埼玉県立自然史博物館研究報告 第７号 (1989)
フトゲツツガムシLeptotrombidium (Leptotrombidium) pallidum
の生態に関する研究6.
野外に設置した飼育容器内で見られたフトゲツツガムシの各発育期の形態,生態的特徴および生活史
高 橋 守
埼玉県立川越高等学校
要 約
つつが虫病の発生した秩父市羊山地区のアカネズミから捕集したフトゲツツガムシLeptotrombidium (Leptotrombidium) pallidumの満腹幼虫を，野外に設置した飼育容器の中に放し，飼育した．飼育・観察期間は1985年11月から1987年12月までであった．
フトゲツツガムシの卵から成虫までの全発育期の形態，生態的特徴および生活史の観察を行ったところ，以下の結果が得られた．
雌は卵を一つ一つバラバラに産む．産卵直後の卵は球状で，卵表面には無数の小孔が認められた．幼虫の脚は3対であるが第二若虫と成虫は4対で，活発に活動し体表面には無数の毛が密生していた．第一若虫と第三若虫はそれぞれ4対の脚鞘を有し，静止していた．
1985年11月に，飼育容器内に放された満腹幼虫は，そのまま越冬し，翌1986年4月に第一若虫，6月初めに第二若虫，6月終りに第三者虫，7月終りに成虫にまで発育した．産卵は8月に行なわれ，9月には卵からのふ化は殆ど終了した．ふ化した未吸着幼虫は翌1987年5月まで生存していた．成虫は産卵後も生存，越冬し，1987年5，6，7月にも産卵した．その卵からのふ化は8月には終了した．ふ化した未吸着幼虫は12月まで生存していた．
未吸着幼虫の個体数は秋期に最も多くなり，年間一峰性の季節的消長を示した．
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Fig. 11. Schematic figure of the life history of chigger mite, Leptotrombidium pallidum
considered to be observed in the field, Chichibu City, Saitama Prefecture.
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Ecological study of Leptotrombidium (Leptotrombidium) pallidum, 6.
Morphological observations and ecological features of each developmental stage of Leptotrombidium (Leptotrombidium) pallidum, and its' life history observed in the containers placed in the field.
Mamoru TAKAHASHI
Kawagoe Senior High School, Kawagoe, Saitama Pref., 350 Japan
Abstract Leptotrombidium (Leptotrombidium) pallidum is one of the most important vectors of Tsutsugamushi disease in Japan.
Author dealt with the morphological observations, ecological features and the seasonal occurrence of each developmental stage on the life history of L. pallidum in the containers. The containers were placed in the miscellaneous trees at Kawagoe City, Saitama Prefecture.
The observations were carried out from November, 1985 to December, 1987.
The developments of L. pallidum in the containers were observed with a stereomicroscope.
52 fully engorged larvae were obtained from Apodemus speciosus captured in the area of Hitsujiyama, Chichibu City. They were reared in the plastic containers placed in the field through the entire life history(Fig. 2).
Results obtained were as follows.
The eggs of L. pallidum were laid singly on the surface of plaster of Paris, not in a cluster. Newly laid egg was sphere in shape, and a great number of small pits were observed on the surface.
Larva was with six legs, but both deutonymph and adult were with eight legs and with numerous plumosa setae on their body surface.
Both protonymph and tritonymph were with eight leg sheaths. Protonymph is the transition stage from engorged larve to deutonymph, and tritonymph is from deutonymph to adult. They are entirely motionless.
The movement of unfed larva was much faster than any other stages' movements. They usually formed a cluster and stayed on the surface of plaster of Paris.
The erlgorged larvae placed in the containers passed the winter as they are, and they developed into protonymphs in April, 1986, into deutonymphs early in June, into tritonymphs in the latter part of June and into adults in the latter part of July.
The oviposition by females were seen in August. The hatching of the un fed larvae almost finished in September, 1986 and some of them lived till May, 1987. After the ovipositions, adult females continued to live arid passed the winter. They oviposited again in May, June and July, 1987. and the hatching of the larvae finished in August, 1987 and continued to live till the end of the year.
The number of unfed larvae in the containers reached to the maximum in autumn and gradually decreased after that.