Parastethynium maxwelli ( Girault, 1915 )

Huber, John T., Gitau, Catherine W., Gurr, Geoff M., Dewhurst, Charles F. & Fletcher, Murray J., 2011, Re-description and biology of Parastethynium maxwelli (Hymenoptera: Mymaridae), an egg parasitoid of Zophiuma lobulata (Hemiptera: Lophopidae), and description of a new species of Parastethynium from Indonesia, Zootaxa 2733, pp. 49-62 : 52-60

Parastethynium maxwelli ( Girault, 1915)

( Figs 1–15 , 19–50 )

Stethynium maxwelli Girault 1915: 162 ; Dahms 1984: 801 (types).

Parastethynium maxwelli (Girault) : Lin et al. 2007: 56 + figs 280–284 (redescription of female, incorrectly retained in Stethynium ).

Type material. Holotype female ( Figs 1–5 ), in poor condition under a piece of broken cover slip on a slide broken into several pieces and stuck together with tape ( Fig. 5 ). It is together with the holotype of Stethynium gladius Girault (under a separate, broken piece of cover slip).

Diagnosis. Forewing with microtrichia posterior to venation relatively sparse, with a larger asetose lenticular area anterior to retinaculum bordered anteriorly with one row of microtrichia ( Figs 1 , 15 ); scutellum with placoid sensilla well separated from each other and from anterior margin ( Figs 1 , 8, 9 ). The very similar species, P. hirsutum Huber , described above, has the scutellum with the placoid sensilla almost touching each other and the anterior margin of the scutellum ( Fig. 17 ), the fore wing microtrichia posterior to venation almost as dense as more distally, i.e., with smaller asetose areas, two rows of microtrichia bordering the asetose lenticular area anterior to the retinaculum, and the hind wing width at the level of the hamuli less than half the maximum wing width ( Fig. 16 ).

Description. FEMALE. Body length 870–1000 µm (n=15). Body colour dark brown except frenum light yellow to almost white, humeral plate and area immediately under wing insertions white with brown tinge, and apical tergite and cercal plate lighter brown than preceding tergites ( Figs 6–8 , cleared, slide mount). Scape and pedicel brown, flagellum yellow. Mouthparts except mandibles white, mandibles brown except teeth with reddish tips. Coxae except brown bases, and trochanters white, remainder of legs yellow except apical tarsomere of middle and hind legs and pretarsus of all legs brown. Body and appendage setae mostly white, their sockets brown.

Head. Head width 267–293 (n=5). Face and vertex ( Figs 19, 20 ) with engraved, isodiametric reticulate sculpture, gena and occiput ( Fig. 20 ) along posterior orbit with elongate reticulate sculpture. Eye dorsally usually extending to back of head (e.g., Figs 6, 7 , 21, 22 ), usually collapsed, even in non-teneral specimens killed in ethanol. Mouth opening laterally with separate, narrow sclerite between base of mandible and gena ( Fig. 23 ). Mouthparts ( Figs 23, 24 ) with the mandibles with the distinct ventral tooth separated from the wide dorsal tooth consisting of an uneven serrated edge with 2 smaller between 2 larger teeth.

Antenna. Scape with faint, longitudinal striations, with inner, dorsal, and ventral surfaces densely setose and outer surface without setae ( Figs 21 , 26, 28). Funicle and clava (Figs 25, 27) densely setose, the setae about as long as a segment width. Fl3 and fl5 each with 2 longitudinal sensilla, the remaining funicle segments without longitudinal sensilla (fl1, fl2, fl4, and fl6 incorrectly stated as each having 1 longitudinal sensillum in Lin et al. 2007); claval segments each with 2 longitudinal sensilla. Measurements length/width (n=3, except scape): scape 106/35, pedicel 57–60/33–36, fl1 45–50/20–22, fl2 47–50/20–23, fl3 47–54/22–23, fl4 38–46/20–23, fl5 47–51/22–23, fl6 37–40/22– 24, clava (total) 95–108/33–36.

