THE NEARCTIC SPECIES OF ACEROTELLA MASNER (HYMENOPTERA, PROCTOTRUPOIDEA, PLATYGASTRIDAE)

Abstract The genus Acerotella of the Nearctic region is studied. Six species are recognized, all new to science: A. acerina ♀ ♂ (Canada, U.S.A.), A. aceris ♀ ♂ (Canada), A. depressa ♀ (U.S.A.), A. gouleti ♀ ♂ (U.S.A.), A. nearctica ♀ ♂ (Canada, U.S.A.), and A. vockerothi ♀ (Canada). The generic diagnosis of Acerotella and key to Nearctic species are given. The higher classification, species-groups, and world distribution of Acerotella species are discussed.

The genus Acerotella was proposed to include four Palearctic species previously placed in Acerota Foerster which is now regarded as a subjective junior synonym of Inostemma Haliday (Masner 1964). The new species dealt with here represent the first described species of Acerotella from the Nearctic, and include the specimens reported by Muesebeck (in Krombein et al. 1979).

BIOLOGY, DISTRIBUTION, AND RELATIONSHIPS
No published host records are available for any species of Acerotella. However, Mr. H. J. Vlug (IPO, Wageningen) (in litt.) reared one Palearctic species from galls of a cecidomyid midge. It is highly probable that all species of Acerotella are primary parasites of various gall forming Cecidomyidae as inferred from known relationships in related genera of the subfamily Inostemmatinae. Two Nearctic species, viz. A. acerina n. sp. and A. aceris n. sp., are associated with sugar maple (Acer saccharum Marsh.). Numerous individuals of the latter two species were collected in spring from young leaves on lower branches and the young seedlings. The wasps were confined strictly to sugar maple and not encountered on surrounding plants or trees. A. nearctica n. sp. seems to be associated with lower vegetation, mainly the grasses (Poaceae) during late summer and fall. Although most species were recorded from low to mid altitudes, A. depressa n. sp. is described here from altitude over 3000 m.
The members of Acerotella are rather infrequent in collections. However, with the knowledge of association with certain plants and by using new methods of mass collecting we have accumulated over 300 specimens representing the six Nearctic species of Acerotella.
Four species of Acerotella are known in the Palearctic region; at present six new species are being described from the Nearctic region. None of the 10 species mentioned above seem to be Holarctic in distribution. I have also seen undescribed species of Acerotella from the Ethiopian region (Nigeria, Rhodesia), and the Neotropical region (Guatemala, Costa Rica, Trinidad W.I., Brazil) (CNC). However, the real distribution of Acerotella is probably much broader, perhaps worldwide.
Acerotella is a very distinct genus among the numerous genera of the subfamily Inostemmatinae (Platygastridae). It may be recognized by the downcurved apex of the submarginal vein (Fig. 5), the rounded posterior margin of the scutellum (Figs. 1, 3), and the generally depressed body. The pectinate spur of the fore tibia ( Fig. 18) as well as the relatively large, deeply declivous clypeus (Fig. 2) are reminiscent of Iphitrachelus Walker; however, in other respects Acerotella appears as a rather distinct genus. The non-horned females of Inostemma were in the past confused with Acerotella (Ashmead 1887, 1893: Fouts 1925Muesebeck and Walkley, in Muesebeck et al. 1951) as pointed out by Masner (1964). The following key is aimed to clarify this situation.
( 1 ) Submarginal vein near its apex slightly downcurved (Fig. 5 )    or abruptly 3-segmented (Fig. 10 There appear to be three species-groups in Acerotella, all of them represented in the Nearctic region, viz. aceris, boter, and evanescens. The aceris-group is the most distinct of the three, characterized by deep orange-yellow antennae in both sexes, light coloured legs, much elongate A3 in female antenna and relatively large clypeus. Two Nearctic species are assigned here, viz. A. aceris n. sp. and A. acerina n. sp. I also examined an undescribed species from Japan (coll. K. Yamagishi) that belongs here. Ecological data indicate that the members of this group are vernal, associated with maples (Acer spp.).
The boter-group and evanescens-group differ from the aceris-group in having antennae in both sexes dark brown or black, A3 in female antenna shorter, and clypeus relatively smaller. Boter and evanescens groups sharply differ from each other only in the female sex in that the antennal clava is subcompact and abruptly 3-segmented in boter-group, whereas the clava is not clearly differentiated in the evanescens-group. The boter-group is represented in the Palearctic region by A. boter (Haliday) and A. humilis (Kieffer), in the Nearctic region by A. nearctica n. sp. I also studied undescribed members of this group from Guatemala, Trinidad (W.I.), Brazil, and Nigeria (CNC). The evanescens-group has two species in the Palearctic region, viz. A . evanescens (Kieffer) and A. hungarica (Szelenyi), and three species in the Nearctic region, viz. A. depressa n. sp., A. gouleti n. sp., and A . vockerothi n. sp. The members of these two groups seem to be associated with herbaceous plants (e.g. grasses) rather than shrubs or trees.
MORPHOLOGY, ABBREVIATIONS, AND SYMBOLS All terms used in this paper are those used by Masner (1976). Measurements given in "relative proportions" refer to maximal length divided by maximal width (e.g. antennal segments, metasomatic tergites, etc.). The term "transverse" means that the object (e.g. the head) is wider than long.  Masner (1964), by original designation.

