FNZ 62 - Trechini (Insecta: Coleoptera: Carabidae: Trechinae) - Introduction
Townsend, JI 2010. Trechini (Insecta: Coleoptera: Carabidae: Trechinae). Fauna of New Zealand 62, 101 pages.
(
ISSN 0111-5383 (print),
ISSN 1179-7193 (online)
;
no.
62.
ISBN 978-0-478-34717-9 (print),
ISBN 978-0-478-34716-6 (online)
).
Published 16 Jun 2010
ZooBank: http://zoobank.org/References/0D2B064C-C2E0-41F8-AB9A-BEB2E4B41412
Introduction
Speleologists in New Zealand are very fortunate. Not only are there ‘sporting’ caves that will test their endurance, and caves with beautiful mineral formations, but also there is a very rich cave fauna covering examples of almost all known arthropod groups of troglophiles and troglobites.
Within the ground beetle family Carabidae there are troglobitic forms in the tribes Harpalini, Zolini, and Trechini. This last group is the subject of this volume, together with their epigean relatives.
About half the known species of trechines in New Zealand are cave-dwellers. Collecting New Zealand trechines is often difficult. The cave-dwelling species are often very sparsely distributed in the caves in which they occur and the surface-dwelling species are not easy to find either. The reason for this is that trechines require habitats with very high humidity and are strictly confined to this environment. They live either in deep litter, or along streamsides, or in caves as already mentioned, or sometimes sub-littorally in beach gravel below the high water mark; habitats that usually escape the attention of general collectors.
The cuticle of adult trechines is often pale and thin, even when fully mature. Some cave species lack eyes, and instead have greatly lengthened antennae to assist in negotiation through three dimensional mazes in total darkness. They often have special tarsal structures to help adherence to moist surfaces. A less obvious problem that troglobites have had to overcome is that of water-balance. With almost 100% humidity, the relative humidity in a cave is above the osmotic equilibrium point of their body fluids and they have to secrete excess water (Howarth 1980). They have, of course, become partly pre-adapted to this situation by living in riparian environments.
Insects that are restricted to caves have had an interesting history as they have had to cope with major geological changes to the landscape over the last few million years. Although this subject must remain somewhat speculative, an attempt has been made to piece together the possible movements of some of the New Zealand species as they have avoided high sea levels and other changes to their environment.
New Zealand trechines range in size from only a few millimetres long to about 10 millimetres. They are rarely common; some species are known from only a single specimen, but this may reflect our inability to sample their true habitat, rather than their actual rarity. Like most Carabidae, they are considered to be predatory, and must rely on other small creatures for food. Because of their very specialised habitat, some species, those living in caves for instance, must be capable of existing for extended periods without food. Larvae of only a few species are known.
Conservation status
The endemicity of New Zealand Trechina is noteworthy. We have no genera shared with Australia and the only non-endemic species is Kenodactylus audouini, which is found in South America and islands in the Southern Ocean. All troglobitic species are of very restricted distribution and are totally reliant on the pristine nature of caves being maintained. It is particularly important that sink-holes, once in bush but now on farmland are not used as convenient rubbish disposal sites, and that forestry operations do not cause siltation or other changes to streams feeding karst areas. Epigean species, with one exception, are all associated with riparian habitats, and although they have coped with massive floods in their time, pollution of waterways could be devastating. A species formerly found in a roadside rill at Belfast Creek on State Highway 6 south of Charleston (BR) has not been seen there since re-alignment of the road. It is fortunate that it is also known from cave systems at Bullock Creek near Punakaiki (BR) and the population there is viable. The apparent rarity of some species (one specimen in some cases) is more likely to reflect the difficulty of collecting and the fact that in caves there are many crevices suitable for fauna but impossible to examine.
Methods
Specimens have been borrowed from various museums and private collections. The following acronyms have been used in the text.
AMNZ Auckland Institute and Museum, Auckland, New Zealand.
BMNH The Natural History Museum, London, United Kingdom.
BPBM Bernice P. Bishop Museum, Honolulu, Hawaii.
CMNZ Canterbury Museum, Christchurch, New Zealand.
ITNZ J. I. Townsend private collection, Levin, New Zealand.
JNNZ J. T. Nunn private collection, Dunedin, New Zealand.
LUNZ Entomology Research Museum, Lincoln University, Lincoln, New Zealand.
MONZ Museum of New Zealand Te Papa Tongarewa, Wellington, New Zealand.
NZAC New Zealand Arthropod Collection, Landcare Research, Auckland, New Zealand.
OMNZ Otago Museum, Dunedin, New Zealand.
The different lineages of New Zealand Trechini are dealt with alphabetically, and within each lineage the arrangement of genera and species follow the order of occurrence in the keys.
Additional relevant information, geological setting, associated biology, etc., is given after each species under “Remarks”.
Measurements of length are taken from the tip of the mandibles to the apex of the elytra, or if elytra are abbreviated, to the tip of the last abdominal tergite. Lengths have been measured using a Leitz micrometer eye-piece and converting the scale to millimetres. The scale bar used in the illustrations is 1 mm unless stated otherwise.
