著者

安松 京三 永富 昭

出版者

九州大学

雑誌

九州大學農學部學藝雜誌 (ISSN:03686264)

巻号頁・発行日

vol.17, no.2, pp.129-146, 1959-10

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The citrus fruit fly, Dacus tsuneonis Miyake, is a native pest of citrus trees in Japan, found only in the mainland of Kyushu and the Amami-Oshima Islands, and extensive outbreaks have occurred in some commercial citrus areas since 1947 when up to 60 % or more of the fruits were infested. Although the bionomics and morphology of the fly have been well investigated by T. Miyake (1919) and K. Fukai (1949-1953), several most important basic studies which are essential for its control have remained untouched. It was the purpose of the present investigations to fill the gap between the fundamental knowledge on the fly and establishment of satisfactory methods of its control. During the years 1949-1950, adult flies were collected at about weekly intervals from some citrus groves at Tsukumi District, Oita Prefecture, for the purpose of examining the sex-ratio and the rate of development of the eggs in their ovaries. These flies were dissected at given intervals, and the number of mature eggs counted under four categories : Stage I - the ovary is small, the eggs being hardly visible, Stage II - the ovary as a whole is larger, but the eggs being small not fully developed, Stage III - the ovary is very large and some proportions of the eggs are fully developed, Stage IV - almost all the eggs near the oviduct are fully developed. The results were given in Tables 1-7 and Figures 1-6. The ratio of males to females has remained about 1 from the time of emergence to the middle of August. The authors' observations suggest that copulation is of frequent necessity with female flies that are freely ovipositing and probably takes place after depositing each batch of eggs as observed in Rhagoletis completa (A. M. Boyce, 1934). These findings suggest the possibility of the fly control by a male annihilation method ? a trap baited with attractants ? before the male became sexually matured to prevent the female becoming fertile. The emergence dates vary from place to place, but the detailed studies of some authors and the present authors show that the emergence period covers about fifty days from the beginning of June to the middle of July. The length of the preoviposition period of the flies reared under field laboratory conditions was between 17-25 days. The dissection of the female flies revealed that at the end of July the development of the eggs of more than half of the fly population was in the stage IV and the ovaries were fully developed until at the beginning of August. On the basis of these studies the authors could determine the proper timing of chemical applications for the control of the fly, namely, the first application at the beginning of July and the second one at the middle of the same month. Fukai's recommendation on the time of chemical applications (from the end of July to the first decade of August) seems too late to get effective control. Very little has been known about the feeding habits of the flies in nature. In the earlier portion of the biological studies ordinary cane sugar and honey were used as food for the flies. However, the result was not entirely satisfactory, particularly with respect to longevity and fecundity of females. It was the authors' opinion that honeydew dropped by some Aphids, Coccids or Psyllids might be served as natural food for the flies because almost no fruit was available. during the fly season. Nutritional studies of the flies were made in 1950 under natural indoor conditions. Seven different diets were tested, and suggestive data regarding their natural food were obtained (Tables 8-17, Figure 7). The longevity of the flies decreased in the following order : honeydew of Ceroplastes rubens + water > honeydew of Aphis citricidus and C. rubens + water > 100 % honey + red star yeast + water > water alone > 100 % honey + red star yeast > 15 % honey alone > 100 % honey alone > without food. The fact that the flies fed with honeydew lived extremely longer and could produce eggs suggests that honeydew as the diet of adult flies is necessary for health, longevity and egg production. So far as the authors' observations went, Amphorophora lespedezae (on Lespedeza sp.), Aphis citricidus (on Citrus spp.), Ceraphis quercus (on Quercus acutissima), Greenidea kuwanai (on Quercus gilva), Lachnus tropicalis (on Quercus gilva), Toxoptera aurantii (on Eurya japonica) and Ceroplastes rubens (on Citrus spp. and many other plants) were seen in the citrus groves and nearby bushes as sources of honeydew for the flies at Tsukumi District. Certainly there is a good possibility that control of the flies can be successfully achieved by the eradication of such insects which are supplying honeydew in the fruit fly ecosystem. It is well known that in the late forenoon and early afternoon hours in sunny hot summer days the flies are found not within the citrus grove, but outside and along the border of the grove among wild vegetation and the invasion of the flies into the grove occurs in the late aftern000n hours (from about 3:00 p.m.). Comparison of temperatures between a citrus grove and a nearby bush in a ravine at Tsukumi District (Table 18) reveals the striking difference in temperature between the two environments. This phenomenon of the fly movements seems to be aroused by the temperature gradient, and the facts indicates that the oviposition of the flies takes place in the early forenoon and late afternoon hours in hot sunny days. Evidence of the movements of the flies suggests that the insecticidal applications should be made at the time just before the invasion of the flies into the grove and the insecticides are most effective when applied on border wild plants and further on citrus trees of the border area of the grove itself because the damage of the flies are very severe on citrus trees adjacent to the border wild vegetation.本報に於ては, ミカンバエ防除に必要な生態的生物的基礎研究の中で, 従来欠けていた重要問題のみを取扱つた. 1. ミカンバエ発生期間中の雌雄比について研究した結果, 雌雄は共に比較的長命であることが判明した. すなわち, 雌雄はその生存期間中に何回も交尾する必要があることを示すもので, この事実はミカンバエの誘引剤で, 雄のみを誘引するものの発見でも, ミカンバエの駆除には有効であることを示唆する. 2. ミカンバエ雌の卵巣が, 羽化後どの位の日数を経て成熟するかを研究した. その為には卵巣内での卵の成熟程度によつて4つの段階を設けてこれを研究した. それによつて, ミカンバエの卵巣成熟率は7月中旬で既に50%に達することが判明した. なお, ミカンバエの産卵前期間は17日乃至26日であることを確めた. ミカンバエの防除は産卵開始前に行わねばならないので, 薬剤撒布は7月上旬から中旬の終りにかけて実施することが賢明であることが推定された. 3. 従来ミカンバエの食性に就いては未知の分野ばかりであつた. 諸種の食餌について実験を行つた成績と野外に於ける調査から, 柑橘園及びその隣接の山林に棲息するカイガラムシやアブラムシ等の分泌する甘露が, 恐らく唯一の食物資源であることが断定された. すなわち,ミカンバエを誘引して殺すか又はなめさせて殺す毒餌の研究を行う価値のあることとそれら甘露を分泌する昆虫類の防除とが大切であることが明らかにされた. 4. ミカンバエの行動は日中の気温と密接な関係にある. すなわち,盛夏の候の日中の高い気温の時刻にはミカンバエは柑橘園には棲息できず附近の涼しい山林や谷間の茂み等に移動するので, それらのミカンバエの退避所を考慮に入れた防除方針の一つの樹立もできることが推定された.