36 PROLIFERATION IN CONTROL OF BOLL WEEVIL. 
tions, therefore, 5 of the 7 larve tested reached the pupal stage, | 
This experiment was performed between November 17 and December 
12,1905. The larval stage averaged about thirty days in duration. It | 
does not follow from the length of this stage that the food conditions | 
were even unfavorable, since at that season in bolls the length of the | 
larval stage would undoubtedly exceed thirty days under normal field 
conditions. These experiments alone would be sufficient to prove 
that the mortality caused by proliferation is not due to insufficient | 
nutrition or to poisonous qualities in the food material of the larva 
affected. Furthermore, the examination of thousands of squares and _ 
bolls has shown that in a very great number of cases weevils reach 
maturity in the field on no other food than proliferous cells. | 
MECHANICAL CRUSHING THE REAL METHOD. 
The real cause of death in the presence of abundant proliferation will | 
become apparent to any one who will take the pains to examine care-_ 
fully a few thousand bolls which have been injured by weevil attack, | 
In one series of observations, covering 1,800 bolls, 1,016 weevil stages — 
were found. During this examination a partial record was kept of | 
those cases in which the cause of death was unmistakably shown, with | 
the following result: P| 
Three adults just alive, but badly deformed by pressure. 
Two pupe just alive, but badly deformed by pressure. 
. Two pupe unmistakably crushed to death. 
Twelve larve unmistakably crushed to death. | 
These 19 cases formed nearly 2 per cent of all the stages found. The 
record was not kept by all those engaged in the examination of this” 
series of bolls and only the most unmistakable cases were recorded at 
all. It is certain, thercfore, that this 2 per cent is but a small part of — 
the true proportion of weevils which were killed in this way by the | 
proliferation. Considering these facts in connection with the conelu- 
sions as to the food quality of proliferous cells, it seems safe to conclude ~ 
that the great majority of deaths due to proliferation may be caused | 
by the mechanical effect of the formation in first enveloping the larva 
so closely as to prevent its movement (PI. IV, fig. 15), and then the} 
continued formation producing sufficient internal pressure (Pl. IV, } 
fig. 16) slowly but surely to crush to death the foe whose attack has | 
called forth this effort at self-defense on the part of the plant. Such 
an explanation alone fully accords with the facts as we know them. | 
These observations present to us in a very vivid way an illustration } 
of the intensity of the struggle, continually going on between plant ) 
and insect life. It is a life and death struggle, and it is not always the 
insect that wins. ct 