DESCRIPTIVE PART
Moderately elongate forms with body slightly to distinctly depressed dorsoventrally. Head transverse, subellipsoidal; cheeks not striate; mandibles bidentate; palpal formula 2-1; clypeus rather large, declivous and smooth; ocelli in low triangle, O O L distinctly shorter than both LOL and POL; eyes appearing glabrous (low magnification), with minute hairs (high magnification); antenna1 formula 10-10, in female clava either not abrupt, o r abruptly 3-segmented, and subcompact and A5-A7 very minute, in male with A 3 and A4 subequal in length; notauli either percurrent and often dilated posteriorly, o r abbreviated posteriorly, o r absent; scutellum flattened, almost semicircular, with posterior margin rounded, posterolateral corners not developed, wi.th 2 large pits in anterolateral corners; mesopleuron with deep depression; sternaulus either well developed o r incomplete; metanotum unarmed; propodeum without membrane, hairy, with 2 short sub-parallel or parallel keels at meson; fore wing with submarginal vein gently downcurved at apex; marginal cilia very short; tarsal formula 5-5-5, tibia1 spur formula 1-2-2, spur o n fore tibia pectinate, shortly bifurcate apically; metasoma i n female elongate, at least a s long as head and mesosoma combined, with 6 visible tergites, T 1 always without horn; T6 usually elongate and almost truncate at apex, rarely broadly triangular, and almost pointed apically; T2 largest of all tergites, usually as long a s T3-T6 combined o r longer, with short striae and/or median sulcus at anterior margin; metasoma i n male with 7 visible tergites.

