Necremnus croton (Walker, 1839)

Gebiola, Marco, Bernardo, Umberto, Ribes, Antoni & Gibson, Gary A. P., 2015, An integrative study of Necremnus Thomson (Hymenoptera: Eulophidae) associated with invasive pests in Europe and North America: taxonomic and ecological implications, Zoological Journal of the Linnean Society 173 (2), pp. 352-423 : 390

NECREMNUS CROTON (WALKER) ( FIGS 72–77 )

Eulophus croton Walker, 1839: 182 . ♀ lectotype (BMNH, here designated).

Necremnus croton ; Graham, 1959: 184.

Type material

There is no indication in the original description of whether the type series consisted of more than a single female. The original description stated that the species was collected near London. The BMNH has a single, card-mounted female ( Fig. 72 ) with the following five labels: (1) a circular, purple-bordered label with ‘LECTOTYPE’; (2) a rectangular label with ‘ Croton ’ handwritten on one side and ‘[?]ENT GAR’ printed on the other side; (3) a rectangular label with ‘ Pteromalus Croton Walker’ handwritten on one side and ‘Stood under this name in old B.M. Coll. C. Waterhouse.’ printed on the other side; (4) a rectangular label with ‘ Eulophus Croton Walker LECTOTYPE: ♀ M. de V. Graham det. 1958’ partly printed and handwritten; and (5) a square label with ‘B.M. TYPE HYM. 5.2501’. The lectotype is entire, but the head is collapsed and the flagellum is mostly covered in glue ( Fig. 73 ). As Graham did not validly designate a lectotype through publication under ICZN rules, in order to stabilize the concept of the name we designate this female as the lectotype of E. croton .

Description

Female (lectotype)

Body ( Fig. 72 ) almost 1.5 mm in length. Head strongly collapsed, but primarily dark brown with very slight violaceous lustre under some angles of light. Antenna ( Fig. 73 ) with scape similarly dark as flagellum; length of flagellum + pedicel at most about 1.2 × width of head (head strongly collapsed and width estimated); flagellum with length of F1 + anelli about 1.5 × length of pedicel and about 2.1 × as long as wide, F2 about 1.8 ×, F3 about 1.5 ×, and clava about 2.6 × as long as wide. Mesosoma ( Figs 72, 74 ) with mesonotum bluishgreen to purple under some angles of light, but dorsellum and propodeum more distinctly green ( Fig. 75 ); tegula uniformly yellowish brown. Mesonotum ( Fig. 74 ) with mesoscutum distinctly mesh-like reticulate; scutellum entirely, distinctly reticulate, the reticulations somewhat larger and more elongate laterally than along midline. Fore wing ( Figs 72, 76 ) hyaline; basal cell and speculum posteriorly delimited by complete rows of setae ( Fig. 77 ); speculum broadly bare dorsally; approximate ratio of cc: mv: stv: pmv = 53:36:15:[?]. Legs ( Fig. 72 ) with profemur dark brown, protibia and protarsus lighter brown with knee and tibia dorsolongitudinally pale; meso- and metafemora dark brown, metatibia brown except extreme base and apex pale, but mesotibia with about basal half more brownish yellow, and meso- and metatarsi with basal two tarsomeres pale and apical two tarsomeres brownish. Metanotum with dorsellum distinctly reticulate ( Fig. 75 ). Propodeum ( Fig. 75 ) with entire median carina, otherwise reticulate to more reticulate-imbricate toward spiracles; spiracle comparatively small, separated from posterior margin of metanotum by about minimum internal diameter. Gaster ( Fig. 72 ) brown; about 1.9 × as long as wide and about 1.25 × length of mesosoma; syntergum short.

Male

Unknown.

Distribution

England, Macedonia, Sweden, Turkey ( Noyes, 2013).

Hosts

Pseudobankesia macedoniella (Rebel) ( Lepidoptera : Psychidae ) (Boucˇek, 1977).

Discussion

Females of N. croton and N. capitatus Boucˇek differ from those of other described Necremnus (except N. propodealis Boucˇek, which has pale legs beyond the coxae) by their comparatively strongly sculptured mesosoma ( Fig. 74 ), particularly the propodeum ( Fig. 75 ). Accurate measurement of the length of the postmarginal vein of the lectotype of N. croton is questionable because the wing is glued to the card and the exact apical extent of the vein is not clear ( Fig. 76 ), although the vein appears to be relatively short compared with the stigmal vein. Askew (1964) stated that both N. croton and N. capitatus have the postmarginal vein only slightly longer than the stigmal vein. Females of the two species are very similar, but according to Askew (1964) N. capitatus females have extensively pale tibiae with the meso- and metatibiae at most infuscate only apically, and a less elongate body (gaster about 1.4 × as long as wide and only about 0.77 × the combined length of the head and mesosoma), but with longer funicular segments (F1 at least 3 × as long as wide). The lectotype of N. croton has the gaster about twice as long as wide and subequal in length to the head and mesosoma ( Fig. 72 ). However, the gaster is strongly collapsed dorsally, which may result in a slightly greater length to width ratio, and the head is also collapsed so as to appear strongly transverse in dorsal view ( Fig. 72 ), which probably results in a somewhat longer gaster to head plus mesosoma ratio than in fully inflated, natural specimens. Perhaps a more reliable feature is that F1 + anelli is only about 2.1 × as long as wide (about 1.9 × excluding anelli, Fig. 73 ). Additionally, at least the metatibia is infuscate except very narrowly basally and apically. The mesotibia has a similar colour pattern except about the basal half is somewhat paler, more brownish yellow ( Fig. 72 ).

Figures

Figures 72–77. Necremnus croton, ♀ lectotype. 72, dorsal habitus; 73, antennae; 74, dorsal mesosoma; 75, metanotum and propodeum; 76, fore wing; 77, fore wing base.