Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

FNZ 12 - Pompilidae (Insecta: Hymenoptera) - Morphology

Harris, AC 1987. Pompilidae (Insecta: Hymenoptera). Fauna of New Zealand 12, 160 pages.
( ISSN 0111-5383 (print), ; no. 12. ISBN 0-477-02501-3 (print), ). Published 13 Nov 1987


ADULT. Salman (1929) provided a general discussion of the external morphology of an adult pompilid. A number of his interpretations are incorrect, and most later taxonomic studies have used additional terms, with the result that for many structures there has been a considerable proliferation of names. For these reasons the morphological features used here are discussed in some detail, and a list of synonyms in current use for the male genitalia is given.

Because sexual dimorphism is pronounced, many characters of taxonomic importance in females are not present on males, and vice versa.

Head (Figures 3 and 4). Many taxonomically important characters are found on the head. The mandibles have either one or two teeth on the inner margin, conditions termed "unidentate" and "bidentate" by Evans (1950), who - unlike other workers (e.g., Townes 1957) - does not consider the apex to be a tooth. Both the clypeus and the labrum are variable, and are useful taxonomically: for instance, a ratio derived by dividing the length of the clypeus by its width is used at the species level. The eyes, ocelli, frons, and vertex provide useful characters, many expressed in the form of ratios. The ratio POL:OOL is widely used, POL (post-ocellar line) representing the distance of the posterior ocelli from one another; this is divided into OOL (ocello-ocular line), the distance of one posterior ocellus from the nearest point of the compound eye. Evans (1950) measures as well the distance between the compound eyes at three places: the upper interocular distance (UID); the middle interocular distance (MID), which is the distance between the eyes at their greatest emargination; and the lower interocular distance (LID), between the eyes at their point of closest convergence below. The maximum breadth of the head is termed the transfacial distance (TFD), and the height from clypeus to vertex is the facial distance (FD). The former divided into the latter gives another ratio (Figure 3).

The malar space, here regarded as the shortest distance between the lowest part of the compound eye and the mandible, is often useful to distinguish between closely related species. (I have followed Evans - e.g., 1950, 1973 - in dividing the malar space measurement into the length of the second antennal segment. This ratio is no less reliable than that obtained by dividing the malar space into the width of the jaw at its base. In 1974 it was my wish that the descriptions of New Zealand Pompilidae should be readily comparable with those of Evans, who has already described many of the Pompilidae of the Southern Hemisphere.)

The labium and maxilla (Figure 4) have characters useful at the specific and subgeneric level, such as the relative length of maxillary palp segments and the development of the premental bristles.

Male antennae have 13 segments, whereas female antennae have 12. A useful characteristic of specimens in collections is that the antennae of males are gently arched but those of females are more tightly curled.

Thorax. The transverse collar is separated from the rest of the pronotum by a sulcus, the streptaulus. The pronotal lobe is close to the tegulae. Ventrally the large propleuron faces the tempora, and the prosternum - situated between the coxae - is very reduced.

The mesothorax consists of a mesoscutum ("Mesonotum" of Evans 1950) and a posterior scutellum with a flat or rounded discoidal area and declivous sides. Anteriorly the prescutal sulci are minute or absent. Parapsidal sulci extend from the front half-way on either side of the mesoscutum, the area lateral to them being termed the parapsides. (In Epipompilus insularis they extend the full length of the mesopleuron.) A groove partially separates the mesepimeral and mesepisternal parts of the mesopleuron. The large mesopleura meet mid-ventrally, the mesosternum having been eliminated.

The metathorax has a raised metanotum and a depressed metapostnotum, the latter continuous with the metapleura.

The terminology for the thorax used here is illustrated in Figures 5 and 7 (Priocnemis (Trichocurgus) conformis - Pepsinae) and Figures 6 and 8 (Epipompilus insularis - Pompilinae).

Thorax plus propodeum. Students of aculeate Hymenoptera usually consider the first abdominal segment in conjunction with the thorax. Thus, Haupt (1938) proposed the term holmus for thorax plus propodeum in Dryinidae, and Michener (1944) proposed the equivalent term mesosoma in bees. Alitrunk is often used for this region, especially in ants (e.g., by Bolton 1973), and truncus is sometimes used as well (e.g., by Brown & Kempf 1969). In descriptions earlier than 1914 the entire region is usually termed thorax. Mesosoma is most widely used today, and has been adopted here.

Wings. In Hymenoptera the wing venation is more removed from the generalised type than in any other order of insects. It is possibly for this reason that contemporary pompilid systematists use a varied terminology for wing and cell morphology. Many workers (e.g., Townes 1957) use the system of Rohwer &. Gahan (1916), which is a modification of the Jurine system constructed over a hundred years ago. Though simple, it makes no attempt to homologise the venation with that of other insects.

