34 BULLETIN 965, IT. S. DEPARTMENT OF AGRICULTURE. 
was put out on 46 trees in |-pound paraffined bags and on 46 trees 
in 2-ounce paraffined spice tins. Frequent inspections were made of 
the feeding habits and careful attention paid to any apparent prefer- 
ence for either type of container. The experiment was conducted 
for two months and percentages figured showing the relative feeding 
habits. An average of 63 per cent of the bags were attended during 
the period, and an average of 62 per cent of the cans were fed upon. 
The ants showed no apparent preference for one type of container 
over the other. It has been observed that evaporation is more rapid 
in the bags than in the cans, hastening thickening of the sirup. 
FACTORS INFLUENCING CONTROL. 
The control of the Argentine ant under California conditions is very 
variable. In some cases control has been effected within one to two 
months and occasionally eradication within a like period. In others 
not even a noticeble reduction of ants has been accomplished within 
a much longer period. Inspection of containers in certain orchards 
has shown an occasional ant to feed for several weeks after distribu- 
tion, while in other cases containers would be swarming with ants 
within a few hours after the sirup was placed within reach. As 
a general rule, however, the feeding is heaviest for the first few days 
when the sirup is fresh; after this the attractiveness is somewhat 
reduced. 
Weather. 
The weather, especially the temperature, appears to influence 
feeding greatly. During the hot summer months an arsenical sirup 
is less attractive than at any other time of the year, and control is 
slow, frequently unsatisfactory. The ants at this period are ex- 
ceedingly active, and heavy streams have been known to pass up and 
down the trunk for weeks at a time, in some cases even right up against 
the container, without being influenced in the least by the proximity of 
the sirup. This extreme indifference to sirup is the exception rather 
than the rule. The maximum temperature at which ants actually 
slacken or stop activity has never been noted, but the senior writer 
has observed ants moving freely along the tree trunks at a tempera- 
ture of 117° F., a degree of heat that proved destructive to many 
Diptera and Neuroptera. The writers have observed that the move- 
ment of ants becomes sluggish as the temperature of 50° F. is ap- 
proached, and it is during these periods of low temperature that the 
sirup appears to prove most effective. The tendency of the ants is 
to cluster close together during the cool mornings in spring and 
autumn, especially in and about the crotch of the tree. If containers 
of sirup are present they prove a center of attraction and are frequently 
attended in large numbers. 