Drawings have been made using a graticule eye-piece and squared paper, or a camera-lucida, or (more recently) using a Nikon digital camera attached to the microscope, copying from a print and adding details of setae, etc.
The two-letter area codes follow Crosby et al. (1976, 1998). Detailed coordinates of caves where these species occur have not been given in this publication because of conservation concerns.
GLOSSARY
abdominal ventrites — segments of the underside of the abdomen
aedeagus — tubular mid lobe of male genitalia
ambulatory setae — pairs of setae situated ventrally on the abdomen
antennomere — antennal segment
apophysis — lamellate or hair-like structure beneath tarsal segment
basal pore — see scutellar pore
cervical groove — depression around neck as a continuation of ocular groove
clypeus — portion of the head between the antennae immediately behind the labrum
cordate — heart-shaped
coxal cavity — area from which legs articulate
disc — central region of pronotum
elytra — chitinous wing-covers of abdomen
emarginate — inwardly curved
epimeron — small sclerite near coxal cavities
flagellum — segments of anetennae beyond scape
fovea — a depression
frons — portion of head forward of eyes
frontal furrows or ocular grooves — longitudinal grooves on head between eyes
genae — swollen portion of underside of head behind eyes
glossa or ligule— tongue-like process on underside of mouthparts
labial palpomeres — tactile segmented portions of the labium
labium — mouthparts seen from the underside of head
labrum — plate-like portion of head in front of clypeus
lamellate hair — a hair that is expanded laterally to form a thin sheet
male genital segment — 9th segment of abdomen that houses genitalia
maxillary palpomere — segment of maxillary palp
mentum — basal portion of mouthparts
mesepimeron — a small plate-like sclerite near the mesocoxal cavity
microsculpture — surface structure of chiton visible at 40× magnification
papillae — small protuberances on the underside of tarsi
pedicel — first antennomere beyond scape
penultimate labial palpomere — 2nd to last segment of labial palps
premolar tooth — an additional tooth at the base of mandibular teeth
pubescent — covered with fine hairs
pronotum — upper surface of prothorax
prosternum — lower surface of prothorax
scape — basal segment of antenna, antennomere 1
scrobes — hollow area on outer face of mandible
scutellar pore — tiny puncture bearing a seta, at the base of the elytra near the scutellum
scutellar striole — a small impressed line sometimes present near the scutellum
stria — an impressed longitudinal line (sometimes broken or consisting of punctures) on elytra, also known as interneur
submentum — area immediately below the mentum
supraorbital setae— prominent setae on the head behind the eyes
tarsomere — segment of tarsus
tempora — head area around the eye
tibia (pro-, meso-, meta-) — segment of fore, mid, and hind legs
troglobite — animal confined to caves and unable to exist above ground
troglophile — animal that can live in caves and also above ground
trogloxene — animal that is not usually found in caves and cannot complete life-cycle there
umbilicate setae — a series of setae arranged near the elytral margin
Generic concept
When faced with a new taxon, there is a choice of either modifying an existing generic description to accommodate it (as has been done for Scototrechus), or of describing it as another genus. Although the number of monotypic genera in this revision may seem excessive, the principle that there have to be differences in a series of significant characters for separation of genera has been followed. There are many monotypic genera of trechines in other parts of the world. The isolated nature of troglobitic and other highly specialised species may account for this.
Trechini
Trechini are small (less than 10 mm), pedunculate carabids in which the mesepimera do not reach the mesocoxal cavities. The most notable character used to define them at the tribal level is the shape of the head. It is relatively large and has very long and deep frontal furrows extending beyond the eyes (when present) and these furrows, in many species curve outwards behind the eyes, so that the eyes are on raised ocular hemispheres (Darlington 1962). They have a series of 8 setae around the margin of each elytron. The mouthparts are also distinctive: the glossa (“languette”) has 2 large median bristles and 2 or 3 smaller setae on the sides (Jeannel 1962), and they have a seta in the scrobes of the mandibles. The terminal and penultimate maxillary palpomeres are glabrous and of normal size, characters that clearly separate them from the Bembidiini, which have the terminal maxillary palpomeres strongly reduced, and the Zolini, in which the penultimate maxillary palpomeres are setose.
The 4th tarsomere usually has paired apophyses, which may protrude forward from the sole as far as the claw, thus underlying the 5th tarsomere. In the New Zealand Trechini these apophyses are always present on at least some tarsi (males and females alike). These structures may be hair-like or lamellate, and no doubt, provide good adhesion to wet surfaces. However, within a population there can be much variation in the length of these apophyses, presumably due to wearing with age. This makes this character of dubious value taxonomically although in broad terms it can certainly be useful. Across the genera, these modifications of the 4th tarsomere vary from nil (i.e., unmodified) on some tarsi, to 2 long setae projecting forward under the 5th tarsomere, to a series of lamellate hairs in the same position, or the structure of the tarsomere itself may be modified into an expanded process from which the specialised hairs arise. They may be present on the 4th tarsomeres of all legs, or the anterior and middle pairs alone and in most cases do not appear to show sexual dimorphism. These characters are most likely derived, reflecting the habitat of marine or cavernicolous species, where such changes would give maximum adhesion to seaweed or smooth wet rocks.