80 PROLTFERATTON IN CONTROL OF "BOLL WEEVIL. 



tions, thorofore, 5 of the 7 larvii? tested reached the pupal stage. 

 This ex])eriinent 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 tliis 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 larvsB 

 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 : 



Three adults just alive, but badly deformed by pressure. 

 Two pupffi just alive, but badly deformed by pressure. 

 Two pupaj unmistakably crushed to death. 

 Twelve larvae 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, therefore, 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 conclu- 

 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 (PI. IV, 

 fig. 16) slowly but surely to crush to death the foe whose attack has 

 called forth this effort at self-defens'> on the part of the plant. Such 

 an explanation alone fidly accords with the facts as we laiow 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. 



