著者

武藤 明

出版者

東京昆蟲學會

雑誌

昆蟲

巻号頁・発行日

vol.28, no.2, pp.97-109, 1960

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Our knowledge of the biology of Tanypteryx pryeri Selys, the sole representative of an archaic family Petaluridae in the Far East, is still very fragmentary. Since 1956 the author has undertaken ecological studies of this species in the hilly region of Kanazawa-city, Ishikawa Prefecture, Central Japan. The present paper outlines the imaginal life of this species and presents some results of the captive-experiments concerning with the relation between sexual behaviour and territory. Tanypteryx pryeri is a low mountain dweller and is known to occur in Honshu and Kyushu. The flight season is usually in May and June in lower localities of Central Japan. Emergence takes place in the early morning, but in a dark room it occurs notwithstanding the time of a day unless the temperature is extremely low. Since about two weeks before the emergence the nymphs prefer to stay outside their burrows in the daytime. They seem to bath warmth during this period. The type of their emergence resembles that of a Gomphid but shows several interesting characteristics. Exuviae are found clinging mainly on the leaf-face of Houttuynia cordata or Equisetum arvense in Kanazawa area. From a marked area (Mitsukoji) a total of 47 ♂♂ 47 ♀♀ adult dragonflies emerged out in 1959 : Whole duration of emergence was 13 days and the day when 50% of the annual population emerged (EM 50) was reached by the 8th day of emergence. Owing to the heterogeneity, emergence of a reared population (36 ♂♂ 48 ♀♀) was less synchronized : EM 50 was at length reached by the 14th day. Teneral insects fly about to and fro on the sunny slopes in the valley and feed on flying small insects. Since the wing muscles are still rather weak, their flight distance is short, their motion rather sluggish, and they prefer to alight on the trunks of trees. Sometimes they move from shaded valley to a sunny hillside even in the evening, but never show crepuscular activity. When matured (two weeks or so) they come to the mating site. A male insect occupies his territory and defends it against intruders. The place where a territory is frequently settled is an area over which females often come flying about, such an area must have ecologically high potential. Territory of this species is an alighting type and the territorial boundary is obscure if compared with a cruising type shown by Aeschnidae. The duration of territory occupation is not long but rather transient, and the tendency to localize to a definite site is not absolutely strong. When a resident leaves his spot it is soon occupied by a new comer or an invader, probably according to the potential of the site, and, through such a shift of the occupant dynamic equilibrium will be maintained. When a female insect comes flying into a territory the male insect immediately pursues her to mate, but if the passer-by was a male insect or different species a persistent pursuit is not made. The connecting of both sexes occurs sometimes on the ground, the couple then flies away in tandem to some adjacent grove. Copulation takes place clinging on a twig of a small tree. The type of copulation belongs to Anisoptera-type, but it resembles more or less to that of Epiophlebia superstes. Under natural conditions male-by-male coupling, or, coupling with other species hardly occurs, but my captive experiments using a string-tied insect facilitated these erronous behaviours by disturbing or modifying the reactions and flight attitude of the captive test-insect. Male insect even seizes a captive which is of different colours, or of different shapes, or of different sizes, but do not react upon motionless decay, even if it were a true Tanypteryx female. Therefore the first chain of their sexual behaviour must be released by the specific movement of the captive. The territory establishment of this species seems to mean a space and time segregation in a habitat originated from the intra-specific reciprocal reaction, and will result in the dispersal of population density in the mating site. After copulation the female insect separates from the male, and proceeds to anoviposition site. In this species the interference by male insect during oviposition have not been observed. Oviposition is performed by a single female into wet soil, mosses and decaying vegetable matters which cover the ground of a boggy slope along hillside road or forest edge. Females have well developed ovipositor, although the ovipositor type is never endophytic. Details of the larval life and other ecological points of this species will be published in my future papers.