148 THE MEXICAN COTTON-BOLL WEEVIL. 



LABORATORY EXPERIMENTS IN BURIAL. 



In an experiment performed at Victoria, Tex., in 1904, 1,000 

 infested squares were buried under from 2 to 5 inches of well-pul- 

 verized earth. 1 Seventy-five weevils emerged. Twenty-seven wee- 

 vils were found which had been unable to reach the surface. Their 

 location varied from the bottom of the receptacle to just beneath 

 the surface. The weighted average of the distances covered by the 

 weevils which failed to reach the surface was 2 inches. 



In another series of experiments at Victoria, Tex., 74 squares were 

 placed under wet soil. It was found that 16 per cent of the weevil 

 stages were killed. Of the weevils which became adult 30 per cent 

 emerged from the squares, but only 23 per cent reached the surface 

 or escaped from an average depth of 1 inch. In these experiments, 

 considering all the weevil stages present, 35 per cent died without 

 escaping from the soil. 



In 1904 Prof. E. D. Sanderson performed a number of burial 

 experiments at College Station, Tex. At from 0.5 inch to 1.5 inches 

 below the surface 26.7 per cent of the weevils emerged; at from 2 

 to 4 inches 4.7 per cent reached the surface. 



It will be noted that these laboratory experiments substantiate the 

 conclusion drawn from the field experiments described previously 

 regarding the greatly increased mortality brought about by deep 

 burial and by moisture. 



BURIAL OF ADULT WEEVILS AT TIME OF HIBERNATION. 



On or after November 23, 1903, at Victoria, Tex., 1,000 adult 

 weevils were buried under from 2 to 6 inches of soil which contained 

 from 9 to 19 per cent of water. Only five of these weevils succeeded 

 in reaching the surface. Four of those which escaped and one which 

 was still buried in the earth were found alive when examination was 

 made on March 16, 1904. All the remaining weevils appear to have 

 died where they were buried. 



CONCLUSIONS FROM BURIAL EXPERIMENTS. 



The field and laboratory experiments to which references have been 

 made indicate that the boll weevil has comparatively little ability to 

 emerge from moist soil, while dry, partially pulverized soil offers 

 small obstacles to their emergence. The experiments also show that 

 burial, even under moist conditions, would have to be as deep as 2 

 inches to bring about very decided results. The practical question 

 therefore is whether in cotton fields the soil can be turned over to 

 a depth of 2 inches during the growing season without injury to the 

 crop. As is well known, one of the most important cultural methods 

 in producing cotton is shallow cultivation. The reason for this is 

 that the plant sends many lateral roots almost at right angles from 

 the rows and at a very short distance beneath the surface. Many 

 of these lateral roots lie only 2 or 3 inches beneath the ground. If 

 they were disturbed, the plants would react by shedding the squares. 



Undoubtedly the loss of fruit from this cause woidd more than 

 offset any possible advantage accruing from the destruction of the 



1 Much more thoroughly pulverized than would be the case in the field. 



