Fauna of New Zealand 72: Micropterigidae (Insecta: Lepidoptera) - Morphology
Gibbs, G W 2014. Fauna of New Zealand. 72, 127 pages.
(
ISSN 0111-5383 (print),
ISSN 1179-7193 (online)
;
no.
72.
ISBN 978-0-478-34759-3 (print),
ISBN 978-0-478-34760-9 (online)
).
Published 30 Jun 2014
ZooBank: http://zoobank.org/References/D6BC8C34-6D93-4EC7-BCB3-5670B2CFE744
DOI: 10.7931/J2/FNZ.72
Morphology of relevance to systematics
The morphological terminology used here broadly follows Kristensen (2003) whose contributions on basal homoneurous moths have established the understanding on which this investigation is based. Details of the terms used are outlined below.
ADULT MORPHOLOGY
Head. (Fig. 30–33) Variation in head capsule shape and dominance of the compound eyes in Lepidoptera is expressed in terms of the interocular index (Davis 1975) (vertical height of eye/distance between eyes). Larger eyes (index >0.8) have been interpreted as adaptations for nocturnal activity (Kristensen 2003). Within the New Zealand Micropterigidae, the vertex region maybe high and domed as in some Sabatinca species (e.g., Fig. 31), or relatively low as in Zealandopterix (Fig. 33). This is reflected in the supraocular index (Kristensen & Neilsen 1979) (height above eyes/overall height vertex to gena). A high index (>0.4) is possibly related to the attachment area needed on the supraocular part of the cranium for musculature which operates in the pharate adult of dectious pupae with hypertrophied mandibles (Kristensen 2003). All micropterigids have pupal mandibles but it is not known whether their relative sizes are correlated with this index. Ocelli are present in all known Micropterigidae except Aureopterix (Australia, New Caledonia) but their position with respect to the compound eyes can vary (see contrast Fig. 31 vs Fig. 33).
The sabatincoid lineage is characterised by the exceptionally hairy head and thorax, a feature of all micropterigids but reaching its zenith in the New Zealand and New Caledonian faunas (Fig. 4, 50). On the head these long piliform scales arise from five clearly defined and slightly domed areas of the head capsule—frontal, supra-antennal, sub-ocellar, post-ocellar, and on the vertex. The area between ocellus and compound eye remains as naked, microtrichiated cuticle, hence non-reflective (clearly visible in Fig. 50 above the compound eye). Similar tufts of scales also arise from the scape and pedicel of the antennae (see Fig. 38, 50) and, characteristically in Sabatinca species, the tuft arising from the pedicel extends along the antenna for several flagellomeres. Characteristic also are the tufts of long piliform scales arising from the tegulae and mesoscutum of the thorax (Fig, 54). Their colour varies and may be diagnostic.
The antennae provide many taxonomic characters but, unfortunately, can be easily damaged. Their colour and black banding patterns provide an aid to identification. Length may be important, but more so is the number of flagellomeres which in New Zealand species range from 21 to 44, normally fewer in females than males; and their shape which varies from elongate filiform (4× longer than wide, Fig. 42) to submoniliform (1.2× longer than wide, Fig. 45). Moniliform flagellomeres (like a shuttle-cock) do not occur in any New Zealand micropterigids. The form of the ascoid sensilla organs on micropterigid antennae is a very important character for discriminating between lineages within the family, as mentioned above. The scape and pedicel are enlarged in all micropterigids. In the New Zealand Sabatinca taxa the barrel-shaped scape can reach up to 4× the diameter of the first flagellomere (Fig. 38–40) with its dorsal surface indented at mid-length. The pedicel is likewise enlarged to almost the same diameter but is shorter, approximately spherical. Both segments carry dense tufts of extremely long piliform scales. Note that individual variation in numbers of antennal flagellomeres and the precise position of black bands can occur, so that some allowance needs to be made when interpreting the values given in the text.
The maxillary palps are long (1.3–2.0× head width), 5-segmented, elbowed at joints 1 and 3, with 4th segment the longest at 2.3–2.9× 1st segment and sculptured with very fine transverse striae (Fig. 34–37). The terminal (5th) segment is shortest in Zealandopterix (0.6× 1st segment), and inchrysargyra-group species (0.5–0.9× 1st segment), but longer in calliarcha-group(0.8–1.1). These palps are involved with the manipulation of spores and pollen grains during feeding (Fig. 48). The labial palps are very short, usually 2-segmented in Micropterigidae (Kristensen, 1998); but 3-segmented in all New Zealand species except S.demissa and the chrysargyra-group of species. Von Rath’s organ is situated on the distal end of the terminal segment.
