84 BULLETIN 965, IT. S. DEPARTMENT OF AGEICULTURE. 



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 shqwing 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 m.ove- 

 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. 



