ISSN 1911-2173

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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

1. Use of keys

            Specimen condition and preparation. Clean specimens (greasy specimens are quite common in collections) with wings slightly open (needed to view the dorsal surface of the abdomen) are preferable when possible. At least one antenna and one leg of each pair must be present and complete.


It is often important to know the sex of the specimen to be keyed. Males and females are easily separated. The main sexual differences for all species are on the pronotum, the hind leg, and the abdomen.

Female features are:

  • Long sword-like sheath ventral to abdominal segment 9 and posterior to sternum 7 covering the ovipositor (Fig. B1.7).
  • Abdomen large, particularly terga 8 and 9 (Figs. B1.3 and B1.5).
  • Tergum 9 with a very large median impression (median basin) (Fig B1.5).
  • Tergum 10 extending posteriorly as a long horn (cornus) (Figs. B1.3 and B1.5).
  • Setae on dorsal surface of pronotum abundant and long (Fig. B1.1 and insert).
  • Hind leg in lateral view similar in proportions but longer than fore and middle legs (Fig. B1.8).

Male features are:

  • Abdomen without sword-like extension (Figs. B1.4).
  • Abdomen slender and apical tergum similar to but a little longer than preceding terga (Figs. B1.4 and B1.6).
  • Tergum 8 (the last tergum) without a median impression (Fig. B1.6).
  • Sternum 9 (the last sternum) extending posteriorly as a short horn (cornus) (Fig. B1.4).
  • Setae on dorsal surface of pronotum absent, or extremely small and difficult to see (Fig. B1.2).
  • Metatibia and metatarsomere 1 in lateral view clearly enlarged relative to pro- and mesotibia and pro- and mesotarsomere 1 (Fig. B1.8).


Male identification does not require dissection; female identification occasionally may require it. The complete ovipositor can easily be pulled out of its sheaths either after relaxing a dried specimen for about 36 hours in a very humid atmosphere (in a closed container with a wet paper towel or sponge) or immediately before or after pinning an alcohol preserved specimen. To see most or all the ovipositor of a relaxed or recently mounted alcohol preserved specimen, insert an insect pin between the ovipositor and the apical section of the sheath and gently slide the pin toward the base of the sheath. This will force the ovipositor out of the sheath. Ensure that the ovipositor remains out of the sheath. Use a fine paintbrush dipped in 95% alcohol to remove any dirt from the ovipositor. A concentrated solution of detergent in water may be necessary to remove persistent oil drops. The specimen is now ready to be examined and keyed.

Lighting. The light source is important. The best light is diffused light either directly from a daylight fluorescent light (13 watts is usually satisfactory) or produced with a semi-opaque plastic between the light source and the specimen. Good diffusion is achieved when the plastic is about 20 mm from the specimen. This type of lighting eliminates all or most glare from smooth surfaces. Such lighting makes structural features very clear and has been used throughout our work as illustrated in the numerous figures. We use a small (5 by 7 cm) piece of transparent plastic (Mylar) placed vertically on a base of modeling clay about 20 mm from the specimen to provide a sharp and glare free image (e.g., ovipositor pits). A dissecting microscope with a magnifying range of 40–60 times is recommended to view most structures clearly.

Key construction. Each couplet is arranged in contrasting pairs of statements labelled, respectively, with upper and lower case letters. Each statement almost always describes one feature of a character. For example in couplet 1C and 1c (e.g., relative size of eye height relative to head height) different expressions of the same character would be found. Information that is not compared in the alternate part of the couplet is given in brackets (e.g., additional characters, notes and range). Clarification notes are given in parentheses. Almost all statements of each couplet are illustrated. Two figures with the same statement code show a range of variation for a character state. The illustration shown is not necessarily that of the species of the specimen at hand, but is a similar expression of the character state to be observed. Therefore, other structures in the figure should be ignored as they do not necessarily represent those of the specimen being keyed. Plates of figures are organized so that the contrasting statements of each character are adjacent to one another. Arrows and morphological terms are added for clarity.

Table of contents Abstract Introduction Materials and Methods Biology Hosts Parasitoids Morphology Key DNA References Citation Appendices PDFs