April, '16] HOUSER: SUBTERRANEAN FUMIGATION 285 



A NEW METHOD OF SUBTERRANEAN FUMIGATION 



By J. S. HousER, Wooster, Ohio 



Some years since while in the employ of the Cuban Agricultural 

 Experiment Station, the writer started an investigation of methods for 

 the control of the fungous-growing ant, Atta insularis, known locally 

 as the bibijagua. The studies were interrupted soon after they were 

 commenced, and were never completed, but a start was made in the 

 development of an unused principle for subterranean fumigation 

 w^hich gave evidence of such promise that it has seemed worth while 

 to place it on record. 



This ant is to Cuban agriculture and horticulture what the white 

 grub is to the northeastern quarter of the United States, i. e., the 

 most generally destructive single insect pest. In passing, it may be 

 well to note that the nature of the injury consists in the insects strip- 

 ping the foliage from plants, the mutilated leaves being taken to gal- 

 leries in the soil where they are used as a media for the growing of the 

 fungous gardens. The various species of Citrus leaves seem the pre- 

 ferred sorts, but, in the absence of these, a large number of other plants 

 are used. Occasionally an entire tree is stripped of its foliage during 

 a single night, it being the habit of this insect to confine its marauding 

 expeditions to the late afternoon and dark hours of the night. 



The herbage is piled in culture chambers located beneath the surface 

 of the ground, the average size being that of one's two clenched hands. 

 In newdy established colonies these chambers are few in number and 

 are located near the surface of the ground and there is little external 

 evidence of the colonies; but in aged, well-established colonies, the 

 ramifications sometimes extend to a depth of eight feet and a large 

 mound of earth is thrown up above. Such colonies have a number of 

 entrances, some directly above and some a considerable distance away, 

 these being reached through tunnels. The mound itself is a perfect 

 labyrinth of passageways and fungous gardens, the ants being found 

 in all parts of it. Swarming occurs in the spring at which time the new 

 queens in immense numbers emerge from the old colonies and establish 

 new ones. 



Three methods of control have been practiced, briefly described as 

 follows : 



(1) -The digging out method. — With this process, the formicary is 

 excavated and the ants and their fungous gardens are collected and 

 burned. It is expensive, laborious and only moderately successful. 



(2) The carbon bisulfide fumigation method .—With this, the liquid 

 bisulfide is poured into the openings to the nest and the fumes allowed 



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