16 FARMERS' BULLETIN 928. 



Once fumigation is started, it should be completed in 4 or 5 days, 

 or before possible dry weather may cause the ants to leave the traps. 

 If the number of traps is small, one man can conduct the fumigation, 

 but where there are 300 or 400 or more traps the work can be done 

 most efficiently by a crew of three, one to carry and measure the 

 insecticide while the other two remove and reset the covers and bank 

 with soil. Such a crew, working continuously, can handle 48 fumi- 

 gating covers, removing them from one lot of traps and placing them 

 over the next in from 50 minutes to one hour. Three men can 

 fumigate over 1,000 traps in 4 days. 



The same trap filler may be used indefinitely, but it and the traps 

 must be aired thoroughly after each fumigation. The filler should 

 be spread out on the ground and the traps turned up to the sun for 

 several hours before resetting. 



The cost of installing and operating the ant traps, based on the 

 prices prevailing in 1914^15, would probably run about as follows, 

 per acre of 100 trees: 



25 traps at $0.31 each $7. 75 



3 covers at $0.75 each__ 2. 25 



Net cost of traps and fumigating covers per acre 10.00 



In practice a crew of three have fumigated 400 traps in 11 8-hour 

 days ; their services, at the rate of $1.25 per day each, cost $5.62. The 

 price of carbon disulphid prevailing in 1915 was $10.75 per hundred 

 pounds. On this basis the cost of fumigation, with the use of 25 

 traps per acre of 100 trees, would be about as follows : 



Cost of labor, fumigating 25 traps at $0.014 each $0. 35 



Cost of insecticide, 25 traps at $0.013 each . 325 



Net cost of fumigation per acre . 675 



From five to eight fumigations about one month apart will be 

 necessary to reduce the ants to an inconsiderable number in the 

 orange grove. 



USE OF DRAINAGE DITCHES TO PREVENT REINFESTATION. 



The orange grove will be rid of ants more rapidly if reinfestation 

 is prevented by means of barrier ditches. This means of preventing 

 the spread of ants is well known in Plaquemines Parish, where some 

 of the growers have adapted drainage ditches to this use. Where 

 drainage ditches already have been dug around three sides of the 

 orchard, as is the case in many orchards, they need only to be cleared 

 of weeds and provided with divided bridges which ants can not cross 

 (figs. 4 and 5) to adapt them for use against ants. On the lower land 

 subsurface water will remain in the ditches practically throughout 

 the rainy weather. In higher sections it will be necessary at times to 

 flood the ditches with water from the river by means of rice-irri- 