Females
(1) A l , most of antennae, and at least fore legs bright orange-yellow; A1 distinctly longer than frons between toruli and anterior ocellus; vernal species associated with maples (Acer spp. (2) Antenna more slender, with A7-A9 as long as wide or slightly elongate, A10 1.5 times as long as wide, A8 and A9 separated by distinct constriction ( (4) T2 as long as wide, shorter than T3-T6 combined, not distinctly striate basally; body remarkably depressed, 1.7 times wider than high, with scutellum in lateral view levelled Female. Length 1.5 mm. Body black, with antennae and legs predominantly light coloured; A1-A4 bright orange-yellow, A5-A10 gradually darkened, from dirty yellow to light brown in A9 and A10; fore trochanters, tibiae, and tarsomeres 1-4 concolorous with A1-A4, femora yellowish brown, coxae dark brown; middle and hind legs darker brown, mid-femora lighter than mid-tibiae except for upper tibia1 apices that are lighter, hind legs entirely dark brown; wings clear.
Mesosoma moderately flattened, wider than high (45:32), sides of prothorax smooth except in upper (shoulder) area which is reticulate, the anteromedian part slightly longitudinally mgulose; mesoscutum finely coriaceous, almost smooth in posterior half between notauli (in front of scutellum); notauli percurrent, though fine and shallow, not distinctly dilated posteriorly but partly obsolete in front of scutellum, with anterior pits deep; anterior parallel lines finely indicated; scutellum coriaceous, with anterior pits large and deep; mesopleuron mostly smooth, with mesopleural depression deep, with narrow band of coriaceous sculpture dorsad of sternaulus, the latter fine but complete; propodeum hairy, with median keels slightly diverging posteriorly; femora reticulate, the hind ones in particular.
Male. Differs from female mainly in secondary sexual characters such as the antennae (Fig. 7)  BIOLOGY. The host is unknown but is presumed to be a common gall forming cecidomyid associated with sugar maple (e.g. Dasyneura communis Felt). Adult wasps were encountered on maple leaves during a relatively short period in each locality (about a week).
VARIABILITY. The total body length varies between 1.1 and 1.5 mm. The smaller individuals ( 9 8 ) tend to have antennae generally shorter, with flagellomeres less elongate than in the holotype and the allotype. However, even in extreme cases readings do not overlap with those obtained in A. acerina. Notauli may be more or less distinctly dilated posteriorly in some individuals. Striation and the median sulcus at the base of T2 may also vary in that sulcus may become weak or even missing in some individuals. Colour of antennae and legs may be more xanthic in some individuals and less in others; however, A1 and most of flagellum is always orange-yellow even in generally darker specimens.
REMARKS. This species forms together with A . acerina a very distinct species-group within Acerotella. The two species may be conveniently distinguished from each other in the female sex by differences in antennae (Figs. 6,8), and similarly in the male sex (Figs. 7,9). The sculpture of the vertex (i.e. the interocellar triangle) is generally finer in A. aceris than in A. acerina.
The name proposed refers to maple (Acer) with which this new species is associated.
Male. Differs from the female in secondary sexual characters; from males of A . aceris in having antenna distinctly shorter, with flagellomeres A6-A9 only 1.2 times as long as wide (Fig. 9). VARIABILITY. Body length in specimens examined varies between 1.1 mm and 1.4 mm. Smaller individuals tend to have sculpture of vertex finer, almost identical with that on occiput. Median sulcus on T 2 is shorter in some individuals than in the holotype. Fore legs and A2-A5 may be bright orange-yellow in some individuals. Posterior half of mesoscutum (between notauli) may be partly sculptureless in smaller individuals.

REMARKS.
A. acerina and A. aceris can be distinguished primarily by antenna1 characters: for females see Figs. 8 and 6 ; for males see Figs. 9 and 7 .

. Acerotella nearctica n . sp.
Head transverse (20:38), slightly narrower than mesosoma across tegulae (38:43); lower third of frons reticulate, upper two thirds finely coriaceous; vertex and particularly occiput more coarsely reticulate; occipital carina sharp and complete, with minute crenulae inwardly; small pit on occiput in front of middle of occipital carina; clypeus smaller than in the acerisgroup; eyes with minute scattered hairs; eye height smaller than interorbital space (15:23); posterior ocelli distant from inner orbits by less than half of ocellar diameter; antenna as in Fig. 10, with abrupt 3-segmented clava; A1 as long as frons between toruli and anterior ocellus.
Mesosoma distinctly flattened, wider than high (44:26); mesoscutum finely coriaceous except for distinctly longitudinal sculpture in posterior 114 in front of scutellum (between notauli); notauli percurrent but partly obsolete in posterior 114 where shallowly dilated and longitudinally striate; anterior parallel lines indicated; sternaulus not developed but the corresponding part of mesopleuron coriaceous, with mesopleural depression smooth; scutellum evenly coriaceous; two median keels of propodeum perfectly parallel; fore wings not surpassing tip of metasoma when resting; hind femora partly smooth, partly coriaceous.
BIOLOGY. The host is unknown; however, a series of individuals were swept from brome grass (Bromus sp.) in Ottawa and more individuals were swept from miscellaneous grasses in Ontario and Quebec during late summer and fall.
VARIABILITY. This melanic species seems to b e chromatically stable. Slight variation has been observed in the intensity of the longitudinal sculpture in posterior half of mesoscutum; sculpture tends to b e more delicate i n smaller individuals. It seems that the apical segment of the metasoma (T6, S6) in the female may b e partly telescoped as in some individuals it appears either chorter o r longer than in the holotype. Smaller males tend to have A6-A9 slightly transverse instead of slightly elongate as compared with larger males. REMARKS. This is at present the only species of the boter-group in North America. It differs from A. boter as follows:  Female. Length 1.4 mm. Black, including antennae and legs, except for brown apices of tibiae and tarsi; wings slightly tinted.
Head distinctly transverse (18:38), as wide as mesosoma across tegulae; frons, vertex, and occiput evenly and finely coriaceous, with minute scattered punctures; a small smooth circular area on frons in front of anterior ocellus; occipital carina complete, with no visible crenulae, occipital pit shallow and minute; temples strongly receding; clypeus relatively low; frons between toruli and anterior ocellus as long as A l ; interorbital space larger than eye height (25:15); posterior ocelli distant from inner orbits by about half of ocellar diameter; eyes with minute scattered hairs; antenna as in Fig. 12, only gradually incrassate towards apex, with non-abrupt 4-5 segmented clava.
Mesosoma remarkably depressed, 1.7 times as wide as high, flattened dorsally, with scutellum at same level with mesoscutum; mesoscutum partly sculptured, partly smooth, with fine coriaceous sculpture and scattered setigerous punctures on lateral lobes in anterior part of middle lobe and along inner course of notauli, with larger smooth area on mid-lobe (between anterior part of notauli) and virtually all posterior half of mid-lobe in front of scutellum; notauli well indicated in anterior 213, obsolete posteriorly; anterior parallel lines not developed; scutellum with streak of very delicate coriaceous sculpture in middle part, smooth at sides (below pits); sternaulus complete though delicate; mesopleural depression smooth; metapleuron hairy; median keels on propodeurn very short; fore wing not surpassing tip of metasoma; hind femora slightly incrassate, smooth proximally, coriaceous distally.

