Damages of agricultural products caused by the Norway rat in Sagi-shima, a delta of Nobeoka City, Miyazaki Prefecture II. Rat control with special reference to the introduction of the Korean weasel as a natural enemy against rats

In Sagi-shima, a delta of Nobeo k a City, Miyazaki Prefecture, an outbreak of the Norway rat, Rattus norvegicus (Berkenhout) occurred in 1957. Basing on the preliminary surveys in February, 1958 (Hiraiwa, Uchida and Hamajima, \u2759) we have immediately started to undertake the plan , consisted of the following three principles to control rats. We visited the delta again on May 12, 1959, and confirmed the successful results of rat control. The summaries and the considerations concerning the introduction of the Korean weasel, a natural enemy against rats, are as follows : 1) As the first trial, applications of poison were carried out with 6.5 kg of Fratol (1% solution of CH2FOOONa) from March 12 to 15, 1958 (Table 1 and Figs. 1 and 2). Damages caused by rat, though under control for a time, again occurred in July of the same year (Fig. 3). 2) As the second trial, the Korean weasels, Mustela sibirica coreana (Domaniewski) (14 ., 9 d) were introduced in the delta during September 17 to October 9, 1958 (Figs. 4 and 9). The rat outbreak, in consequence, fell down rapidly, and all crops grew well (Figs. 5 and 6). 3) The catastrophe of the rat plague create d a new epoch in the delta for improvement of the farming. We hope that the environment will be improved, when land rearrangement, accompanied with cultivating new special crops such as iris and edible podded pea, will be done (Figs. 7 and 8).4) Considering the relation between the number of introduced Korean weasels per km2 and their effect upon rat control in several cases, the introduction of twenty to thirty weasels per km2 shall be necessary to control rats rapidly. So we believe that it is not so difficult technically to suppress rat plague in a small island (Table 2). 5) Judging from the observations on food chain, the Korean weasels would be able to inhabit and breed under the biological balance in the delta. Recently it was told that a farmer found a mother animal with her young. The typhoon 5906 Ellen which attacked southern Kyushu, brought a flood over the delta from Aug. 7 to 9, 1959 for the first time after the introduction of the weasels. Some problems, such as influence of the flood on the weasels and the possibility of drifting of the Norway rats to the delta by the flood would become clear in the near future. In any way, we ought to preserve the Korean weasels by a law or an agreement in Sagi-shima and neighborhood urgently.宮崎県延岡市サギ島に昭和32年(1957)から大発生の様相を呈し,夏作に甚大な被害を与えたドブネズミRattusnorvegicus(Berkenhout)については前報(\u2759)において鼠禍の原因,被害状況,棲息数,食性および繁殖状態など基礎調査の結果を報告した.われわれの目的は基礎調査に基づいて有効な駆除対策を速やかに確立し,現地農協に駆除実施の指針を示して早急に鼠禍を終焉させるにあつた.昭和34年5月12日駆除対策突施後の効果確認のため再び同島を訪れた.さいわい現地の方々の熱心な実行力によつて早急に鼠禍を制圧し,同島営農振興の一契機を画しえたことは喜びにたえない.今回の鼠禍鎮圧に決定的な役割を果したのは導入放飼されたイタチであつた.イタチが鼠に対する有効な天敵であることはすでに知られていたが,今回ほど早急な成果をあげたことは特筆すべきことである.これは同島が狭小な農耕無人島であるというイタチの効果を実証するに最も適した条件を具えた,いわば天然の実験場であつたからでもある.サギ島における鼠禍は終焉後未だ日浅く,残された問題をはらんではいるが,これらの概要について報告するとともにイタチ放飼について若干の考察を試みたい.本文を草するにあたり岡富農業協同組合佐藤改司組合長,河野岩美元参事,豊田裕吉参事および諸資料の蒐集に特別の御援助を頂いた山之内峻技師や現地の方々に厚く御礼申し上げる.イタチの捕獲許可申請については福岡県林務部治山課藤田芳夫技師に,捕獲および輸送は福岡県甘木市泉町松原牛之助氏に負う所大である.両氏の御協力に厚く御礼申し上げる.なお宮崎大学中島茂教授および帯広営林局合田昌義技官に謝意を表する