FNZ 27 - Antarctoperlinae (Insecta: Plecoptera) - Biology
McLellan, ID 1993. Antarctoperlinae (Insecta: Plecoptera). Fauna of New Zealand 27, 70 pages.
( ISSN 0111-5383 (print), ; no. 27. ISBN 0-477-01644-8 (print), ). Published 18 Feb 1993
There is a sharp division in habitat between the two genera of Antarctoperlinae in New Zealand. Vesicaperla nymphs are terrestrial, living in the cool, humid microclimates afforded by alpine vegetation. My observations (modified from McLellan 1967) on V. substirpes express this in more detail.
This species was found in alpine herbfields and grasslands where the yearly precipitation exceeds 7000 mm. Most nymphs were concealed in decaying vegetation deep in the tussocks of the alpine snowgrass species Chionochloa flavescens and C. pallens, but thirty-five were found in the skeleton of a red deer (Cervus elaphus) in a mixture of decaying vegetation and what remained of the animal after 2 years of weathering.
The gut contents of nymphs, preserved in the field, consisted of tracheophyte material mixed with fungal hyphae and spores, so it appears that the method of feeding is to strip the outer layers of dead plant material bearing the fungus. The deer carcase with its residue of ingested plant material would have provided a rich source of fungus and the humid microclimate favoured by the nymphs.
Nymphs were reared in a glass container partly filled with the decaying vegetation in which they were found, and kept cool. They were sluggish, and remained in the same position for some time, usually with the middle part of the abdomen against the substrate, the hind end raised, and the cerci wide apart. When disturbed, both nymphs and adults would extend their antennae and forelegs forwards and the remaining legs and cerci rearwards. This action, together with their dark and pale dorsal and ventral colour patterns, camouflaged them in the vegetation. If touched, or if the vegetation was moved, they would frequently drop and remain extended or assume a relaxed pose for some time. Adults varied this by scurrying rapidly for cover.
Nymphs were not seen in the water which collected in the bottom of the container, and if put in water would immediately climb out.
In contrast the nymphs of Zelandobius are aquatic, though they will clamber out of the water on occasion. From observations in the lower Buller Gorge (BR - NN) I noticed that two common species preferred different types of watercourse. Z. furcillatus I found only in the Buller River, which carries considerable silt when in flood, whereas Z. confusus was found only in tributary streams like Fuchsia Creek, which is not silty when in flood but is stained a humic brown by the surrounding protective forest.
The spiny nymph of Z. illiesi inhabits another type of stream. Again in the lower Buller Gorge, on the Ohikanui terrace, I found nymphs of this species mainly on decaying fronds of a tree fern (Cyathea smithii Hook.f.) in a small stream flowing through mixed podocarp/Nothofagus forest. The substrate is sand, gravel, and some mud, and the stream frequently disappears under the roots of trees. Rainfall is high (>3000 mm per annum, spread throughout the year), and flooding often occurs, so that much dead vegetation is swept into the stream to lodge against obstructions. David Marx (pers. comm.) states that at Lake Pounui (WA - WN) specimens were found in heavy bush, in a small stream littered with detritus, leaves, and logs. At first glance the spines on this species would seem ideal for detritus to cling to, but the nymphs I have found have not had such material attached to them; however, the spines themselves afford good camouflage.
Another species, Z. pilosus, does use detritus in this way, particularly in its early instars, when the nymph is clothed in long, translucent hairs which in turn are clothed in smaller hairs, giving the animal a shaggy appearance. The hairs trap detritus and make the nymph difficult to see (Death 1990). This is the best studied of the Zelandobius species, so the biological notes in Death (1990) are summarised here. "Nymphs collected in small to medium sized streams in Cass/Porter Heights region of inland Canterbury where they may occur in quite high densities. Although observations were made throughout the year, adults were only found in winter (June-August) when snow may lie for short periods and air temperatures regularly fall below zero. Adults collected from the wild had no particulate material in their guts but fed readily on sugar solution in the laboratory. Nymphs appear to feed predominately on detritus and periphytic algae although animal remains were found in guts of some late instar nymphs. Females collected in the field laid eggs in batches of 45-156 in petri dishes of water. Some batches were stuck in a jelly-like substance to the bottom of the dish in a coherent mass, 1 layer of eggs deep. Other eggs were laid singly. Eggs hatched sy[n]chronously after 6 weeks at 5 degrees C." The adults collected by J.G. Penniket and myself show that emergence of adults is not restricted to the winter.
The method of camouflage used by the nymph (detritus sticking to long, branched hairs) is not unusual in Antarctoperlinae. Illies (1963) describes the same in the nymph of Pelurgoperla personata Illies from southern South America. In Zelandoperlinae the early instars of New Zealand's Acroperla spiniger are very hairy and spiny. Nymphs of Notonemouridae also show this adaptation (Illies 1961, 1975, McLellan 1991).
In many Zelandobius species mites have sometimes been found attached to the proximal abdominal tergites or their intersegmental membranes. These mites are commonly found on most species of stonefly in all families found in New Zealand. The only mite species named from New Zealand stoneflies is Panisopsis wiselyi Womersley, described from larvae attached to adults and nymphs of the wingless terrestrial gripopterygid Apteryoperla monticola Wisely.