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, '59) 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.
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