55 



to infection from other sources need not be stated here, because the 

 important point is that, in either case, the results thus attained natu- 

 rally are for this species, probably the best possible even by the cooper- 

 ation of artificial means. This is in reference only to any possible in- 

 sect diseases already found in the region where the Boll Worm depre- 

 dates on cotton. 



The only hope then would seem to be the introduction of a foreign 

 disease, or at any rate one not already found in the infested regions. 

 This was thought to be the case with the Cabbage Worm disease. 

 This disease, even in localities in the South where it is prevalent, pro- 

 duces no wholesale exterminative destruction of that species. This 

 disease in itself, then, nnder the local existiug circumstances, is not ot 

 that virulent kind necessary in most cases for the infection of a new 

 pest in a new locality. (This is only generally speaking, and is not to 

 be understood as meaning that a disease virulent in one species will be 

 equally so in another, or that a disease mild in one pest might not be 

 virulent in another.) Furthermore, the Cabbage Worm disease is 

 already found in a mild form in some portions of the cotton belt; also, a 

 very prevalent disease of the Cabbage Plusia (Plusia brassicw), and 

 which is probably the same as the Cabbage Worm disease. Small 

 patches of cabbage are found here and there at quite frequent intervals 

 throughout most of the cotton plantations, a condition resulting from 

 the system of small negro tenantry prevalent among Southern planters. 

 Thus every opportunity is offered for the spread of the disease in ques- 

 tion in case it were highly contagious and of practical economic import- 

 ance in this connection. In fact it has been found that the Boll Worm 

 is occasionally found to be diseased. From symptoms and other bac- 

 teriological evidence it is now quite definitely determined to be identi- 

 cal Avith the Plusia and Cabbage Worm disease. It is quite probable, 

 therefore, that these diseases are already doing their work as exten- 

 sively as is possible under the specially peculiar circumstances already 

 mentioned, and which are such as to quite effectually baffle artificial 

 means. 



The importance of the work with insect diseases is not to be under- 

 estimated, however. The work which it was possible to do simply dem- 

 onstrates that by mere contagion and transmission no great and won- 

 derful results are to be obtained. Bather in this case the question 

 becomes one of virulence, and not merely susceptibility to infectious 

 diseases. One acquainted with bacteriological methods knows that 

 . these two objects can not primarily be accomplished simultaneously in 

 a single investigation; that is to say that the question of the in efficacy 

 as a practical economic measure by the transmission of any contagious 

 disease must be determined first, and then attention is given, if the 

 pest is found susceptible, to those conditions which might increase the 

 virulence of the disease-producing germs in question. The work, there- 

 fore, so far as followed out ? is thorough and conclusive, but from the 