Mesosoma. Sculpture engraved reticulate, more or less isodiametric on mesoscutal midlobe anteriorly, lateral lobe, axilla medially, and scutellum, more or less elongate on pronotum, propleuron, mesoscutal midlobe posteriorly, axilla laterally, and frenum (Figs 29–31). Setae mostly erect and fairly long except the anterior two pairs on pronotal lobe. Midlobe of mesoscutum with setae midway between anterior and posterior margins of sclerite. Scutellum with placoid sensilla separated from each other and from anterior margin of scutellum by about 2– 3 X their diameter. Prosternum (Fig. 32) with 5 or 6 pairs of setae; mesosternum (Fig. 32) with 2 pairs of setae posteiorly, bordering the discrimmen.

Wings. Fore wing ( Fig. 15 ) distinctly infumate except for basal cell and a well defined oval hyaline area in apical 0.66 of wing beyond venation. Measurements (n=3): length 849–873, width 302–330, length/width ratio 2.73– 2.88, longest marginal setae 38–50, about 0.12–0.17X as long as greatest wing width. Hind wing ( Fig. 15 ) faintly infumate, slightly more so towards apex and along anterior margin, and relatively wide with rounded apex. Length 777–792, width 93–106, longest marginal setae 60–71, about 0.57–0.58X as long as greatest wing width; width at hamuli about 0.59 greatest width.

Legs. Coxae and femora finely, longitudinally reticulate. Tibiae and tarsi densely setose ( Figs 47, 49, 50 ). Mesotibial spur ( Fig. 49 ) slightly curved, longer than protibial calcar ( Fig. 48 ) and twice as long as the short, straight metatibial spurs ( Fig. 50 ).

Metasoma. Petiole ring-like, with a broad, oblique attachment to propodeum ( Fig. 33 ). Gaster ( Figs 33, 35, 36 ) with extremely thin, mostly smooth cuticle and the overlapping segments closely appressed, thus sometimes almost indistinguishable from one another. Each apparent tergum with 3 or 4 long setae, laterally on gt1–gt4 and sublaterally as well on gt5 and gt6, the latter two segments slightly the longest, both with a group of minute spicules mediodorsally; syntergum (fused gt7–gt8) almost as long as wide anteriorly, conical, with several long setae in 3 transverse rows. Spiracle absent. Cerci flat, with the usual 4 setae. St3–6 each with a row of long setae; outer plate of ovipositor with numerous setae bordering ovipositor sheath ( Fig. 36 ). Ovipositor as long as gaster ( Fig. 35 ), exserted slightly beyond gastral apex ( Figs 34, 36 ).

MALE. Similar to female except as follows. Body length 680–800 µm (n=5). Body colour yellow with slight brown suffusion, except occiput brown dorsally ( Figs 9–11 , cleared, slide mounts). Exceptionally, body darker brown, as in female (one specimen seen). Rarely, light brown, with more or less extensive yellow areas, especially lower face and gena, parts of mesosoma dorsally, propodeum, and apex of metasoma. Flagellum brownish yellow, FIGURES 25–32. Parastethynium maxwelli female, micrographs. 25, antenna lateral inner; 26, scape–fl2,lateral inner; 27, fl2– clava, dorsal; 28, scape and pedicel, dorsal; 29, mesosoma dorsal; 30, frenum–base of gaster; 31, mesosoma lateral; 32, mesosoma ventral.

FIGURES 40–46. Parastethynium maxwelli male, micrographs. 40, antenna lateral inner; 41, fl9 –fl11 lateral, inner; 42, scape–f l1 lateral inner; 43, metasoma dorsal; 44, gaster apex; 45, metasoma lateral; 46, gaster apex lateral.

only slightly darker than scape and pedicel. Legs, including apical tarsomere of fore leg, yellow, pretarsus brown. Mandibles entirely reddish.

The lighter body colour of males ( Fig. 9 ) compared to females ( Fig. 8 ) is remarkable.

Antenna. Flagellar segments densely setose and apical two flagellomeres broadly joined to each other (Figs 40–42). Measurements (length) (n=3): scape 104–107, pedicel 54–56, fl1 45–51, fl2 40–42, fl3 41–45, fl4 38–48, fl5 40–48, fl6 42–47, fl7 41–46, fl8 44–45, fl9 46–48, fl10 42–50, fl11 38–45. Fl6 width 26, 1.7–1.8X as long as wide, with 4 or 5 multiporous plate sensilla.

