. (Hemiptera: Kermesidae), with comments on its host relationship, Journal of Natural History 54 (19 - 20), pp. 1213-1222 : 1216-1220

Microterys chalcostomus (Dalman)

( Figures 1 , 2 )

Encyrtus chalcostomus Dalman, 1820: 342 . Lectotype ♀ (designated Graham 1969: 260), Sweden, SNHM.

Encyrtus signatus Nees, 1834: 208 . Type material, Sweden, lost (as subspecies of Encyrtus chalcostomus Dalman ) .

Microterys chalcostomus (Dalman) ; Thomson, 1876: 159.

Description

Female. Length, including ovipositor, 1.9–2.9 mm.

Head ( Figure 1 (a,c)) largely orange, with occiput mostly dark brown but bordered with pale orange dorsally, area behind posterior ocelli dark brown with metallic dark green reflections, dorsal part of interantennal prominence brown with slight coppery and metallic dark green reflections, scrobes paler orange than rest of head, mouth margin dark brown with a weak metallic dark green sheen nearly to level of toruli, gena and temple varying from mostly pale orange to dark brown with a weak metallic green sheen, extreme dorsal part of temple pale orange; antenna ( Figure 2 (a)) with scape entirely dark brown or with dorsal margin dusky orange, pedicel F1, F2 and clava dark brown, F3–F6 varying from entirely pale orange to F3 brown, F4 largely brown mixed with pale orange, and only F5 and F6 completely pale orange; thorax ( Figure 1 (a,c)) dark metallic green with some weak coppery reflections, pronotum with posterior margin and side translucent pale orange, side of mesoscutum narrowly translucent dusky pale orange; tegula proximally pale orange with apex translucent dark brown with a weak brassy and coppery sheen; prepectus pale orange; mesopleuron mostly dark brown with a weak coppery and brassy sheen but small anterior area pale orange; fore wing (Fig. 6) infuscate with area basal to linea calva and a transverse band past venation hyaline, the band narrowly constricted in the middle, basal hyaline area with a small, faint, very inconspicuous, infuscate area below parastigma, venation with submarginal vein and base of stigmal vein pale orange, remainder dark brown; coxae dark brown, apex of fore coxa pale orange; fore femur largely dusky pale orange mixed with dark brown proximally and ventrally, tibia pale orange with dorsal and ventral margins dark brown in proximal two-thirds, tarsus pale orange with apical tarsomere dark brown; mid femur dusky pale orange, tibia dusky pale orange mixed with dark brown in proximal half, spur and tarsus pale orange with apical tarsomere dark brown; hind femur and tibia dark brown, extreme apex of tibia pale orange, tarsus pale orange with apical tarsomere dark brown; propodeum dark brown, side with a distinct metallic blue-green sheen; gaster black, dorsally with a distinct coppery sheen, basal tergite, sides and venter also with metallic dark green reflections; visible part of gonostylus dusky pale orange with a weak brassy sheen and some coppery reflections.

Head about 4.5–5.0× as wide as frontovertex, with smaller specimens generally having a relatively wider frontovertex; eye clothed in setae hardly longer than diameter of facet; frontovertex with fine, very regular, polygonally reticulate sculpture of cell size hardly more than half diameter of eye facet, slightly granular in appearance; ocelli forming an angle of about 50°; antenna ( Figure 2 (a)) with scape varying from 3.1× to 3.5× as long as broad, F1 varying from 1.5× to 1.9× as long as broad and about 0.7× as long as pedicel; apex of clava slightly obliquely truncate; mandible tridentate, palp formula 4–3. Relative measurements: HW 173, FV 37, POL 17, OOL 1.5, OCL 13, SL 86, SW 24.5.

Mesoscutum with sculpture similar to frontovertex but slightly shallower and smoother; scutellum with very slightly coarser and more irregular sculpture than that on mesoscutum; fore wing ( Figure 2 (b)) about 2.5× as long as broad, venation as in Figure 2 (b). Relative measurements: FWL 212, FWW 86; HWL 156, HWW 51.

Gaster with ovipositor hardly exserted, the exserted part about 0.25× as long as mid tibial spur; ovipositor ( Figure 2 (d)) about 1.3× as long as mid tibia and 4.6× as long as gonostyli; hypopygium as in Figure 2 (c). Relative measurements: OL 84.5, MT 66.5, GL 18.5.

Male. Length 1.3–2.2 mm.

