Nathan M. Schiff, Henri Goulet, David R. Smith, Caroline Boudreault, A. Dan Wilson, and Brian E. Scheffler
The following is intended as an overview of adult siricid structure wherein terms used in this work are defined and illustrated. Terms for structures mostly follow Huber and Sharkey (1993), but a few terms are specific to sawflies and Siricidae. English terms are used for the female genitalia for which the numerous figures in Ross (1937) were consulted. The terms used by Wong (1963) are also given in parenthesis.
The body consists of three distinct sections: the head, thorax and abdomen (lateral habitus of female Fig. A3.1 and lateral habitus of male Fig. A3.2).
The head consists of the head capsule, eye, antenna, and mouthparts (Fig. A3.1).
- Head capsule. The head capsule is divided into several regions that usually have indistinct boundaries. In frontal view the clypeus is the region below and between the antennal sockets (Fig. A3.4). The face is the region lateral to the clypeus ventral to the antennal sockets which is mostly composed of the antennal scrobe (Fig. A3.4), a depression that receives the antennal scape when it is appressed to the head. The frons is the region between the inner edges of the eyes between the ventral edges of the antennal sockets and median ocellus (Fig. A3.4). The vertex is the region between the ventral margin of the median ocellus and highest part of the head capsule, which above the eyes in dorsal view extends laterally to about outer margin of each eye (Figs. A3.4, A3.6). The vertex has three ocelli, the median ocellus, and two lateral ocelli, but most Siricidae lack the clearly differentiated postocellar furrow behind each lateral ocellus that is more apparent in most other sawflies. The gena (often referred to as temple) is the surface posterior to the eye in lateral view, including the surface below the eye (Fig. A3.5). Although the occiput is not clearly differentiated from the gena and vertex it is considered as the posterior surface of the head capsule (Figs. A3.5, A3.6). The occiput surrounds the foramen magnum (an opening between the head and the thorax) and meets ventrally along the occipital junction.
- Antenna. The antenna is divided into three principal sections, the scape, pedicel and flagellum. Little is described in the work for the first two sections but various character states of the flagellum are described. The flagellum consists of 4 to about 30 flagellomeres that are numbered consecutively following the pedicel (Fig. A3.11).
- Mouth parts. The labrum is a very small, finger–like structure that is normally concealed under the clypeus between the mandibles. The labial palp (Fig. A3.5), though very short, consists of two or three palpomeres that are clearly visible below the mandible. The maxillary palp consists of a single palpomere that is hidden under other mouth parts.
The thorax consists of three major sections, the prothorax, mesothorax and metathorax, including the wings and the legs.
- Prothorax (Figs. A3.1, A3.3). The prothorax is the anterior segment of the thorax. It consists of a dorsal, transverse sclerite, the pronotum, that laterally extends ventrally toward the procoxae. On either side ventral to the pronotum is the propleuron. The prothorax lacks wings but bears a pair of fore legs.
- Mesothorax (Figs. A3.1, A3.3). The mesothorax is the middle segment of the thorax. The dorsal sclerite, the mesonotum is divided by the transscutal fissure (we are not certain that the broad furrow is really this structure seen in later Hymenoptera lineages, but its starting and ending point match) into an anterior mesoscutum and posterior axilla and mesoscutellum. The lateral surface of the mesothorax is the mesopleuron, which is differentiated into an anterior mesepisternum and posterior mesepimeron. The mesothorax has a pair of fore wings and a pair of mid legs.
- Metathorax (Figs. A3.1, A3.3). The metathorax is the posterior segment of the thorax. The dorsal sclerite of the metathorax, the metanotum, bears a pad, the cenchrus, anterolaterally (Fig. A3.3). The lateral surface of the metathorax, the metepisternum and metepimeron, are not referred to in this work except for color patterns. The metathorax has a pair of hind wings, and a pair of hind legs.
- Wings. The characteristic wing cells and veins of the fore and hind wings are illustrated in Figs. A3.29 & A3.30. One of the most striking features of Siricidae is what appears to be incredible variation in wing venation, including the appearance or the disappearance of veins symmetrically or asymmetrically on either wing. Such variation is very rarely seen in other Hymenoptera, a group where wing veins are important for classification. Habitus images in Schiff et al. (2006) provide many examples of variation in siricid wing venation and although this was not their intended goal, it is easy to observe the venation anomalies among the nicely spread specimens.
