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Research article
Description of the reduced mouth parts of Coleophora micronotella Toll (Lepidoptera, Coleophoridae), with a new synonym
expand article infoBernard Landry, Giorgio Baldizzone
† Muséum d histoire naturelle de Genève, Geneve, Switzerland
‡ via Manzoni 24, Asti, Italy
Open Access

Abstract

The reduced mouth parts of Coleophora micronotella Toll (Coleophoridae) are described and illustrated. The proboscis is lacking, but rudimentary maxillary and labial palpi are present. The mouth parts of C. micronotella are compared with those of other species of Coleophora, including some others with reduced mouth parts, and their possible adaptive value is discussed. Ramidomia Falkovitsh, 2005 and Ramidiomia Falkovitsh, 2005, a misspelling, are synonymized with Coleophora Hübner, 1822.

Introduction

In Glossatan Lepidoptera, which comprise over 99.9% of the species of the order, the mouth parts typically consist of a labrum bearing a pair of lateral pilifers anteriorly, a haustellum (proboscis) formed by the modified galeae of the maxillae and a pair of maxillary palpi medially, and a pair of labial palpi posteriorly. Mandibles are fully formed only in the non-glossatan Micropterigidae and Heterobathmiidae. In some scattered groups of species of various families and in some larger groups, such as a good proportion of Lasiocampoidea and Bombycoidea, however, a reduction of the mouth parts can be observed. This phenomenon has not been dealt with comprehensively in the literature and we offer some observations in an attempt to explain it in one small species.

As shown in detail by Căpuşe (1971), the members of Coleophoridae, although generally quite small, usually have well-developed mouth parts, especially in the form of prominent, recurved, tri-segmented labial palpi and a functional haustellum. Some species with reduced mouth parts are nevertheless known, such as C. minipalpella Baldizzone, 1998, described from Andalusia, Spain and known from only four specimens. Here we describe and illustrate the vestigial mouth parts of Coleophora micronotella Toll, 1956, for which there are more specimens available for study.

In the original description, Toll (1956) mentioned the colour of the head and antennae, and indicated that the palps are missing in all of the nine specimens of C. micronotella that he had at hand, but said nothing about the lack of proboscis. Falkovitsh (2005) erected the monotypic genus Ramidomia, here synonymized with Coleophora Hübner, 1822 (along with Ramidiomia Falkovitsh, 2005, a misspelling) to accommodate C. micronotella. Along with Baldizzone et al. (2006) and others, supported by the phylogenetic analysis of Bauer et al. (2012), we find it more coherent to use one large genus Coleophora (1340+ described species) than a classification of Coleophora subdivided in numerous small genera that have been erected without comprehensive phylogenetic inference, as exemplified by Falkovitsh (2005). The latter author noted that C. micronotella has short palpi, with the third segment shorter than the second, but did not mention the lack of proboscis. Subsequent records of the species did not add any more morphological information (Baldizzone 1994; Baldizzone et al. 2006).

Methods

The head of one specimen was mounted on slide in Euparal after maceration in about 15% KOH at 60 °C in an oven for an hour, cleaning in 30% ethanol, staining in Orange G and chlorazol black, and dehydrating in baths of 95% ethanol and isopropanol for one hour each.

The photographs of the scaled head as well as that of the slide-mounted whole head were taken with a Leica MZ APO dissecting scope and AutoMontage, the close-ups of the mouth-parts on slide with a Zeiss microscope and AutoMontage, and the scanning electron micrographs with a Zeiss DSM 940-A scanning electron microscope in the Muséum d’histoire naturelle de Genève (MHNG).