Fig. 14
Female. Length 1.3 mm. Black, with antennae dark brown to black, legs dark brown, with apices of tibiae and tarsi lighter; wings slightly tinted.
Head moderately transverse (18:32), as wide as mesosoma across tegulae; frons, vertex, and occiput evenly coriaceous, however, with sculpture somewhat coarser than in A. depressa, with no smooth area in front of anterior ocellus; occipital carina complete, occipital pit not distinct; clypeus relatively low; frons between toruli and anterior ocellus as long as A l ; interorbital space larger than eye height (21:16); posterior ocelli distant from inner orbits slightly more than by one ocellar diameter; eyes appearing glabrous; antenna (Fig. 14) moderately incrassate towards apex, with no abrupt clava, with A9 and A10 approximated.
Mesosoma only about 1.2 times wider than high, with scutellum in lateral view topping mesoscutum; mesoscutum evenly coriaceous except for smaller smooth area posteromedially (in front of scutellum); notauli visible in anterior half of mesoscutum, obsolete posteriorly, not distinctly dilated and not longitudinally striate; scutellum evenly coriaceous; sternaulus partly indicated in front of mid-coxa; mesopleural depression partly with fine longitudinal sculpture; metapleuron hairy; median keels of propodeum short; fore wing leaving the tip of metasoma uncovered; hind femora not distinctly incrassate, smooth.
Differs from A . vockerothi in following characters: Coriaceous sculpture of frons extremely fine, leaving an almost smooth area in front of anterior ocellus; vertex with coarser coriaceous sculpture, occiput with coriaceous-reticulate sculpture; occipital carina weak but complete; occipital pit absent; OOL slightly less than ocellar diameter; A3 rather slender, 2.5 times as long as wide, antennal clava non-abrupt, 4-segmented, with A9 and A10 approximated but with slight constriction in between; notauli delicate and shallow, better indicated in anterior 213; posterior half of median lobe of mesoscutum (between notauli) smooth; scutellum finely coriaceous in anterior 213, smooth in posterior 113; metasoma as long as mesosoma and head combined; T2 with short striae and long median sulcus extending to basal half of the tergite.

REMARKS.
A . gouleti belongs to the evanescens-group. It differs from the other two Nearctic members of this group as follows: from A . depressa by considerably convex body, deep long median sulcus on T2, T2 distinctly elongate and head less transverse; from A . vockerothi by characters mentioned in the key but also by general shape of antennae, shorter metasoma, etc. The male of A . gouleti differs from the male of A . nearctica apart from characters mentioned in the key, by considerably long whitish hairs on flagellomeres A3-A10. It is my pleasure to dedicate this new species to Dr. H. Goulet (Biosystematics Research Institute, Ottawa), who collected the first specimen in southern Illinois.