Some veins of Siricidae are considered as part of the ground plan of the Hymenoptera such as the basal portion of vein 2A and the presence of fore wing vein cu1. The tendency for veins to appear or disappear in Siricidae might suggest atavisms, i.e., reactivation of long lost character states or a reversal to an ancestral state but we are more tempted to view the feature as newly created within the Siricidae. For example, we have seen specimens with a partial cross vein found basal to vein cu1, for which there is no equivalent in other Hymenoptera. Despite the exceptional variation in veins of Siricidae, we have used wing venation in keys to subfamily and genera. However, where possible we supplement these wing characters with others features not associated with wings.
- Legs (Figs. A3.1 and A3.2). Each leg consists of five sections, the coxa, trochanter, femur, tibia and tarsus. This last section, the tarsus, consists of five tarsomeres that are numbered consecutively from the tibia. The prefixes “pro”, “meso” or “meta” are used to indicate which thoracic segment each leg segment belongs (see hind leg in Fig. A3.2). The tarsal pads (pulvillus/pulvilli), also known as plantulae (Schulmeister 2003), are membranous surfaces ventrally on tarsomeres 1-4 (Figs. A3.27 & A3.28) that are white and convex, and extend very slightly anterior to the apical margin of the tarsomeres (Schulmeister, 2003). In some species, the tarsal pads are relatively short (Fig. A3.28). The tarsal pads can best be observed on metatarsomere 2 because the tarsi of the fore and mid legs are often folded close to the body and the tarsal pads are then hidden. Observation of the tarsal pads is important for identification and is usually easy unless the specimen is covered with oil. A fine paint brush moistened with 95% ethanol can be used to help remove oil.
The abdomen consists of several segments that are numbered consecutively following the thorax. Tergum 1 (first abdominal tergum, Fig. A3.3) has a deep longitudinal cleft medially, it is not fused to the metapleuron laterally and although it is fused dorsally to the thorax it is separated from it by a deep furrow along its anterior edge. Structure of the abdomen of males and females otherwise differs and for this reason they are discussed separately below.
- Female abdomen.
- The female abdomen has ten terga (singular: tergum) dorsally and seven sterna (singular: sternum) ventrally (Fig. A3.7), of which terga 8-10 are conspicuously modified. Tergum 8 is greatly enlarged and is extended posteriorly. Tergum 9 is the largest tergum and has a deeply impressed dorsomedial impression, the median basin (Fig. A3.3), also known as the precornal basin. The lateral edges of the median basin are sharply outlined only near its base to almost to the posterior edge of tergum 9 (Fig. A3.12). 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 outlined in black. The posterior edge of the basin is a furrow between terga 9 and 10, which is often interrupted medially in specimens of Sirex. Tergum 10 is modified as a sharp horn–like projection, the cornus. The cornus varies in shape, but its apex forms a short tube (Fig. A3.9) that probably assists adult movement in their larval host tunnels.
- The abdomen posterior to sternum 7 has an ovipositor that is covered by two sheaths when not in use.
- Each sheath consists of three parts: a basal small sclerite dorsobasally (valvifer 1), a long basoventral sclerite (valvifer 2), and an apical sclerite (valvula 3). In this work only the last two sclerites are referred to, as basal section and apical section of the sheath (Fig. A3.26). The length of these two sections is compared to one another and to the fore wing length.
- The ovipositor consists of a fused pair of dorsal lances (valvula 2) and a pair of ventral lancets (valvula 1) (Figs. A3.16 & A3.17). The lance and lancet slide along each other and help move the egg along the ovipositor as well as drilling in wood and removing the resulting sawdust for egg deposition. The part described in this work is the lancet, which is divided in numerous sections that we called annuli. Lancet annuli usually are outlined by vertical to slanted ridges (Fig. A3.17). The annuli are usually present to the base of the lancet, but in some species several basal annuli are difficult to distinguish because each annulus is barely outlined dorsally near the lance. The number of annuli varies within species and between species. The apex of the lancet consists of four annuli each with a large tooth (Fig. A3.17). Some or all of the annuli, anterior to these four apical annuli, have a pit adjacent to the line or ridge of the annulus (Fig. A3.17). The size of the pit varies from 0.1-0.7 times the length of the annulus (Figs. A3.18 – A3.21), but regardless of whether small or large the pits may gradually become markedly smaller anteriorly or even disappear suddenly or gradually toward the base. The pits may also be wide to narrow, from 2.5-1.0 times as long as high (Figs. A3.18-A3.21). To photograph the lancet for the best range of tonalities, we oriented it toward the light. Therefore contrary to normal, we present images of the ovipositor in lateral view but with the lancet at the top rather than at the bottom of the image. This view is most similar to what will be seen by users when viewing a female abdomen in lateral view with the ventral surface facing away from the user (toward the top of the page in most of our images).
