CONTROL OF ARGEXTINE ANT IX CALIFORNIA. 37 



ber 15 had spread to 41. By the middle of December this ant had 

 estabhshed colonies throughout the orchard, with the exception of 

 the corner where the Argentine species still maintained a foothold. 

 Several instances of like incursions, but in lesser degree, occurred in 

 orchards at Upland in 1918 and at Alhambra in 1919. 



Relation of Breeding to Control. 



The most rapid and conspicuous increase in numbers of ants is 

 during the months of July, August, and September, and this is ac- 

 counted for by the high mean temperatures prevailing during that 

 period and the abundance of available food. High temperatures 

 stimulate the queen to maximum egg production, and the life cycle 

 of workers from egg to maturity under these most favorable weather 

 conditions approaches four to five weeks, instead of two to four 

 months, as during the coldest weather. Since the Argentine ant has 

 been observed to slacken activity at temperatures below 60° F., it is 

 apparent that during the spring and autumn not only does the egg 

 production become greatly reduced, but the period of development 

 is lengthened. Therefore, poison distributed during the spring and 

 autumn should prove most effective. 



During the hot summer months when all stages are present and the 

 development is so swift the rapid destruction of all workers present 

 at the time of sirup distribution would not clean up the infestation 

 because additional workers would be daily emerging from the pupse 

 and these could care for the undeveloped larvie. Eradication of the 

 young during the summer by poisoning of workers is less Hkely at 

 this time than during the period of slow development. 



CONTROL ON MARGINAL TREES. 



Ant eradication has been most difficult on the outside rows of or- 

 chards, particularly so when bordered by ditches or strips of uncul- 

 tivated land. In clean-cultivated orchards, as stated elsewhere in 

 this bulletin, there is little movement between trees, yet the marginal 

 rows are commonly attended by ants breeding in the strips of border- 

 ing ground. If this adjacent territory is heavily colonized by ants, 

 the latter will be attracted by sirup on these trees. The greatest 

 difficulty has been experienced at times in eradicating ants from these 

 trees, and ants have been eradicated from entire large orchards with 

 the exception of outside trees. The difference in rapidity of eradica- 

 tion between the marginal two rows of trees and the rest of a lO-acre 

 orchard by the sirup method is shown in figure 17. Orchards from 

 which ants have been entirely eradicated one year have been kno^vn 

 to have the outside two to three rows reinfested the following year 

 from adjacent ant-sustaining territory. As a matter of precaution it 

 is sometimes advisable to keep containers of sirup on the outside row 



