Aleiodes pallidator (Thunberg, 1822)

van Achterberg, Cornelis & Shaw, Mark R., 2016, Revision of the western Palaearctic species of Aleiodes Wesmael (Hymenoptera, Braconidae, Rogadinae). Part 1: Introduction, key to species groups, outlying distinctive species, and revisionary notes on some further species, ZooKeys 639, pp. 1-164 : 93-98

Aleiodes pallidator (Thunberg, 1822) Figs 257, 258-259, 260-271

Ichneumon pallidator Thunberg, 1822: 259 .

Aleiodes pallidator ; Shenefelt 1975: 1179; Papp 1991: 101; Belokobylskij et al. 2003: 398.

Rogas pallidator ; Tobias 1986: 81 (transl.: 135).

Rogas ochraceus Curtis, 1834 : 512.4; Shenefelt 1975: 1182 (as synonym of Aleiodes testaceus ) (examined).

Aleiodes ochraceus ; Papp 1991: 101 (as synonym of Aleiodes pallidator ); Belokobylskij et al. 2003: 399 (as synonym of Aleiodes similis ).

Aleiodes unicolor Wesmael, 1838: 111 ; Roman 1912: 271 (synonym of Aleiodes pallidator ); Shenefelt 1975: 1179-1180; Papp 1985a: 160 (lectotype designation) (examined).

Type material.

Lectotype of Ichneumon pallidator here designated, ♀ (ZMUU) from Sweden ( “α”, " Rhogas (Aleiodes) pallidator Thbg "). Holotype of Rhogas ochraceus , ♀ (Melbourne) from England ( Regent’s Park), “Type”, " Rhogas ochraceus Curtis , type, J.F. Perkins, 1948". Lectotype of Aleiodes unicolor , ♀ (KBIN) from Belgium and 2 paralectotypes examined.

Additional material.

British Isles (England: V.C.s 11, 15, 24, 59, 60), Bulgaria, Netherlands (FL: Bant; Lelystad (Jagersbos), FR: Ried, GE: Ede (Maanderbroek); Zaltbommel (Kerkwijk), GR: Scheemda, LI: Reuven; Vlodrop, NB: Nederweert; Geffen; Valkenswaard; Heusden, ZH: Rotterdam; Lexmond; Melissant), Germany, Hungary, *Romania, Russia, Serbia, Slovakia, Sweden, Turkey. Specimens in NMS, BMNH, RMNH, OUM, ZSSM, MCZ, CC, CNC, UWIM, R. van der Hout collection.

Molecular data.

MRS001 (Turkey EU979586, CO1 + EU854333, 28S).

Biology.

A univoltine, thelytokous specialist parasitoid of the erebid lymantriine Leucoma salicis (Linnaeus) , overwintering in the host. More than 200 reared specimens seen from Leucoma salicis (most in NMS, others in BMNH, RMNH, ZSSM, OUM, CC, MCZ). Its biology has been studied by Dowden (1938) in the course of its attempted introduction to North America for the control of the introduced Leucoma salicis : the notes given here supplement rather than repeat his findings. Based on English data the adult flight time is from the last few days of June through to early September. In experimental rearings the females were slow to accept Leucoma salicis larvae, but always did so eventually after repeated contact (being especially attracted to traces of silk), and second instars were only marginally more acceptable than firsts. This may suggest some adaptation to the essentially gregarious nature of early stage Leucoma salicis larvae. Oviposition was brief, usually taking about 5 but sometimes up to 20 seconds: although there was a pre-oviposition sting the female usually did not wait for paralysis to take effect before ovipositing, but would then avoid superparasitism of hosts thus rendered sluggish for a short period, though not subsequently. Partly because of winter mortality exact quantitative data are not available, but from about 100 observed single ovipositions the success rate in Leucoma salicis (partly judged from living established larvae within overwintering hosts) was at least 90%. In one experiment, already briefly reported by Askew & Shaw (1986), a cohort of Leucoma salicis larvae (N = 57) parasitised by Aleiodes pallidator and kept under outdoor conditions came out of their hibernacula a mean of 9.2 days later than controls (N = 66) from the same host egg batch (t = 9.18, P <0.001). This delay was interpreted as extending the range of host plants suitable for the development of parasitised hosts, as spring bud burst varies greatly between the Salicaceae present at the English site of origin (Ainsdale, Lancashire); in addition, however, this behaviour by a monophagous parasitoid might be an adaptation to ensure that there is reasonably good synchrony with the next host generation. In experiments to test host range extension, inexperienced females would not oviposit into other species of Lymantriinae , but females that had already oviposited into Leucoma salicis often would do so quite readily into both Euproctis similis (Fuessly) and Dicallomera fascelina (Linnaeus) , although attempts were often at least for a time thwarted by the longer setae of the trial hosts. In all cases in which oviposition occurred, hosts were later dissected and found to contain encapsulated parasitoids (usually eggs; possibly in some cases first instar larvae). The results of trials were Euproctis similis 2:15\8\\0, Dicallomera fascelina 3:12\6\\0, Orgyia antiqua (Linnaeus) 4:7\0\\-, Lymantria dispar (Linnaeus) 1:5\0\\-. The penultimate (or earlier) instar Leucoma salicis larva is induced to prepare a frail cocoon, as though for pupation, within a leaf package just before being mummified, and the mummy forms within that structure with only its setae in contact (Fig. 257). Although the parasitoid larva does make a ventral opening in the host’s thoracic region, through which fluid escapes and dries, the mummy is not thereby stuck down.

Diagnosis.

