Melittobia chalybii Ashmead, 1892

Matthews, Robert W. & González, Jorge M., 2008, The acasta conundrum: Polymorphism and taxonomic confusion within the parasitoid genus Melittobia (Hymenoptera: Eulophidae), Zootaxa 1854, pp. 45-54 : 47-48

Melittobia chalybii Ashmead, 1892

Based on male variability in field collections, we initially hypothesized that M. chalybii might represent an early- or late-maturing variant among the M. femorata brood. Unfortunately, the seven males in Ashmead’s M. chalybii syntype series were found to be in relatively poor condition, making it difficult to properly assess critical characters. We also found that there were puzzling discrepancies between Dahms’ description and figures, and our observations of key characters on Ashmead’s specimens. However, these incongruities appear to stem from the fact that Dahms’ (1984a) drawings and description of the M. chalybii male were made not from the type series, but instead from two males he mounted on a slide (deposited in QM) taken from a vial of reared Melittobia vouchers deposited by Schmieder in the USNM. We have shown previously that Schmieder (1933 and later papers) made multiple collections and incorrectly applied the name M. chalybii to all, though in reality he may have had as many as four different species ( González & Matthews 2002); indeed part of Schmieder’s material was included among the specimens Dahms studied and named as M. evansi . While Dahms properly designated a male lectotype for M. chalybii from Ashmead’s syntype series (see below), apparently his description and illustrations of the male were entirely based on the slide-mounted Schmieder material.

Comparative examination showed that the males that Dahms mounted from the vial of Schmieder’s vouchers were apparently first-brood individuals; in their antennae form, wing shape, and middle femur setae pattern, they agree closely with our first-brood M. femorata males ( Fig. 2 ). In fact, Dahms’ drawing of the antennal flagellum ( Dahms 1984b, his Fig. 12) of the slide-mounted, unidentified acasta group males (which specimens we also examined in this study) nearly matches that of our first-brood M. femorata specimens ( Fig. 2 a), making it likely that these are first-brood specimens conspecific with M. femorata (= M. megachilis , see below). However, there was considerable variation in the first funicular segment among the first-brood males ( Fig. 2 a–c); this would result in some specimens keying mistakenly to Dahms’ couplet 11, forcing a choice of either M. scapata or M. evansi .

Despite this male variability, however, our reared females from the early and late samples of MF brood were virtually identical in all morphological characters and measurements, and none shared the suite of morphological characteristics that Dahms used to distinguish M. chalybii . Dahms’ (1984a) key to Melittobia females, couplet 5, separates M. chalybii from the rest of the acasta group as having “eyes densely clothed with long setae” versus “eyes relatively bare, with a few short scattered setae.” Eye hairiness varied from absent to scant in our field-collected and laboratory-reared samples, but was never as distinct and dense as we confirmed for the six females in the M. chalybii syntype series. In addition to hirsute eyes, head shape was generally more rounded, particularly the genal-clypeal margin. Compared to M. megachilis and M. femorata , the female antennae of M. chalybii have distinctly fewer multiporous plate sensilla on the three funicle segments according to Dahms (1984a). Comparison of the M. chalybii type material to our reared and collected M. femorata revealed that in the type material, the submedian lobes of the scutellum had more setae (3 to 5 versus 2–3 in ours), and the submarginal vein of the forewing had more setae (5 to 6 versus 3 to 5 in ours). Thus, based on our measurements and Dahms’ descriptions, support for synonymy of female M. chalybii and M. femorata (= M. megachilis , see below) is equivocal.

Therefore, at this time it seems premature to synonymize M. chalybii under M. femorata (= M. megachilis , see below), although the possibility remains open that it is a variant of M. megachilis . The fact that M. chalybii were essentially nonexistent in our T. politum host samples suggests that to better understand these supposedly common polyphagous parasitoids, future field studies should focus upon different host complexes and habitats (e.g., cavity nesting aculeates). Whether the apparent morphological differences reflect true species differences or simply nutritionally or environmentally induced variation awaits further research.

A footnote to all this is the matter of the type locality of M. chalybii , which Ashmead listed only as “Virginia” in his original description. As was often customary in that era, he did not state how many specimens were included in his type series, nor did he designate a holotype. In the USNM collection there are 14 pointmounted specimens, six females and eight males that appear to constitute the material from which M. chalybii was described.. Only some of the specimens bear Ashmead’s handwritten labels and only seven bear a typewritten “Va.” label (we suspect that they were added by subsequent workers, apparently a common practice in the early 20th century). Dahms (1984a) studied six “Va.” labeled specimens (3 males and 3 females), and designated one male as lectotype, and the other five specimens as paralectotypes. In his listing of these types Dahms’ added new locality information, "Bladensb. VA”, he found on Ashmead’s handwritten labels on some specimens. However, both Ashmead and Dahms were in error because Bladensburg is not in Virginia, but is a suburb of Washington, District of Columbia, falling in Maryland. (In fairness to Dahms, Ashmead's flowing handwriting of the letters "Md" (or perhaps they really were “Va”) could easily be misread as "Va".)

Figures

FIGURE 2. Variation in M. megachilis from a single culture. a – c: antennae of different first-brood males, showing range of variation. d: antenna of second-brood male. e: forewing of first-brood male. f: forewing of second-brood male. g: middle leg of first-brood male. h: middle leg of second-brood male.