30 INSECT ENEMIES OF THE BOLL WEEVIL. 



tions. Several other varieties have been noticed to have this 

 same tendency, but they have not the other characteristics to recom- 

 mend them. In this connection we refer the reader to section 4 

 (p. 21), in which it has been shown that at least two States have had 

 a liigher average control of the boll weevil in hanging squares than in 

 fallen squares when all of the records available are considered. It 

 will also be noticed in section 5, under Table XI, giving the actual 

 control of the boll weevil in 1908, that hanging squares and hanging 

 bolls were decidedlj^ in the lead in the total control over either fallen 

 squares or fallen bolls. While this has not been the case in the other 

 years under consideration, we nevertheless consider that the pres- 

 ence of a nursery for the parasites in the field is most desirable. 

 Undoubtedly these hanging squares constitute such a nursery. 



6. A STUDY OF HOW AGRICULTURE MODIFIES INSECT CONTROL. 



From studies made during 1907 the follomng comparisons may 

 be made to show the number of factors that it is actually necessary 

 to consider in order that differences in parasitism ma}' be understood. 



At Arlington, Tex., records were kept on a field in the red loam 

 post-oak country or "cross timbers," another in the Trinity River 

 bottoms, and a tliird on the black waxy prairie. The first was 

 planted March 12, the second April 1, the third April 5. On August 

 28 the weevil infestation of squares in the timbers was 80.5 per cent, 

 in the bottoms 94.3 per cent, and on the prairie 21.4 per cent. At 

 the same time the parasitism in fallen squares on the timbers was 3.12 

 per cent, in the bottoms 1,9 per cent, and on the prairie 2,56 per cent. 

 In the timbers the parasitism of hanging squares was 39 per cent and 

 in the bottoms 24,78 per cent. The variable factors are soil, flora, 

 time of planting, variety of cotton, and weevil abundance. Hang- 

 ing squares were found in 1906 to be more highly parasitized in 

 timber land than on the prairie, and fallen squares inversely. There 

 appears to be an indication of the value of early planting. This 

 first field was the earliest field known in the vicinity and it showed 

 a high parasitism in hanging forms throughout the season. 



At Calvert, Tex., were two fields on the prairie, one planted March 

 11 and 12, the other April 1. On June 21 the weevil infestation of the 

 first was 18 per cent and of the second 21 per cent. On July 5 the 

 parasitism in the first was 2 per cent and in the second nothing. 



Ait Dcnison, Tex., were two fields, one in the red clay, the other on 

 sandy loam, neither surrounded by timber. On the first the stalks 

 were burned February 28, on the second March 15. Both were 

 planted March 30, On August 27 the weevil infestation on the 

 first was 88.3 per cent, on the second 87.6 per cent; the parasitism in 

 fallen squares on the first was 6.31 per cent, on the second 2.85 per 



