96 THE ARGENTINE ANT. 



first made in fumigating the boxes with hvilrocyanic-acid gas (see 

 pp. 82-83), but these were not successful. Carbon bisulphid was next 

 tried, with perfect success. Delay in obtaining a sufficient supply 

 of bisulphid resulted in delayed treatment of many of the boxes, 

 and doubtless some of the colonies escaped as the weather became 

 warmer in the early part of February. Nevertheless, the number 

 of queens and workers destroyed ranged into the millions. The 

 owT^ier wished to deal the ants the hardest blow possible, so early 

 in the spring he flooded the orchard, drove the remaining ant colo- 

 nies to the boxes, and fumigated these the second time. 



The results of this work were eminently satisfactory. The orchard 

 was first infested by the ants in 1909. In 1910 they reached enor- 

 mous numbers; chaff and purple scales increased until the trees were 

 almost encrusted, and many of the trees showed signs of failing. 

 The foliage began to turn yellow, and the crop of 1910 fell off 

 severely, in spite of the flooding that was done by the owner in the 

 spring of 1910. During the summer of 1911, following the use of 

 the trap boxes, the orchard improved remarkably, and the crop was 

 up to the original production. It was found that when the boxes 

 w^ere left in the orchard ant colonies took up their abotle therein 

 during the summer months; for this reason these boxes were fumi- 

 gated with bisulphid from time to time. An examination of the 

 orchard in January, 1912, showed that the infestation by the chaff 

 scale had been greatly reduced by diminution of the ants, even 

 though the owner had done no spraying for destruction of the scale 

 insects. The ant infestation showed some increase in the autunm 

 of 1911, but the orchard had returned to its normal healthy condi- 

 tion, and it was evident that a continuation of these methods would 

 insure good crops indefinitely. A view of this orchanl, taken in 

 January, 1912, is shown in Plate XIII. 



One important point came to light in these experiments, and that 

 was the necessity of placing the trap boxes in position early in the 

 autumn so that the vegetation in them would be decaying well at 

 the approach of cool weather in November. With considerable 

 decomposition going on at the time the ants are seeking winter 

 quarters, the warmth of the box becomes very attractive to them. 



The use of arsenicals and other poisons in the infested orange 

 groves was found imjwssible, for the reason that the secretions of 

 scale insects and aphides are preferred by the ants to aU other foods. 