Some European workers use a system devised especially for the Pompilidae by Haupt (1962). It differs from most others mainly in that the cell is always named according to the vein directly above it.

Ross (1936) advanced a system based on the research of workers in insect phylogeny, particularly on critical comparisons between the wings of Hymenoptera and Mecoptera. (Modern entomologists consider the Hymenoptera to have an ancient mecopteran origin, and to be the most primitive of the panorpoid group - e.g., Malyshev 1966.) Ross's system has been widely used, for instance by Evans (1950), Lanham (1951), Michener (1944), Richards (1956), Riegel (1949), and Riek (1970). Because it is arguably the most valid of the existing systems, and is "the most successful attempt to establish a universally applicable system" (Richards 1956), I have used it here as modified by Richards's interpretation. Its terminology is shown in Figures 9 and 10.

Legs. The legs are unusually long. Females often have a dorsal comb-row of teeth or tubercles on the hind tibia. The presence or absence of such teeth or tubercles, as well as the shape of the teeth, is of great importance for distinguishing between the New Zealand species. Legs of females may be smooth, or covered with spines and setae. The shape and position of the single tooth on the tarsal claw and the numerous setulae on the pulvillar pad of the tarsus are used taxonomically.

Metasoma. The remaining abdominal segments are variously termed the abdomen, gaster, or metasoma. The dorsal and ventral plates of each segment (tergum, sternum) are termed tergite and sternite by some authors. The male metasoma consists of seven visible segments. The sixth is emarginate posteriorly, where it bears a pair of small processes on either side. The seventh apparent sternum - morphologically the ninth - forms the subgenital plate (Figure 11) and closes the genital chamber. It is taxonomically very useful at the species level. Across its basal part and entirely within the abdomen lie the basal sclerites, which constitute the true eighth segment.

Male genitalia: structure and synonymy. The male genitalia have proved to be very useful, both for distinguishing between the New Zealand species and as indicators of interspecific relationships. The external genitalia are attached to the hind margin of the ninth segment, and share a common plan with those of most hymenopteran groups. However, the parts are known by an extraordinary number of different names. Those of the early workers are partly listed in Boulangé's (1924) work on the Symphyta. Snodgrass (1941) devised a terminology which has been widely used because it provides the only survey of the structures in all families. However, like most workers who have studied the development of the male genitalia, Snodgrass denies that they include any abdominal appendages, claiming that the parts developed from the primordial penis by secondary sclerotisation in the wall. Conversely, studies based on the comparative anatomy of genitalia of different orders conclude that the parts arose from abdominal appendages, and that only the inner part corresponds to the aedeagus - e.g., Michener (1944a, b), Peck (1937), Smith (1970). The fact that the controversy has yet to be resolved probably accounts for the continued use of a great many terms. Because taxonomists working on Pompilidae over the past two decades have used up to eight different terms for the same structure, I have included a list of synonyms (p. 12). For this study I have used the terminology of Evans (1950), which is based on that of Snodgrass (1941), with minor modifications.

STRUCTURE (Figure 12). The basalmost part of the genitalia consists of a short, hollow cylinder, the basal ring. Beyond this the elongate, median aedeagus is attached to the phallobase by a pair of basal apodemes. On either side of the aedeagus are the parapenial lobes, which are always devoid of setae. External to those structures are the volsellae, of which the distal, elongate digitus volsellaris is very variable between species, both in general shape and in the number and type of sensillae it bears. Its expanded proximal part often bears setae. The outermost appendages are the parameres. These frequently have a raised, heavily pigmented area near the base. I have followed Evans (1950) in terming this area the squama, although Townes (1957) uses this term for the entire paramere. A pair of laminae volsellares lie ventrally between the basal plates, and are produced into one or two sclerotised spines, the basal hooklets, which project towards the aedeagus.

SYNONYMY. The term used in this study is given in bold type, followed by its synonyms in normal type.

