Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua


Gibbs GW, Kristensen NP 2019. Mnesarchaeidae (Insecta: Lepidoptera: Hepialoidea). 78, 105 pages.
( ISSN 1179-7193 (online) ; no. 78. ISBN 978-0-947525-60-6 (print), ISBN 978-0-947525-61-3 (online) ). Published

The endemic New Zealand family Mnesarchaeidae of primitive hepialoid Lepidoptera is revised, with subdivision into two sister genera: Mnesarchaea Meyrick 1885 and Mnesarchella Gibbs, new genus and the addition of seven new species: Mnesarchaea hudsoni Gibbs; and Mnesarchella dugdalei Gibbs, M. falcata Gibbs, M. ngahuru Gibbs, M. philpotti Gibbs, M. stellae Gibbs, M. vulcanica Gibbs; bringing the total fauna to 14 species. Mnesarchaeid taxonomy remained largely unresolved for 130 years due to the look-alike maculation of seven species in the acuta-group. Philpott (in 1920’s) recognised the value of genitalic preparations, but failed to utilise it for taxonomy, apart from resolving the status of acuta Philpott 1929. The present study, based on genitalic dissections of existing museum material plus extensive new field surveys, has revealed five new acuta-group taxa. Adults of all species are described, with colour illustrations from life and of set specimens. Diagnostic genitalic characters are given for males and females.

Although considerably smaller than hepialids, larval morphology is found to be closely similar to the known hepialoids. Pupae lack free mandibles (adecticous) but have moveable abdominal segments (semi-exarate).

Life cycle biology is reviewed. Immature stages depend on the moist ‘periphyton’ layer growing on banks, rocks and logs, where the larvae appear to be polyphagous feeders on fungi, algae, mosses, liverworts, fern sporangia. They spin delicate silken tunnels through which they move to feed and ultimately pupate in a light silken cocoon. Unlike those of hepialids, the eggs are remarkably large and carefully deposited, but like hepialids, possess a soft, pale yellow vitelline membrane that undergoes sclerotisation within 30 hours to become firm and black. Fecundity was determined at a maximum of 32 over a period of four days in captivity. The known phenology implies all species are univoltine with larval development throughout the winter months and the flight season in spring and summer. Diapause has not been recorded. Flight is predominantly diurnal, in dappled sunlight, but occasional specimens have been taken at UV light. Males dominate in collections, with a mean value of 15:1. Females seldom fly but wing area is reduced in only four species; their pigmentation often paler than male. Mnesarchaeids of both sexes display a curious ‘wing-tip-lift’ behaviour after alighting on a surface—the action separates and rejoins the wing tips rhythmically about twice per second.

Mnesarchaeids are distributed throughout New Zealand apart from the far north of North Island and the SE corner of South Island; they are also unknown from Stewart Island. No single species occurs throughout. Of the 14 species, 6 are endemic to North Island, 4 to South Island and 4 are found on both islands. They are unknown from offshore and outlying islands, apart from Hauturu (Little Barrier Island) and Aotea (Great Barrier Island).

Morphological features are described based on dissections, SEM and serial sectioning. Although notably smaller than Hepialidae, morphology of both adult and larval mnesarchaeids supports current molecular phylogenetic views. Mnesarchaeid autapomorphies include wing venation with a single Rs1+2 vein; the lack of any positive wing-coupling mechanism; bilobed sternum A1 with external arms; male genitalia in which pseudoteguminal and valve plates are fused anteriorly to enclose a spacious subgenital crypt; female genitalia with unique elongate dorsal and subgenital plates, synscleritous anteriorly. Distinctive plesiomorphies, evident at coelolepidan level, include discrete mandibles that lack articulation or musculature; a short, coiled, functional proboscis with intrinsic muscle fibres; a primitively 3-segmented maxillary palp; functional salivary glands (as in Lophocoronidae).

Overall the larval morphology is hepialoid but the body form differs, with thoracic segments tapering anteriorly to a more or less prognathous head position associated with a mobile life in silken tunnels. As in Hepialidae, the mouthparts are supported from a rigid oral frame with a narrow ‘lateral slit’ at the antennal socket; they also share a specialised ‘microtrichiated field’ sensory area on the prothoracic shield (incorporating D2, SD1, SD2) with certain hepialid genera. The spinneret is extremely long and mobile, associated with a silk-dependent life-style enclosed in temporary silken tunnels.

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