CONTEOL OF ARGENTINE ANT IN CALIFORNIA. 25 



Crystallization. — The sirup prepared with the formula used in 

 orchards A and B commenced to thicken in from two to four weeks 

 after its distribution in the orchard and crystaUization started in 

 from six weeks to two months. Sirup distributed in the dry cold 

 weather of late fall was observed to crystallize in some cases within 

 a month. The sirup proved less attractive to ants as it thickened, 

 and crystallized, sirup was little attended. Although the Barber 

 formula proved very effective against the ants under conditions where 

 heavy feeding followed the initial distribution, and control was really 

 effected during the period of normal stability of the sirup, as was 

 the case in orchards A and B, weather conditions and normal food 

 supply of the ants frequently were such that feeding was slight 

 during the early weeks of distribution. If in such cases the sirup 

 became crystallized within a month or six weeks following the dis- 

 tribution its effectiveness against the ants was greatly reduced. 



The situation is well presented by the comparison of ant control 

 in a 10-acre orchard adjacent to orchard B, at Upland. The orchard 

 consisted of 676 trees, 76 of which were reserved for control by 

 another system. Ant control by the same sirup as used in orchard B 

 was started in the remaining 600 trees, which were largely navel 

 oranges with ant infestation practically identical with that in orchard 

 B. The distribution took place during the first part of November, 

 or fully a month later than in orchard B, and the sirup crystallized 

 within a month after being put out. Although above 99 per cent of 

 the trees in orchard B were free of ants on March 24, 1918. in this 

 latter orchard only 65 per cent were in this condition. The differ- 

 ence in control is attributable to a shorter period of sirup supply. 

 This crystallization of sirup led to experinaents in an effort. to secure 

 a sirup of greater-stability and .possibly more attractive to the" ants. 



* MODIFIED BARBER FORMULA I. 



Observations indicated that sirup which had become diluted by 

 rain entering the container was more stable than the more concen- 

 trated sirup. This led to the use of a modified formula in which the 

 sugar was reduced from 15 pounds to 12 and the honey increased 

 b}^ one-half pound to compensate for the reduced sweetness. Experi- 

 ments with this sirup during 191S proved it to be as attractive to ants 

 as the original formula and its stability was greatly increased, for 

 during the summer it remained without crystallizing for periods up 

 to four months. This sirup was used over a great acreage during 

 1918 with marked success. With the approach of cold weather it 

 was found that this sirup would crystallize, though much more slowh^ 

 than the thicker sirup. 



Unboiled sirup. — An experiment was started on 50 trees in which 

 the modified Barber formula was prepared without boiling, the sugar 