  • aedeagus (e.g., Evans 1950)
    • aedoeagus (e.g., Priesner 1965, 1966)
    • penis (e.g., Haupt 1962, Arnold 1950, 1951)
    • spatha (e.g., Wolf 1960, Smith in Tuxen 1970)
    • valve peniala (e.g., Scobiola 1963)
    • penis valve (e.g., Richards 1956)
    • lamina aedeagales (e.g., Ford & Forbes 1980)
  • parapenial lobes (e.g., Evans 1950, Richards 1966, Townes 1957, Smith 1970)
    • lobi parapeniales (e.g., Priesner 1965, 1966)
    • forcipes intermediae (e.g., Haupt 1962)
    • sagitta (e.g., Wolf 1960)
    • lobe dorsal (e.g., Scobiola 1963)
    • inner or dorsal arm of the stipes (e.g., Arnold 1950, 1951)
  • digitus volsellaris (e.g., Evans 1950)
    • parameres interiores (e.g., Priesner 1965-66)
    • forcipes exteriores (e.g., Haupt 1962)
    • volsella (e.g., Wolf 1960)
    • digitus (e.g., Richards 1956)
    • inner paramere (e.g., Arnold 1950, 1951)
    • volselle (e.g., Scobiola 1963)
  • parameres (e.g., Evans 1950, Richards 1956)
    • squama (e.g., Townes 1957)
    • parameres exteriores (e.g., Priesner 1965 - 66)
    • Gonopoden des 9 Segmentes (e.g., Haupt 1962)
    • stipes (e.g., Wolf 1960)
    • outer or central arm of the stipes (e.g., Arnold 1950, 1951)
    • gonostyle (e.g., Scobiola 1963, Smith 1970)
  • basal hooklets (e.g., Evans 1950)
    • lamina volsellaris (e.g., Richards 1956)
  • cardo (e.g., Evans 1950)
    • gonobase (e.g., Scobiola 1963, Smith 1970)
    • basal ring (e.g., Snodgrass 1941, Richards 1956)
    • lamina annularis (e.g., Forbes & Hagopian 1965)
    • gonocardo (e.g., Priesner 1965 - 66)
  • basis volsellaris (e.g., Evans 1950)
  • gonocoxite (e.g., Scobiola 1963)
    • basis paramere (e.g., Richards 1956)
    • lamina parameralis (e.g., Forbes & Hagopian 1965)

FINAL-INSTAR LARVA. Evans (1959b) described the general characteristics of final-instar pompilid larvae. The following account is given in order to clarify the terminology used here.

Body. The body is white, almost fusiform, somewhat flattened ventrally, with segmental pleural lobes, and on each segment except the ultimate one is a crease dividing the dorsum into a pair of annulets. The integument bears setae of varying size on the dorsum and pleura, and sometimes bears minute spicules, especially on the venter.

Ten pairs of spiracles are present; the second pair are much reduced. All are complex in structure (Figures 76 and 77).

The primary tracheal opening lies between the bowl-shaped atrium and the sub-atrium, which is often thrown into a large number of tubercles and extends proximally to a constriction in the trachea. Internally the walls of the atrium are lined with small ridges, many of which bear minute, blunt spines. The basal region of the atrium surrounding the primary tracheal opening is termed the collar, and atrial ridges on this part frequently bear larger collar spines. Spines are often borne by the internal walls of the distal part of the sub-atrium as well. The walls of the atrium protrude slightly above the general body surface to form a rim, from which a very narrow, transparent annulus, the peritreme, slightly constricts the atrial opening.

Head (Figure 78). The head is broader than it is high, giving it a subcircular outline in anterior view. The epistomal suture is very indistinct, and the coronal suture appears to be absent. To the front of the head capsule, on either side, lie a pair of pigmented lines, the parietal bands (Michener 1953, Evans 1959b) or "ocular lines" (Short 1953). A short antennal papilla tipped by three sensory cones arises from each unsclerotised, almost circular antennal orbit. The anterior tentorial arms are visible as thick, pigmented lines on either side of the clypeus, and are continuous with thickenings of the integument above each mandibular base, the pleurostomal thickenings. These latter are continuous with the hypostomal thickenings, which extend back from the posterior articulation of the mandible to the posterior tentorial arms. Head setae vary greatly in length and distribution.

Mouthparts. The labrum has two large lateral lobes and a smaller median lobe, and on the disc bears a marginal row of prominent sensory cones, a transverse band of setae, and non-setigerous punctures. The undersurface of the labrum, termed the epipharynx, is spinulose. The mandibles are strong, not more than twice as long as their maximum width, and heavily sclerotised apically; they have one or two setae, and usually bear three teeth. The maxillae (Figure 79) are setose and bear spicules on their lacinial areas, which extend towards the middle. Anteriorly are borne a pair of blunt, papillose projections of roughly the same size, the inner ones being the galeae and the outer ones the maxillary palpi. The labium comprises a large postmentum and a smaller prementum. The latter bears the spinneret (or silk press), and lateral to it the labial palpi. Characteristic groups of setae on either side of the spinnerets are termed spinneret setae. The following ratios are used in the descriptions:

HW/HH head width divided by head height (the latter measured without the labrum, because this is extensible);
ML/MW mandibular length divided by its maximum width;
LS/OD length of longest head setae divided by maximum diameter of antennal orbit.

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