The purpose of this investigation was to find an ideal and the most practical method of control of Dacus tsuneonis Miyake, a serious pest of citrus trees in Japan. In the fight against the fruit fly, growers of Oita Prefecture employ two kinds of practices which have been recommended by K. Fukai. The first method is dusting or spraying the citrus trees with such insecticides as BHC (powder 1 %, 50 kg per hectare) or DDT (wettable 0.05%, 3600
per hectare). The second is the clean picking of the infested fruits before dropping. The first application is carried out between July 20 and July 25, the second one between July 27 and August 1 and the third one between August 3 and August 8. As indicated in the authors' previous paper, this is not the proper timing of the chemical applications, and further it should be borne in mind that the applications of DDT or BHC are detrimental to the natural enemies of the other pests occurring in the citrus grove. In establishing any practicable and ideal scheme of control, the following important problems were taken into consideration by the authors. 1. The public health aspect. It is well known that many of the newer synthetic organic chemicals are highly toxic to the warm-blooded animals. Therefore, we must utilize the chemicals as less toxic as possible. 2. The financial aspect. The cost of control must be as lower or cheaper as possible. The measures to be taken must be as simple as possible and therefore adapted to application by unskilled labour under supervision. 3. The question of natural balance or the protection of natural enemies. In many instances, the use of many of the newer synthetic organic chemicals for the control of one pest of a crop has resulted in another pest, which may be normally of little economic importance, assuming epidemic proportions. In the citrus groves, there occur many injurious insects and mites. if the control measure is applied without considering this fact, the outbreak of one or more pests other than the fruit fly must be expected. 4. The development of resistance t o chemicals by the insects. Since the introduction of the newer synthetic organic insecticides in the pest control programmes, the development of resistance has become of great concern to many countries. Therefore, the introduction of such insecticides into the citrus groves must await a fuller knowledge and investigations of the chemicals to be used. From the foregoing considerations it seems important that the study of chemicals for the control of the fruit fly should be concentrated to those of attractants and bait-sprays, although all the newer synthetic organic chemicals have been tested since their appearance. The control studies were treated under two categories, namely, laboratory investigations and field investigations. The laboratory investigations extended from 1951 to 1953, while the field ones began in 1952 and extended through 1956. Nine kinds of attractants (Ammonium phosphate, ammonium diphosphate, ammonium pollard, iso-eugenol, various protein-decomposing products) were tested, but all proved to be ineffective. Six kinds of bait-sprays (tartar emetic, copper carbonate, sodium fluosilicate, lead arsenate (to each of them white sugar and water were added), phrymarol plus ethylalcohol) were tested. Among them, the authors got an outstanding result by the tartar emetic bait-spray. The results were as shown in Tables 1-5. The best formula of the bait-spray was : ? tartar emetic 8 g, white sugar 40 g, and water 1.8 kg. This amount is adequate to apply to the area of 9.9 ares. The residual effect seems to last about two weeks or more. Application of about 0.3 litre of the bait-spray per tree is enough and requires only fifteen minutes with an ordinary knapsack sprayer. The cost of spraying the tartar emetic bait varies considerably, depending upon the size and number of trees in the grove. But the authors' estimates place the cost of spraying about 560 yen (360 yen = 1 dollar) per acre per two applications, not including the cost of labour. This cost seems cheaper than the method of application of the bait-spray including the protein hydrolysate and the phosphatic insecticide (about 720 yen per acre) and much cheaper and safer than the application of DDT or BHC. In 1953 the field experiments were conducted in Hotaku-gun (Plate 2, A and B), Kumamoto Prefecture, using three citrus groves. The results were as shown in Tables 6-7 and Figures 2-4. The field experiments showed that the aplication of the tartar emetic bait-spray was the most effective and promissing method for the control of the fruit fly. On the basis of bath laboratory and field investigations, the authors recommended that tartar emetic bait-sprays for general use in the control campaign in the severely infested citrus areas of Kumamoto Prefecture. The results of three years investigations which were performed in eleven citrus groves were as shown in Tables 8 and 9. The results are especially encouraging since they were obtained in large areas in which there were considerable infestation and damage by the fruit fly. The tartar emetic bait-spray must be applied to a patch of foliage on each tree two times at intervals of about ten days, and special attention should be taken in applying the spray to the citrus trees planted in the border area of the grove which is adjacent to the wild vegetation or to the wild vegetation close to the citrus grove. The superiority of the tartar emetic bait-spray method for the control of the fruit fly to the other methods of control is that the spray is entirely harmless to the warm-blooded animals (1), its cost is by far the cheapest and the labour for its application is exceedingly minimized (2), the adverse effect of the spray on natural enemies of the other pests in the citrus groves almost neglizible (3), and finally application would prevent the development of resistance to such insecticides as many of the newer synthetic organic chemicals by the other injurious insects or mites they formerly controlled (4). Since 1954, the tartar emetic bait-spray method has been safely and satisfactorily applied by the growers to many citrus groves in Kumamoto Prefecture.