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Revision of the World species of Xeris Costa (Hymenoptera: Siricidae)
CJAI 28 -- September 25, 2015
doi: 10.3752/cjai.2015.28
Henri Goulet1, Caroline Boudreault1 and Nathen M. Schiff2

3. Morphology

Schiff et al. (2012) discussed structural terms and most are reproduced here.

Wings. The veins of the fore and hind wings of Xeris are illustrated in Fig. A3.1. One of the most striking features of Siricidae is the incredible variation in wing venation, including the appearance or the disappearance of veins symmetrically or asymmetrically on both wings (e.g., see habitus images in Schiff et al. (2006)). Such variation is very rarely seen in other Hymenoptera, a group where wing veins are important for classification. Despite the exceptional variation in veins of Siricidae, wing venation was used in keys to subfamilies and genera (Schiff et al. 2012), usually supplemented with others features not associated with wings.

Female abdomen. The female abdomen has ten terga (singular: tergum) dorsally and seven sterna (singular: sternum) ventrally (Fig. B1.3). Terga 8–10 are conspicuously modified. Tergum 8 is greatly enlarged and extended posteriorly. Tergum 9 is the largest and has a deeply impressed dorsomedian impression, the median basin (Figs. A3.2 and B1.5), also known as the precornal basin. The lateral edges of the median basin are sharply outlined in the anterior 0.5 (Figs. A3.2 and B1.5). The anterior edge of the basin, when visible, is ridge-like and its lateral limits are outlined by two slightly convergent furrows. The maximum width of the basin at its base is measured between the outer furrows, which are usually clearly outlined and black on specimens with a reddish-brown abdomen. The posterior edge of the basin is outlined by a furrow between terga 9 and 10. Tergum 10 is modified as a long sharp horn-like projection, the cornus (Fig. A3.2). The cornus at its apex forms a short tube, probably used to assist adults to exit their larval host tunnels.

The abdomen posterior to sternum (Fig. B1.7) has an ovipositor that is covered by two sheaths when not in use.

Male abdomen. The male abdomen has eight terga dorsally and nine sterna ventrally (Fig. B1.4). Tergum 8 is slightly longer than the preceding terga (Fig. B1.6). The posterior edge of sternum 8 has a V-shaped median indentation or cleft, and sternum 9 extends posteriorly as a horn or cornus (Fig. B1.4). The lateral portion of the genitalia (the harpes) is usually visible between tergum 8 and sternum 9, but this was not studied.

Sculpture. In addition to structural terms for body parts, we opt for English terms to designate surface features, such as ridges (carinae), furrows (sulci), pits (concave and generally round surface features with or without a seta, but excluding the setigerous puncture just around a seta), and microsculpture.

Measurements. Because of the great variation in size (body length 9 to 35 mm) for most well sampled species, only ratios from measurements of two structures of a specimen were used. When possible, at least 30 specimens of each sex were measured. Means and standard deviations were calculated using Microsoft Excel software. The main measurements are the length of the basal and apical sections of the ovipositor sheath (Fig. B1.7) and those of tergum 9 and 10 in dorsal view (Fig. A3.2). The range of a measurement is given in the identification keys based on the calculation of two standard deviations. If a measurement falls within the overlap between values of the calculated two standard deviations, the character was rejected in favor of other characters, but if it is outside the range of the overlap portion, it is considered as a useful key character with a 1% chance of error.

For ovipositor characters with meristic values (e.g., the number of the annulus or annuli of the ovipositor aligned with the junction of the basal and apical sheath sections, the number of annuli with a very small pit on the ovipositor, and total number of annuli on the ovipositor), we recorded the range.

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