Thorax and Wings. The nature of the dorsal scalevestiture of the thorax, especially on the the tegulae and mesothorax, provides a useful character for discriminating between the two genera of New Zealand Micropterigidae. This vesiture comprises both flat lamellar scales and dense erect tufts of long piliform scales. In the sabatincoid species the tufts arise from two discrete areas—the tegulae and the middle of the mesoscutum (Fig. 54). The broad surface of the remainder of the mesoscutum is clothed with reflective lamellar scales, as is the whole area, including tegulae, in Zealandopterix (Fig. 55). The metanotum is essentially naked but for a few long, very thin hairs. Lamellar scales provide colour to the leg segments, usually forming contrasting colour bands around the segments, especially on the tarsus.
Wing maculation in the Sabatinca lineage is exuberant in comparison to Northern Hemisphere and Australian micropterigids, where the groundplan appears to be essentially dark grey, brown or black pigmentation with a metallic sheen, often broken by a number of transverse whitish bands or blotches. On Zealandia, however, this pattern is rare, (found only in Zealandopterix and S. ianthina), most taxa exhibiting an array of colour and pattern that could rival butterflies. Although providing an intriguing challenge to explain in terms of adaptive radiation, the feature is of enormous benefit to the taxonomist for species identification.
Wing venation of Micropterigidae provides no apomorphies at family level (Kristensen, 1984a) and can be equally uninformative for genus-level phylogenetic signals. Despite this, there are variations that correlate with certain phylogenetic relationships or with wing shape and size (Fig. 25–29). In the forewing, all known Southern Hemisphere genera share the forked condition of both Sc and R, except for the eastern Australian Austromartyria, an undescribed western Australian taxon, and the Ecuadorian Squamicornia, where R remains unforked, as in Northern Hemisphere genera. Variations in the apical area of the wing commonly involve the branching pattern of RS3 + RS4 veins (the situation pertaining to most New Zealand species). The common RS3+RS4 stalk, present in the majority of Sabatinca species, can become progressively shorter to the point where in three species the two veins arise separately from the hyaline area surrounding the inter-RS and RS-M crossvein (Fig. 27) (hence described as ‘sessile’). This latter condition is associated with a broadening of the apical area (and was the basis for establishment of Micropardalis by Meyrick 1912a).
In the hindwing, attention has focussed on the condition of the R vein in Sabatinca species (Tillyard 1919, Philpott 1923, Kristensen & Nielsen 1982, Huang et al. 2010, Gibbs & Kristensen 2011). Four basic patterns of hindwing R vein topology are evident in southern micropterigids— 1: R is wholly separate from Sc in the basal region and remains separate throughout (Austromartyria, Hypomartyria but no New Zealand taxa); or 2: R is separate from Sc in the basal region, from its stem at about one quarter, but coalesces with Sc2 over the distal third (as in Fig. 25—the calliarcha-group species). A variation of this pattern occurs in S. chrysargyra and S. aemula where what appears to be the basal stem of R arises from the middle of the wing, immediately before the RS fork, resulting in a very short R vein approaching the appearance of an oblique cross-vein (as in Fig. 28); or 3: R is represented by only a short ‘vestigial spur’ beyond the distal fork of Sc2 (as in Fig. 26, 27) (a condition found in all Sabatinca species examined so far, except calliarcha-group species and the two chrysargyra-group species mentioned above and except species 10 and 18 from New Caledonia); or finally 4: no trace of a separate R vein remains (as in Fig. 29—Zealandopterix, Agrionympha, Aureopterix, Nannopterix, Tasmantrix). The four descriptive categories given above make no attempt to interpret the evolutionary significance of these configurations. That would require analysis beyond the limits of this revision and dependent on a more complete review of presently undescribed southern hemisphere micropterigid taxa. The issue is further complicated by whether the groundplan hindwing Sc vein is interpreted as being forked (as assumed here) or unforked (Huang et al. 2010). It should be noted that in some specimens, especially of S. doroxena and S. aurella, and also Agrionympha species discussed by Gibbs & Kristensen (2011), a doubling of the entire Sc vein stem is clearly evident prior to the fork, thus supporting the contention that this vein is forked in the ancestral state. Although CuA is strongly represented in the hindwing, CuP is indistinct and normally connected to A1 vein by an oblique cross-vein in the incongruella- and calliarcha-group species.
