36 BULLETIN 965, U. S. DEPARTMENT OF AGRICULTURE. 
winter colonies in the spring, their instinct to multiply leads to an 
aggressive search for food at a time when the supply is scarce. Con- 
sequently, they feed ravenously at this time on ant sirup when offered. 
It is also during the spring and autumn that the night temperature 
approaches 50° F., which reduces ant activity, causes the ants to 
congregate in or about tree crotches of the main limbs, and greatly 
increases feeding, particularly in the case of trees infested with 
honeydew-producing insects. During the hot summer months, 
when the temperature seldom drops to 50° F., ants are active both 
night and day, and where other food is available they are not greatly 
attracted by the poisoned sirup. 
This temperature influence, and the further important considera- 
tion that scale control by fumigation is confined largely to the autumn 
months, make the fall and spring desirable periods for poisoning the 
Argentine ant. The writers recommend that control be started 
between the time ants first appear in the spring and July 1 , or from 
the last of September until congregation into winter colonies takes 
place. The time of the appearance of ants in the spring varies 
from year to year, as well as from locality to locality. In 1916 ant 
activity started the last week in February, whereas in 1920 it was 
about the middle of April before the winter colonies began to break 
up. With the approach of cold weather, which normally sets in 
during December, ants disappear from the trees, although in a very 
open winter, as that of 1917, complete winter colonizing does not 
occur. 
Reappearance of Other Ants Following Control of the Argentine Species. 
It has been stated by Newell that the Argentine ant will not tolerate 
the presence of other species of ants within its domains. In southern 
California the commonest species of ant in citrus groves not entirely 
overrun with the Argentine ant is Prenolepis imparis Say. Formica 
cinerea Mayr, var. pilicornis Emery ranks second, and Tapinoma 
sessile Say, Dorymyrmex pyramicus Roger, and Cremastogaster 
lineolata Say, var. calif omica Emery are of lesser importance. 
Orchards long infested with Argentine ants are entirely freed 
of these other species. The reappearance of Prenolepis imparis 
closely following the eradication of the Argentine ant has often been 
noted, particularly during the autumn and early winter months. 
One striking instance occurred in 1918 at Pasadena, where ant 
control was started in April on 258 trees, 4 of which were frequented 
with Prenolepis. These four infestations of Prenolepis were eradi- 
cated, and the Argentines on the other trees were brought under 
control during the summer and totally eradicated during the month 
of November, with the exception of a few trees in one corner. On 
October 17 Prenolepis reappeared on 1 marginal tree and by Novem- 
