This test was instituted to protect race horses from injury caused by horse flies (Ta banidae) in the race course. Methods for extermination of the mosquito, Stomoxys calcit ranr, and gnats among the bloodsucking insects attacking horses had been firmly establish ed. Against the horse fly, however, no extermination method had been developed as yet. This is because the larva of the horse fly lives in soil for a long time and the adult of it is active in a very wide area. Therefore, it is very difficult to exterminate the horse fly by any insecticide. Recently, traps to catch horse flies have been devised by KITAOKA and by SHINOHARA. So both of them were used in this test. In the trap of Kitaoka's type (Fig. 1), horse flies are invited into the trap owing to the warmth of sun light. In the trap of Shinohara's type (Fig. 2), horse flies are invited into the trap by carbon dioxide gas originated from solid carbon dioxide (or dry ice). Last summer (in 1968), traps of the two types were tested in the Joban Branch of the Equine Health Laboratory, the Utsunomiya Rearing Farm, and the Chukyo Race Course. As a result, the trap of Kitaoka's type was not so efficient under the conditions adopted in this test. The trap of Shinohara's type was relatively effective in catching flies. Even in case of the latter trap, not all the horse flies that had been invited into the umbrella of the trap were collected in to the upper metallic basket. Therefore, it was considered necessary to devise a more efficient trap to collect horse flies. Then, a reformed trap (Fig. 3) to which had been applied sticky ribbons was pre pared after the design of the trap of type of TUGWELL et al. (Fig. 4). The reformed trap was so efficient that 191 horse flies were collected in the Chukyo Race Course for 6 hours. It was proved to be an excellent one useful even under not so very good weather conditions. Such being the case, it is assumed at present that the reformed trap may be most effective to catch horse flies, although it may not be so sufficient as to exterminate these insects.

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