Antennal segments of ♀ 50-55 and head (except stemmaticum) entirely brownish yellow; scapus in lateral view distinctly oblique apically (Fig. 258); OOL 0.6 × diameter of posterior ocellus; occipital carina complete ventrally or nearly so (Fig. 268); vein 2-CU1 of fore wing 2.2-3.0 × vein 1-CU1 (Fig. 260); vein 1-SR linearly connected to vein 1-M and vein 1-M straight or slightly curved (Fig. 260); fourth metasomal tergite largely (superficially) granulate; length of fore wing 5-7 mm. Easily confused with Aleiodes varius ( Herrich-Schaeffer) , but this species has more antennal segments (♀: 66-71), malar space 0.6 × as long as height of eye, vein 2-CU1 of fore wing 1.6-1.8 × vein 1-CU1 and the occipital carina is reduced ventrally. Often also confused with Aleiodes gastritor (Thunberg) s. lat., but specimens of this species-group have many fewer antennal segments, the segments are more elongate and the pterostigma is often more or less dark brown or infuscate.

Description.

Redescribed ♀ (RMNH) from Nederweert, length of fore wing 5.9 mm, of body 7.1 mm.

Head. Antennal segments 54, length of antenna 1.2 × fore wing, its subapical segments about 1.8 × as long as wide and scapus in lateral view distinctly oblique apically (Fig. 258); frons superficially granulate and rugose, shiny; OOL 0.6 × diameter of posterior ocellus and rugulose; vertex granulate-rugulose, with satin sheen; clypeus rather high, convex, coriaceous; ventral margin of clypeus thick and gradually depressed (Fig. 268); width of hypoclypeal depression 0.4 × minimum width of face (Fig. 267) and face mainly coriaceous dorsally; length of eye 2.8 × temple in dorsal view and temple directly narrowed behind eye; occiput behind stemmaticum finely rugulose and occipital carina nearly complete medio-dorsally and ventrally (Figs 268-269); clypeus partly above lower level of eyes (Fig. 267); length of malar space 0.3 × height of eye in lateral view; eyes distinctly protruding (Figs 267-269).

Mesosoma. Mesoscutal lobes very finely coriaceous, with satin sheen, but medio-posteriorly rugose; notauli narrow, shallow and crenulate; prepectal carina rather lamelliform medio-ventrally, nearly reaching anterior border of mesopleuron and latero-ventrally angulate; precoxal area of mesopleuron with some short rugae medially (Fig. 262); mesopleuron above precoxal area (except large smooth and shiny speculum) superficially granulate, but dorsally extensively rugose; medially metapleuron coriaceous-rugulose, rather shiny; mesosternal sulcus narrow and rather deep, without carina posteriorly; mesosternum rather angulate posteriorly; scutellum finely coriaceous and non-carinate laterally; dorsal face of propodeum rather long and densely finely rugose, posterior face with some carinae and smooth in between, median carina complete, without tubercles, but somewhat angulate postero-laterally.

Wings. Fore wing: r 0.3 × 3-SR (Fig. 260); 1-CU1 horizontal, 0.35 × as long as 2-CU1; r-m 0.7 × 2-SR, and 0.4 × 3-SR; second submarginal cell elongate (Fig. 260); 1-SR angled with 1-M; cu-a rather oblique, not parallel with CU1b, slightly curved; 1 -M slightly curved posteriorly. Hind wing: apical half of marginal cell parallel-sided or nearly so (Fig. 261); 2-SC+R short and longitudinal; m-cu present as fold, unpigmented; M+CU:1-M = 15:12; 1r-m 0.7 × 1-M.

Legs. Tarsal claws yellowish setose; hind coxa superficially finely coriaceous, with satin sheen; hind trochantellus 2.7 × longer ventrally than wide; length of fore and hind femora 6.2 and 4.9 × their width, respectively (Figs 264, 266); inner apex of hind tibia without comb; length of inner hind spur 0.3 × hind basitarsus.

Metasoma. First tergite 0.9 × as long as wide posteriorly, flattened and latero-posteriorly lamelliform; first–second tergites and base of third tergite densely finely irregularly rugose and with median carina; second tergite robust and 1.5 × as long as third tergite (Fig. 263); medio-basal area of second tergite absent; second suture deep and distinctly crenulate; apical half of third tergite granulate-coriaceous, remainder of metasoma largely superficially coriaceous and rather shiny; fourth tergite largely with sharp lateral crease; ovipositor sheath largely densely setose and apically rounded.

Colour. Yellowish brown; apical third of antenna and stemmaticum (except medially) dark brown; palpi, malar space up to eyes, mandible, tegulae, fore and middle legs, hind trochanter and trochantellus and pterostigma pale yellowish (Fig. 260); medial veins dark brown and other veins brownish yellow; wing membrane subhyaline.

Variation. Length of fore wing 5.6-6.5 mm, of body 6.3-7.5 mm; antennal segments of ♀ 50(3), 51(13), 52(43), 53(79), 54(44), 55(7); colour and shape are very uniform in this species, probably because of absence of sexual propagation.

Notes.

Apart from a single specimen (reared from Leucoma salicis probably in Russia, with its mummy present) in poor condition in NMS, no males of Aleiodes pallidator have been seen; examined males identified by J. Papp or V.I. Tobias as Aleiodes pallidator belong to Aleiodes gastritor (Thunberg) s. lat. or to a species near Aleiodes abraxanae with darkened pterostigma, black stemmaticum and widened hind femur (e.g. females reported by Papp and Rezbanyai-Reser (1996, 1997)). The lectotype of Ichneumon pallidator has 53 antennal segments and the ocelli somewhat larger than OOL. The holotype of Rhogas ochraceus has the ocelli nearly twice OOL. Papp (1985) synonymised Aleiodes apiculatus (Fahringer, 1932) with Aleiodes pallidator , but we consider it to be a valid species.