- Male abdomen.
- The male abdomen has eight terga dorsally and nine sterna ventrally (Fig. A3.8). Tergum 8 is slightly longer than the preceding segments. The posterior edge of sternum 8 is narrowly or widely concave and sternum 9 is extended posteriorly as a horn or cornus. The lateral portion of the genitalia (the harpes) is usually visible between tergum 8 and sternum 9, but this was not studied here. In addition to structural terms for body parts, some terms designate surface features, such as ridges (plural carinae, singular carina), furrows (plural sulci, singular sulcus), pits (punctures) and microsculpture. The meaning of ridges and furrows are clear but pits and microsculpture require more discussion.
- Pits are concave impressions consisting of multiple cell. Each pit is usually associated with a sensory cell, which in most pits of Siricidae is a seta or seta-like mechanoreceptor. We use the word “pit” rather than the more common expression “puncture” because it refers to a concave impression not a hole through the cuticle. Pit sizes are compared to the maximum diameter of a lateral ocellus (e.g., for a small pit, the diameter may be 0.1 times the diameter of a lateral ocellus whereas for a large pit it may be 0.5 times times the lateral ocellus diameter), and the density is expressed as the number of typical pit diameters between pits (Figs. A3.22 & A3.23). Pits in Siricidae are usually simple concave and round impressions, but those on the mesoscutum and mesoscutellum may be very dense and polygonal with their edges becoming ridges of various heights so as to look like irregular craters or a fish net (Fig. A3.24). An unusual type of pit in Siricidae is the “pegged pit”, which is found on at least the ventral surface of most flagellomeres (Fig. A3.25). Each pegged pit has a sensory cell.
- Microsculpture consists of small cellular imprints on the cuticle within which there is no sensory cell. Typical microsculpture of insects is roughly hexagonal. The edge of a cellular imprint is almost always outlined by sharp furrows that forms a net– or mesh–like pattern resembling a fishing net. The surface area delimited by the furrows or meshes is called a “sculpticell” (Allen and Ball, 1980). A sculpticell surface may be flat, concave or pit–like (Fig. A3.13), convex, scale–like (i.e., surface is raised along the posterior or apical edge) (Fig. A3.14), or even seta–like. Each sculpticell is normally completely outlined by meshes but sometimes one or more sculpticells can be fused (Fig. A3.15). Sculpticells can also be stretched laterally (e.g., transverse meshes may be 2-4 times as wide as long), or longitudinally (an uncommon feature).
Microsculpture is best observed at magnifications above 50 times under diffuse light. To reduce glare a translucent piece of plastic (e.g., tracing acetate) should be positioned between the light source and specimen about 20 mm from the specimen. A 13–watt daylight fluorescent light source also gives very good results.
Size is one variable that affects all structures of a specimen, but which normally is not analyzed or discussed in detail. Size range within well sampled siricid species is great. For example, both sexes of S. noctilio may range between 8 and 36 mm and similar size variation is true for many other species studied. One effect of body size is pit size. Because the taxonomically most significant pits are on the head, the size of pits is stated in relation to a nearby reference point, the diameter of the lateral ocellus. Pit density is also affected by specimen size, often being denser in larger than in smaller specimens of a species. Although the shape of the female cornus does not vary with size for most species (e.g., in S. nigricornis, it remains angular in lateral view for all sizes) in S. californicus the edge of the cornus is convex in the largest females, whereas it is straight in medium size females, and angular in small females.
When possible, 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 and the maximum length of the fore wing. Because a limited number of ovipositors were studied for each species, a range in the observed variation (e.g., for the ovipositor: relative size of pits at base and middle, relative height of pits, shape of pits, total number of annuli, annulus numbers between basal and apical sections of sheath, ridge development on apical pits and on ventral surface of lancet on annuli before the teeth annuli). For a few species, distances between pits 1 and 2, 4 and 5, and 9 and 10 of the ovipositor relative to the ovipositor diameter (including lance and lancet) between these pairs of pits is given. Other measurements were recorded as required. Measurements considered useful are given in Tables 1-5 in the “Appendix for statistical data”. 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 each specimen the following is recorded: country, year, state/province, specimen code, and number of base pairs.