Head and dorsum of thorax ( Figure 1 (d)) generally bright metallic green with some coppery reflections; antenna with scape pale yellow, pedicel pale orange, dorsally dark brown, flagellum pale orange; tegula pale yellow, apex translucent pale grey-brown; prepectus translucent very pale yellow; mesopleuron dark brown with a weak coppery and brassy sheen, below tegula pale yellow; wings completely hyaline, venation brown; fore and mid coxae pale orange, mid coxa brown at extreme base ventrally, hind coxa dark brown, extreme apex pale orange; legs mostly very pale orange but apical tarsomere on each leg brown, hind tibia with a pair of broad brown rings, upper ring paler and less distinct; metanotum dark brown with a coppery sheen; metapleuron with a metallic green sheen, border with propodeum coppery; propodeum dark brown with a coppery sheen, side largely with a strong metallic green sheen, border with metapleuron coppery; gaster black, dorsally with a distinct coppery sheen, basal tergite, sides and venter also with metallic dark green reflections.

Head about 2.5× as wide as frontovertex; eye clothed in setae hardly longer than diameter of facet; frontovertex with slightly irregular, polygonally reticulate sculpture of cell size hardly less than diameter of eye facet, slightly coarse in appearance; ocelli forming an angle of about 80°; antenna ( Figure 2 (f)) with scape 1.9× as long as broad, F1 about 3.5× as long as broad and about 3.3–3.6× as long as pedicel, smaller specimens having a relatively shorter F1; flagellum clothed in dense short setae, dorsal setae apically slightly curved, ventral setae straight, the longest about 0.8× as long as diameter of segment.

Mesoscutum and scutellum with sculpture similar to frontovertex but very slightly shallower; fore wing ( Figure 2 (e)) about 2.2× as long as broad, venation as in Figure 2 (e).

Gaster with aedeagus ( Figure 2 (g)) about 0.5× as long as mid tibia.

Hosts. Reared from adult females of Phenacoccus aceris ( Hemiptera : Pseudococcidae ) on Sorbus aucuparia , Tilia sp. , Malus sp. and Ulex sp. The males are solitary or gregarious with up to 3 males emerging from a single host; the females are almost always solitary. Recorded from the same host by Ferrière (1955), Schmutterer (1955) and Sentenac and Kuntzmann (2003). The record of Phenacoccus piceae (Löw) as a host ( Noyes and Hayat 1994) is erroneous as it is based on the above record from Ferrière (1955). Also recorded as an egg predator of Kermes quercus Linnaeus , K. roboris Fourcroy and K. corticalis Nassonov (see Trjapitzin 1989).

Distribution. Recorded here for the first time from the Isle of Man, but previously recorded from many European countries, from Sweden, the United Kingdom and Spain to Ukraine and the Transcaucasus (see Trjapitzin 1989; Noyes 2019).

Material examined

ISLE OF MAN, 8 ♀, 12 ♂, Douglas , ex Phenacoccus aceris on Tilia sp ., collected May 1999, June 1999 and June 2000, (F.D. Bennett); 1 ♀, 3 ♂, Douglas , ex Phenacoccus aceris on Malus sp ., collected June 1999 and May 2002 (F.D. Bennett); 1 ♀, Laxey, Glen Gdn, as adult on leaf of beech, 3 September 1999 (F.D. Bennett); 9 ♀, 12 ♂ Ѓ, Douglas, ex Phenacoccus aceris on rowan, collected June 2000 and June 2002 (F.D. Bennett) [2 ♀, 2 ♂, used for DNA extraction, reference EG MIC002, EG MIC003, EG MIC004, EG MIC006 respectively]; 42 ♀ 50 ♂, Laxey , Baldhoon Road, Crofton, SC 4284, as mummified mealybug Phenacoccus aceris on gorse, various dates in June 2015, July 2016 and May 2017 (F.D. Bennett) . Material in NHMUK and DEZA.

The adults emerged from the mummified mealybugs about 2–4 weeks after collection.

Comments. Among the known species of Microterys recorded as parasitoids of mealybugs, M. chalcostomus appears to be most similar to M. subcupratus ( Dalman, 1820) , the only other Palaearctic species known to parasitise this group of hosts where the female has the scape 3–4× as long as broad and a single hyaline band on the fore wing. The two can be readily separated by the colour of the head and F4. In M. chalcostomus the head is largely orange and F4 is pale orange, whilst in M. subcupratus the head is completely black with violet and metallic green reflections and F4 is dark brown. The colour of female antennae seems to be reliable for separating the species of this genus. In northern Europe, females of M. chalcostomus are also somewhat similar to those of M. cyanocephalus (Dalman) , but differ in having the frontovertex, F5 and F6 pale orange, whereas in M. cyanocephalus the head is dark brown and only F6 is pale orange.

Figures

Figure 1. Microterys chalcostomus: (a) lectotype ♀(habitus); (b) labels accompanying lectotype; (c) habitus, ♀; (d) habitus ♂. (Courtesy of Hege Vårdal.)

Figure 2. Microterys chalcostomus: (a) antenna ♀; (b) fore wing ♀; (c) hypopygium ♀; (d) ovipositor; (e) fore wing ♂; (f) antenna ♂; (g) genitalia, ♂. (Images from slides, all bright field illumination except Fig. 1(g) differential interference contrast).