Coleophora micronotella Toll, 1956

Figs 1–4

Material

2 ♂ (one dissected, slide MHNG ENTO 5970), ♀ [Italy] ‘SARDEGNA, Orien. | La Caletta | 2.VIII.81-lux | leg.Baldizzone’; 1 ♂ (head prepared for SEM), same data except ’29.VII.81’; 2 ♂ (one dissected, slide MHNG ENTO 7501), ‘SARDEGNA, Merid. | Porto Botte | 23.VII.81-lux | leg.Baldizzone’, deposited in MHNG. 1 ♂ (dissected, slide MHNG ENTO 7503) [Tunisia] ‘Mauretania | Tunesia-Sud | Oase Tozeur | 28.4.-11.5.1981 | leg. M. u. W. Glaser’, deposited in MHNG. Additional material, undissected: 194 specimens from Sardinia (leg. Baldizzone); 30 from Tunisia (24 from Tozeur, 1921, leg. Dumont; 7 from Tozeur e Gabes, 1980, leg. Glaser); deposited in collection Baldizzone.

Description of head

Frontal aspect with appressed scales, with short, apparent scaled palpi, without proboscis. Ventral edge of fronto-clypeus slightly sinuate. Labrum not apparent. Maxillary palpi unsegmented, very short, with few scale sockets and setae, with apical sensillum styloconicum. Labial palpi slightly longer than maxillary palpi, reaching apices of subgenal apophyses, with two segments visible, apical segment about half as long as basal segment and lacking vom Rath’s organ. With sac-like rounded structure laterally from labial palpi.

Figures 1–4.

Head of Coleophora micronotella Toll. 1. Frontal view. 2. Scanning electron micrograph (fc: fronto-clypeus; lp: labial palp, partly collapsed; mp; maxillary palpus; se: sensillum styloconicum). 3. Ventral view showing labial palpi. 4. Dorsal view showing maxillary palpi.

Notes

The halophilous biotope of La Caletta, where three of the specimens of C. micronotella studied were collected, is about one kilometer away from the Mediterranean, on the sides of a small canal where tamarix (Tamarix sp., Tamaricaceae) grows. The specimens were collected with a black light in a salt marsh where Salicornia (Amaranthaceae) and other halophilous herbaceous plants were growing. Hundreds of specimens came to light, but could not come to rest on the sheet because of the presence of thousands of staphylinid beetles and flies. Falkovitsh (2005) recorded that the larva of C. micronotella feeds as a borer, without making a case, in ‘green branches (assimilating shoots)’ of Halostachys caspica C.A. Mey. and Halocnemum strobilaceum (Pallas) Bieb. (Amaranthaceae).

Described from Tozeur, Tunisia, the species is also found in Italy (mainland, Sardinia, Sicily) and Spain. It has also been reported from Iran (Baldizzone 1994), and Algeria, Kazakhstan, and Tadjikistan (Falkovitsh 2005). However, a specimen from the Iranian series mentioned in Baldizzone (1994) was re-examined and found to represent another, probably undescribed species. Its mouth parts are more developed than in C. micronotella, with the labial palpi about as long as 3/4 the widest diameter of the compound eye, but without apparent proboscis. Also, the male valva differs slightly in the distally larger and more evidently separated sacculus from the basally narrower valvula, and the phallus is narrow, needle-like, instead of spatulate.

Other species of Coleophora with vestigial mouth parts

Coleophora galligena Falkovitsh, 1970, described from Uzbekistan, has vestigial palpi and no proboscis. Coleophora daeva Baldizzone, 1994, C. minipalpella Baldizzone, 1998, and C. zagella Falkovitsh, 1972, respectively described from Iran, Spain, and Mongolia, have short proboscis and palpi. These four species and C. micronotella can be associated with the 8th group of Toll (1953, 1962), based on their simple genitalia, but Toll (1956) only mentioned that C. micronotella is close to C. plurifoliella Chrétien, and never associated this species with any group subsequently. These species are associated with halophilous habitats and deserts and they were not treated by Bauer et al. (2012).

