16 THE BOLL WEEVIL PROBLEM. 
sites have led to many suggestions for practical control. Moreover, 
the parasites seem naturally to be increasing in numbers and effective- 
ness against the boll weevil. In one instance in 1907 the mortality 
due to parasites in a field near Robson, La., was 77 per cent. About 
the same time 61 per cent of the weevils in a certain field near 
Victoria, Tex., were killed by parasites. These enemies of the 
weevil have existed in this country for an indefinite time. Their 
natural habit has been to prey upon weevils more or less related to 
the boll weevil that have occurred in this country for many years. 
They never feed on vegetation. It is undoubtedly true that they are 
now turning their attention from the original hosts, which are gen- 
erally not very numerous, to the boll weevil, which offers abundant 
and favorable opportunities for reproduction. They thus ally them- 
selves with the farmer for the protection of the cotton crop. In the 
following pages numerous suggestions will be made regarding the 
means that the farmers may take to increase the effectiveness of the 
work of these parasites in reducing the numbers of the boll weevil. 
Other insect enemies—In addition to the true parasites described 
above, the boll weevil suffers from a number of insects which are not 
parasites in a strict sense but prey upon it as food. The principal 
ones of these qredatory enemies are ants. Of these, 12 species are 
known to attack the weevil. They are the minute brown ants and 
yellowish ants that occur frequently in cotton fields and are observed 
running over the plants or on the ground. Their work is not against 
the adult weevils, but against the immature stages in the squares. 
Some species devote their attention principally to the squares that 
have fallen to the ground, while others habitually seek the insects 
within the squares that remain hanging on the plants. The larva of 
the weevil, incased in a thin covering, offers a source of food that the 
ants are not inclined to overlook. They gnaw through the thin sheil 
inclosing the weevil larva and the latter is soon destroyed. In some 
cases more than half of the immature stages in fields have been found 
to be destroyed by ants alone. To find 25 per cent so destroyed is not 
a rare occurrence. In this bulletin methods will be pointed out for 
making use of these friends of the farmer and increasing the 1m- 
portant effect they naturally have in reducing the numbers of weevils. 
Other factors in natural control.—In addition to the principal factors 
in natural control which have been mentioned there are several of 
minor importance. Among these may be mentioned proliferation, 
which sometimes crushes the immature weevils, and determinate 
growth, which may prevent the development of the fall broods of the 
weevil. Attention is also called to the agency of birds in the destruc- 
tion of the boll weevil, which has been given full attention in the 
publications of the Biological Survey of this department. 
B12 