Head. Gena relatively wider dorsally ( Figs 37, 38 ) than in female but mandibles similar ( Fig. 39 ).

Metasoma. Syntergum (fused gt7–gt8) about half as long as wide anteriorly, more rounded apically, with shorter, more closely spaced setae (Figs 43, 44). The two preapical sternites each with transverse row of erect setae along posterior margin (Figs 45, 46). Apical sternum V-like, incised, bordered medially with about 14 short erect setae on each side of genitalia ( Figs 13, 14 ). Genitalia ( Figs 12–14 , 46) with long digiti, each with a long laterally projecting seta at about its mid-length.

Material examined. Numerous specimens in ethanol, a few of them critical point dried or slide mounted: AUSTRALIA: Queensland, Heathlands ( Lin et al. 2007). INDONESIA: Seram, Solea [12 km W. Wahai], viii.1987, M. Day (2 females, CNC); PAPUA NEW GUINEA: Milne Bay, Milne Bay Estates, Hagita Li, block 1190, 10 º19’36”S 150º17’45”E, coll. 14.iii, em. 16.iii.2010, C.F. Dewhurst (3 females, 5 males, CNC); West New Britain, Dami Oil Palm Research Station, 5º31’53”S 150º20’67”W, 5-8.iii.2010, E. guineensis (numerous males and females in ethanol, BMNH, CNC, UCR, USNM); Unknown province, Awar bush, 7.xii.1982, P. Grootaert (1 female, CNC).

Distribution. Australia, Indonesia, and Papua New Guinea. The known range known so far extends about 14º latitude (2º48’– 16º55’S) and 11º longitude (129º29’– 150º21’E), which is not a particularly large distribution for a species of Mymaridae .

Host. Zophiuma lobulata Ghauri ( Hemiptera : Lophopidae ) on betel-nut palm ( Areca catechu ), coconut palm, and oil palm ( Ghauri 1967; Prior et al. 2001). The host in Australia is unknown.

Biological remarks for Parastethynium maxwelli . Mean development time (egg to adult) was 11 days (range 9–13). Mean number of parasitoids produced per egg mass was 57 (range 29–103) with a mean female proportion of 0.59 (range 0.00–0.72). Parastethynium maxwelli females lived significantly longer on honey and water, compared to water alone, and nil (χ2=11.7; P=0.008) but this did not apply to males (χ2=0.50; P=0.78) ( Fig. 51 ).

Figures

FIGURE 51. Longevity (in days) of P. maxwelli females and males when provided with Honey + Water (35 females, 13 males), Water alone (40 females, 8 males) and Nil (39 females, 9 males). Error bars are standard errors of the means.

FIGURES 1 – 5. S tethynium maxwelli Girault, holotype. 1, body dorsal; 2, head posterior and dorsal; 3, head, anterior and ventral; 4, mandibles; 5, holotype slide.

FIGURES 6 – 14. Parastethynium maxwelli (Girault), cleared, slide mounts. 6, female lateral; 7, female head dorsal; 8, female mesosoma + metasoma dorsal; 9, male body dorsal; 10, male antennae lateral; 11, male metasoma ventral; 12, male gastral apex + genitalia lateral; 13, male gastral apex ventral; 14, male genitalia ventral.

FIGURES 15 – 18. Parastethynium spp., cleared, slide mounts. 15, P. maxwelli, wings; 16, P. hirsutum Huber, holotype, wings; 17, P. hirsutum, holotype mesosoma; 18, holotype slide.

FIGURES 19 – 24. Parastethynium maxwelli female, micrographs. 19, head anterior; 20, head posterior; 21, head dorsal; 22, head laterodorsal; 23, mouthparts anterior; 24, mouthparts, posterior.

FIGURES 33 – 39. Parastethynium maxwelli, micrographs. 33, female gaster dorsal; 34, female gaster apex; 35, female gaster lateral; 36, female gaster ventral; 37, male head lateral; 38, male head ventral; 39, male head, mouthparts.

FIGURES 47 – 50. Parastethynium maxwelli legs posterior, micrographs. 47, fore leg; 48, fore leg calcar; 49, middle leg; 50, hind leg.