Male abdomen and genitalia. The 5th abdominal sternite typically bears a pair of glandular orifices in both sexes, raised on a short peduncle, each bearing a radial array of long piliform setae. These glands are absent in S. weheka. Although all are of the same general form in New Zealand species, there is considerable variability in size and the pattern of setal insertion (e.g., Fig. 46, 47). Their function is widely considered to be pheromone production, more specifically the production of sex pheromones in females (Djernæs 2011), although the only investigative study done in New Zealand (on S. chalcophanes and S. demissa) could find no evidence of sex pheromones (Kozlov & Zvereva 1999). On the evidence of repetitive observations of aggregations of both sexes at certain optimal feeding sites (e.g., dehiscing fern sporangia, angiosperm flower clusters; see Fig. 53.) the foremost function of the pheromone is more likely to be one of aggregation, with a secondary role as a sex attractant.
In the adults of all Micropterigidae the 8th abdominal spiracle is non-functional. Segment 8 retains the tergite (T8), but in all New Zealand taxa the sternite (S8) remnant has been lost. A pair of thin anterior extensions from the lower part of the anteromedian sulcus, which can be seen in a number of genera, e.g., some Tasmantrix species and many Sabatinca, had previously been interpreted as a remnant of the 8th sternite (Gibbs 2010), but the newly discovered micropterigid fauna of Madagascar has shed doubt on this view. Examples are now known where both the independent S8 remnant and the anteromedian sulcus extension coexist on the same specimen. Moreover, the origin of segment 9 muscles on the anterior extension indicate it is part of segment 9 (N.P. Kristensen, pers. comm.). In the present account, the extension is referred to as an anterior flange of the sulcus. A truly independent S8 sclerite is found in Micropterix, Agrionympha, Aureopterix and two Tasmantrix species, but not in Sabatinca or Zealandopterix.
Segment 9 dominates this region, providing structural support for the post-genital components. Its single large sclerite, the vinculum, is wrapped around the segment (e.g., Fig. 106), massive ventrally and extending anteriorly to telescope into S7 mid-ventrally; but is attenuated in various ways in its dorsal part. The ground-plan form was probably a complete ring sclerite (Kristensen 1984c), a situation found in three New Zealand species (of Sabatinca), in which a broad melanised ‘bridge’ across the mid-dorsal line closes the ring and supports the terminal diaphragm. In all other New Zealand species and in all New Caledonian Sabatinca species, the segment 9 ring is either incomplete dorsally, or is connected dorsally by only a narrow vestige of the bridge. The posterior margin of the vinculum is clearly defined (and more or less vertical) in all taxa discussed here, in contrast to Micropterix and an undescribed genus from Madagascar (Davis et al, in prep.) where vinculum and T10 are synscleritous. The vinculum of the Sabatinca clade is characterised by strong oblique melanisation along the anteromarginal sulcus. Variations within Sabatinca involve reduction and loss of the dorsal bridge. The entire dorsal part of the vinculum is lost in Zealandopterix and the anteromedian sulcus neither thickened nor melanised. The relative size of sclerite 9 is expressed here in terms of the ratio of its mid-ventral length to the same measurement of S6, a sclerite which is not involved in genital modification.
The post-genital complex comprises tergum 10 (T10) and the gonopods, or valvae, which articulate with the posterior margin of segment 9, enclosing what is best described as a genital atrium, where the anus and phallus project from the terminal diaphragm. Tergum 10 is a discrete uni- or bi-lobed component forming the roof of the atrium, sclerotised and bearing numerous setae and scales dorsally but often naked ventrally above the anal cone. T10 can be greatly attenuated in some species of the aurella-subgroup. The anal cone is supported laterally by a pair of ill-defined sclerites, variously referred to as anal cone sclerites (Minet 1985), anal plates (Philpott 1923c), or venter 10 sclerotisation (Kristensen 1984b). The anal cone sclerites usually bear a number of short macrosetae. These sclerites may be attached to the ventral part of T10 or be independent. Because of the difficulty of giving definitive descriptions of them from conventional preparations, they are not considered as useful taxonomic features here, apart from noting the number of macrosetae.
