FNZ 9 - Protura (Insecta) - Life Cycle and Biology
Tuxen, SL 1986. Protura (Insecta). Fauna of New Zealand 9, 52 pages.
(
ISSN 0111-5383 (print),
;
no.
09.
ISBN 0-477-06765-4 (print),
).
Published 24 Feb 1986
ZooBank: http://zoobank.org/References/6B017956-58FF-4405-9795-98BA1D6FE682
Life Cycle and Biology
As already mentioned, Protura are the only insects with anamorphosis, meaning that they add body segments during development. Berlese knew this, but thought that only one segment was added from each stage to the next. In 1949 I proved this to be incorrect, and described the true development. The names I then attached to the different stages may not have been very happily chosen, but they have been used ever since.
Protura hatch as a prelarva (proved without doubt by Bernard (1976)), which probably is immobile. It has only nine abdominal segments and relatively undeveloped mouthparts, and often the thoracic and abdominal legs are poorly developed (Figures 18 - 21). The prelarva develops into a larva I with nine abdominal segments and fully developed mouthparts and legs. From this stage it develops into a larva II with ten abdominal segments (the new stage is often discernible in the cuticle of the preceding one if they are cleared with, e.g., lactic acid or other agents). This develops into a maturus junior (the name given by Womersley) with twelve abdominal segments, often a smaller number of setae, and no external genitalia. From this, finally, develops the adult - though often a preimaginal male stage with incomplete external genitalia intervenes.
Development takes place entirely in the soil or in decaying wood, where Protura may occasionally be found (Tuxen 1931). In my 1931 paper I supposed a relationship between the pH of the soil and the presence of Protura; in acid soils their abundance was far greater than in alkaline ones, where often they could not be found at all. Later papers by other authors have to some degree corroborated this result, but more thorough investigations have now been made. In my papers of 1931 and 1949 I supposed the mineral soil horizons to be more or less free of Protura, but investigations in Brazil have shown that this is not always true. It may be, as Yin (1981) showed, that different genera descend to different depths in the soil, and thus are found most abundantly at different levels. Also, their yearly cycles may be different; in 1949 I found a Danish Eosentomon species that was what I called euryplastic, with young stages all the year round, whereas an acerentomid species was stenoplastic, with a distinct breeding season.
As to the diet of Protura, Sturm (1959) showed that two European species, an Eosentomon and an Acerentomon, were feeding on mycorrhiza on beech. In Brazil I used this experience to help me decide under which trees to look for Protura, but no further investigations have been made.
As to the ecology of New Zealand Protura, nothing can be said. The localities are always given as "moss and litter" under trees and bushes of many species, though often Nothofagus. This may have a connection with mycorrhiza, but may also be a collection artefact reflecting the abundance of this tree genus. Nothing is even stated about the depth range of the samples [Usually shallow. - Editor] or the composition of the soil. A wide field is open to New Zealand soil biologists.