Discussion

The sac-like rounded structures that protrude laterally from the labial palpi in C. micronotella may represent vestigial mandibles. Rudimentary mandibles were found in all species of Coleophora studied by Căpuşe (1971), with variation in shape and size. Căpuşe (1971) noted that the mandibles are usually sclerotized, but he found at least one species in which they were membranous (C. asthenella Constant). Căpuşe (1971) did not study C. micronotella, but for comparison it may be noted that among the 100 species studied he mentioned that the maxillary palpi were missing in one only (C. asthenella). Although it is often difficult to count the number of maxillary palp segments precisely because the limits between segments may be not easily discernible, Căpuşe found that the number of segments varied from one to five, the one-segmented species numbering 20, the 2-segmented 31, and the other cases in lower frequencies. Căpuşe (1971) also found that C. ciconiella Zeller, a species with two maxillary palpomeres, has the apex of the maxillary palpi adorned with a sensillum styloconicum.

The labial palpi in the Lepidoptera groundplan are tri-segmented (Kristensen 2003). This is the condition found in Coleophora, but the overall length of the palpi, length of individual palpomeres, shape of terminal palpomere, and vestiture vary across species. Căpuşe (1971) did not study any species with markedly reduced labial palpi. The lack of vom Rath’s organ is unusual in Coleophoridae and presumed here to be linked with the reduction of the labial palpi.

Regarding the proboscis, Căpuşe (1971) recorded no species in which it is lacking, but a few in which it is slightly shorter than the labial palpi, and membranous. No species with reduced mouth parts were found from the Western Hemisphere (J.-F. Landry, pers. comm. to G. Baldizzone), but several undescribed species from the Afrotropical region have reduced proboscis and palps.

Bauer et al. (2012) presented the first phylogeny of Coleophoridae based on a formal analysis of molecular characters; one hundred and two European species were analysed, but neither C. micronotella, any of the above-mentioned species with reduced mouth parts, nor any species of Toll’s 8th group were included. Nevertheless, two of the species groups recovered, the albella and alticolella groups, have species feeding on Amaranthaceae, with the larvae of the albella group being internal miners in the first larval stages, until they become too large to be fully hidden in the nutritive tissue, after which they build a tubular silk case. This host plant choice and the internal feeding habits may point to an affinity of C. micronotella with the albella group.

Although the reduction or loss of the proboscis occurs in many glossatan lineages (Kristensen 2003: 54), the adaptations related to the absence of a functional proboscis are unclear, and no discussion of this phenomenon was found in the literature. Căpuşe (1971: 23) believed that in species with reduced galeae, hence without a functional proboscis, the reduction is correlated with the digestive tract, without qualifying this correlation.

Several species of Saturniidae have reduced mouth parts and do not feed as adults (Taylor 1957), presumably to place most of the energy resources acquired during the development of the larva into the production of a larger quantity of eggs and/or into the development of a more efficient mate locating mechanism, hence the highly plumose male antennae. A shift in energy resource allocation may be the reason for reduced mouth parts in Coleophora micronotella and others, but it may also be that these species live in habitats where food sources (water, nectar) for adult Lepidoptera with low vagility are too scarce or poisonous, such as with a deleterious salt concentration, for example. The fact that C. micronotella and other species with reduced mouth parts live in halophilous or desert biotopes, and that the larva of C. micronotella is a borer (a strategy to avoid ingesting too much salt and/or to secure enough water, perhaps) lend support to this hypothesis. We believe that this phenomenon is akin to the loss of functional wings in some Lepidoptera species living on small, wind-swept islands (e.g., Davis and Mendel 2013) or the loss of functional eyes in cave-dwelling animals.

Acknowledgements

Yuriy Budashkin, Ole Karsholt, Niels Peder Kristensen, Jean-François Landry, Rodolphe Rougerie, Jukka Tabell, and Hugo van der Wolf replied to our requests for information. Florence Marteau and André Piuz of MHNG respectively assembled the plate and did the scanning electron micrographs. Jean-François Landry and two anonymous referees provided useful comments on the manuscript. We thank them all very much for their work in our favour.

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