The densely micro-scaled phallocrypt, a flexible sleeve-like collar of the phallus, emerges into the genital atrium through the terminal diaphragm below the anal cone and between the bases of the valvae. Whether the apex of the phallus is clearly visible in genitalic preparations will depend partly on the position of the phallus within the phallocrypt at the time of death—an element of chance—and partly on the optical density of the phallocrypt micro-scales, which varies between species. The latter issue can be overcome by further clearing, but is most effectively tackled by removal of the phallus and then careful teasing away of the phallocrypt sleeve to reveal the distal phallus morphology. This aspect of male genitalic preparation is stressed because the distal phallus provides a wealth of useful taxonomic detail as well as a strong phylogenetic signal. Recent interpretation of phallic morphology in Lepidoptera (Kristensen 2003) has replaced the term aedeagus with ‘distal phallus’ to describe the nature of the phallus in Micropterigidae. Thus, the entire phallus is best described in terms of a phallobase—the anterior portion—and a posterior distal phallus, the junction being the point at which the phallocrypt arises. The gonopore of micropterigids is made conspicuous by a series of melanised radial folds of cuticle (more aptly described as ‘gonopore teeth’) surrounding the aperture. The shape of the gonopore is extremely variable and thus useful for species or species-group diagnosis but it should be noted that the aperture is capable of changing shape in relation to the reproductive activity of the moth at the time of fixation. For example, in a New Caledonian species with a typical heart-shaped gonopore in which the dorsal lip is deeply invaginated, one specimen examined showed the invagination everted so that the gonopore had become almost circular. A pair of lateral ear-like ‘lappets’, associated with the anterolateral margins of the gonopore in many Sabatinca species, can be useful for taxonomic distinctions. This type of lappet is absent in the calliarcha-group of species, their place being taken by a variety of longitudinal keel-like flanges. Reference is sometimes made to a ‘ventral branch or ‘ventral bulb’, which, as the name suggests, projects ventrally beyond the gonopore. It is regarded as an ‘underlying synapomorphy’ of Micropterigidae (Kristensen 1984c) and takes a variety of forms in the New Zealand taxa, but never approaches the elongate projection seen in northern hemisphere Micropterix orEpimartyria (Kristensen 1984b). The ventral bulb is developed into a distinctive keel-like structure in the calliarcha-group species. In New Zealand micropterigid taxa, the overall phallus length relative to the length of segment 6 sternite, can vary from a modest 1.9× (in Zealandopterix) to 10.0× (in S. quadrijuga). The extra length arises from the phallobase component of the phallus extending anteriorly through the abdomen, and becoming looped back on itself once or even twice (see Fig. 196). Another feature of the phallobase in the Sabatinca lineage is enlargement of the bulbus ejaculatorius, providing attachment for a mass of muscle fibres that constitute the ejaculatory pumping device (Kristensen 1984b); the anterior diameter may expand to 9× that of the narrowest region (e.g., Fig. 156). The anterior aperture is markedly oblique in the majority of sabatincoid taxa but only marginally so in the chrysargyra-group.
The lateral valvae of micropterigids are relatively simple lobes, lacking additional arms and processes, but can terminate in a bilobed apex in some species. Specialised tufts of thickened setae often occur on the inner surface, usually inclined toward the base of the valve, so as to perform a grasping function during copulation, and hence described here as ‘retro-setae’. A small, discrete, mesally-projecting spine may be present near the apex of the valve, defined here as a ‘valve tooth’ (e.g., Fig. 163), bluntly or acutely pointed, robust, and devoid of setal bases—clearly serving a grasping function. The valvae are connected across the mid-ventral area by the arms of the median plate, a thin, horizontal flange-like apodeme in the mid-line which projects forward inside the vinculum, readily visible in profile (lateral) view but, unless well stained, often difficult to see in ventral view.
