52 BULLETIN 647, U. S. DEPARTMENT OF AGRICULTURE. 



INTERFERENCE OF ANTS WITH THE WORK OF PREDACIOUS INSECTS. 



Although the ants are unable to capture in more than insignificant 

 numbers the insects predatory on the soft scales of citrus, to a con- 

 siderable extent they do interfere with their work of destroying scales, 

 as has already been indicated. This is particularly true of those 

 scales which occur in groups, such as the citrus mealybug and soft 

 brown and some other scales, the predators being unable to oviposit 

 in groups closely attended by the ants. Under normal conditions 

 the citrus mealybug, in Los Angeles County, Cal., is held in almost 

 complete control by its predacious enemies, chief of which are some 

 three or four species of lady-beetles, the brown and green lacewings, 

 and at least three kinds of predacious flies. 1 Hearings of enemies from 

 a number of large batches of mealybug material collected among the 

 ants at intervals from April to September, 1916, from scattered locali- 

 ties in Los Angeles County gave 71.8 per cent external feeders and 

 28.1 per cent parasites. 



Against the internal parasites, however, the ants appear to be 

 much less effective, as has already been indicated. Of the internal 

 parasites reared from citrus mealybugs in California by the writer, 

 only 9.7 per cent are known to be primary parasites of the mealybugs. 



NESTS AND PROTECTIVE STRUCTURES OF THE ANT. 



LOCATION AND PURPOSE OF THE NEST PROPER. 



The Argentine ant, which is very ingenious at construction, builds 

 its nest to meet the requirements of a comparatively few simple 

 needs, a primary one of which is darkness. Aside from any special 

 aversion which the ant may have to light, it seeks the darkness for 

 safety, and it is only in the dark that the workers ever rest " off 

 guard." The queens, especially the older ones, spend nearly all their 

 time where the darkness is greatest, and when moving in the trails 

 of the foragers, which they frequently do, invariably pass rapidly 

 from shelter to shelter, spending as little time as possible in the open 

 places. The ants never permit their young to remain in the light 

 for long at a time, and both they and the great mass of the queens 

 always are found in the darkest, most obscure parts of the nest. 



Another requirement of the ant is a proper regulation of tempera- 

 ture and moisture to suit its young and itself. In exceptionally dry 

 weather, such as often occurs in Louisiana from February to April 

 or May, and in California throughout every summer, the nest will 



1 The natural enemies of the mealybugs of citrus in southern California are being 

 studied by Mr. R. S. Woglum and are referred to here only in a general way, as necessary 

 to show their relationships to the Argentine ant. 



