20 NATURAL CONTROL OF THE COTTON BOLL WEEVIL. 



studied extensively in 1905, and the most important results of the 

 investigation have been published. 



The work of parasites and the possibility of making them even 

 more valuable in the fight against the weevil is considered fully by 

 Mr. W. D. Pierce in another bulletin of this Bureau. 6 The relation- 

 ship of birds to the boll weevil has been treated in several publica- 

 tions, principally by the Biological Survey. 



The study of the influence of the leaf worm upon weevil control 

 will req.iire at least another season before the results can be suffi- 

 ciently complete for publication. 



The work with proliferation was continued in 1906 only as far as 

 seemed advisable to confirm preceding results and conclusions. It 

 was found in 1905, in over 8,000 examinations, that proliferation 

 produced an increase in weevil mortality, averaging, for squares and 

 bolls together, about 12.5 per cent. From the data following in these 

 pages it appears that there is an average mortality not attributable 

 to heat or drying, ants, or parasites, among over 80,000 obser- 

 vations of squares and bolls together, averaging slightly over 12 per 

 cent. The confirmation of previous conclusions is evident, but in 

 reference to both it should be stated that the figures recorded must 

 be considered as a conservative statement of the value of this factor, 

 since it must be admitted that it may become effective in many cases 

 even before the hatching of the weevil eggs and that it is practically 

 impossible in a large series of examinations to determine whether an 

 egg or very small larva of the weevil may have .been destroyed. It 

 must also be considered that proliferation resulting from feeding 

 punctures of the weevil and of other insects frequently proceeds to 

 such an extent as to itself accomplish a destruction of both squares 

 and bolls entirely disproportionate to the severity of the feeding 

 injury which originally incited the proliferation. The value of pro- 

 liferation as a factor in controlling the weevil is therefore offset in 

 some degree by its tendency to continue beyond the remedial point 

 and by its abundant formation under certain conditions of irritation 

 when no weevil stage is present. 



The work with parasites has been sufficiently extensive to form a 

 very reliable basis for further investigations which promise to give 

 increasingly valuable results. The actual records of parasitism and 

 the comparisons between this and other factors of natural control 

 are given herewith, while the more special consideration of the con- 

 ditions favoring parasite abundance, the biological study of the 

 species found, and the possibility of increasing their effectiveness 



a Bui. No. 59, Bureau of Entomology. (See p. 8 for bibliography of proliferation.) 

 & Bui. No. 73, Bureau of Entomology. 



c Bui. No. 51, Bureau of Entomology, pp. 150-153; Buls. Nos. 22, 25, and 29, Biolog- 

 ical Survey. 