Female genitalia. The micropterigid segment 8 is normally unmodified in female micropterigids apart from the loss of its functional spiracle, but in the Sabatinca lineage segment 8 can become conspicuously modified and specialised. In chrysargyra-group species this specialisation is minimal and involves a modification to sternite 8 (S8) in five species, where an internal thickened, stain-absorbant transverse rib runs across the mid-ventral line and, in its extreme form, can reach to the lateral margins of the sternite (Fig. 228). A trace of this rib is present along the anterior margin of S8 in the remaining two species of this group. The presence of this rib is marked externally in unstained specimens by a band of de-melanised cuticle. Within the incongruella-group the two New Zealand species are unmodified, whereas New Caledonian species in this group can be highly specialised in the pleural region of this segment (Gibbs & Lees 2014). The calliarcha-group exhibits a wide variety of modifications to segment 8 which, in its extreme, may result in a complex sclerotised pleural pocket (heighwayi, weheka) (Fig. 215), and/or the presence of a thickened melanised strip along the anterior margin, associated with a patch of dense, often specialised, microtrichia (all species in this group).
The female segment 9 exhibits contrasting states in the two micropterigid lineages in New Zealand. A broad ring sclerite occurs in the Sabatinca-clade, occasionally eroded along the mid-dorsal line, but in Zealandopterix there is no sclerite, the entire segment is soft and membraneous, highly extensile, with only a single row of setae around the circumference in the position equivalent to the posterior edge of the sclerite (Fig. 208). Some distinctive specialisations have developed on the 9th sclerite in three species of the calliarcha-group and in two of the chalcophanes-subgroup species.
Segment 10 is retracted into segment 9 in repose and capable of varying degrees of extension for oviposition. The densely setose terminal lobes (anal papillae) are supported by a pair of lateral sclerites: in incongruella-group and calliarcha-group species these are elongate, distinctively U-shaped melanised sclerites (Fig. 210); but in chrysargyra-group and Zealandopterix the terminal sclerites are compact ovoid to squarish, typical of micropterigids in general (Fig. 228). Each sclerite consists of an unspecialised proximal zone, melanised, bearing short setae and microtrichia, but usually delimited from a densely setose terminal portion bearing longer, thicker, posteriorly directed setae.
Internally, as in all Micropterigidae, the wall of the genital chamber forms a characteristic cup-like structure, referred to as the genital papilla, at the point where the spermathecal duct enters. Its walls are laminated, folded and stain darkly with chlorazol black, rendering it the most visible feature of female reproductive system preparations. However, some caution is needed when making comparisons because the papilla is labile and can become everted (presumably during insertion of the spermatophore) and highly distorted, so is not of constant morphology. The orientation of the papilla cup varies among species groups and certain Sabatinca species (e.g., lucilia, heighwayi, weheka) incorporate an irregular lobed sclerite into the base of the cup.
Although delicate and the most difficult region of the genitalia to prepare and examine successfully, the spermatheca morphology (Fig. 223) offers consistent characters with strong phylogenetic signal. This elongate, sacular organ is made up of three regions—a short proximal thick-walled, heavily staining ductus, which passes through the lumen of the papilla cup; a dominant, elongate, thin-walled sac, utriculus, often subdivided into several distinct zones; and a shorter narrow distal lagena, which is relatively uniform throughout the family. The utricular sac can be variously modified. A thick-walled ‘valve-like’ structure can occur near the proximal end where the internal duct is constricted. In certain species (mainly calliarcha-group), a radial pattern of micro-bristles is visible lining the constriction, suggestive of a filtering function.There may also be an expanded pouch or, exceptionally, an appendix-like sac in this area. Variations in the form of the main utriculus sac provide diagnostic characters for the subclades of the Sabatinca lineage. For instance, the presence of a distinctive spherical multiloculate organ at its distal extremity, resembling a bunch of grapes, is diagnostic for incongruella- and calliarcha-group species and applies equally to all New Caledonian species so far examined in this genus. In contrast, the chrysargyra-group species lack this feature where the distal section of the utriculus is represented by a long, narrow, convoluted duct. Other minor distinctions are presented in the taxonomy section and serve to emphasise that what might appear to be random variations can often have considerable phylogenetic significance. The utriculus is a simple, undifferentiated tubular organ in Zealandopterix.
The corpus bursae is especially large and bulbous in the Sabatinca clade, lacking signa in all chrysargyra-group species, but armed with four large tri-radiate signa in the other New Zealand species of Sabatinca. The corpus is quite small and without signa in Zealandopterix. Remains of a discrete spermatophore body have been found within the corpus of S. incongruella and S. demissa, and Epimartyria auricrinella (North America)—all species with large triradiate signa .