Article IV. Studies on the Contagious Diseases of Insects. I. 

 By S. A. FORBES. 



Since August, 1883, the Writer has used such opportunities 

 as came in his way for observation of the diseases of insects, 

 and for more or less careful and systematic work upon them, 

 directed especially to the point of artificially propagating them 

 for the destruction of injurious insect species. While these 

 researches are not by any means completed, lacking especially 

 critical study of the bacterial forms dealt with, as botanical 

 species, and imperfect also on the side of field experiments on a 

 large scale, I have thought them worthy of present report as a 

 contribution to progress on a difficult but interesting subject, 

 especially as opportunity for further continuance of some of 

 these studies may not soon return. 



My main object has been experimental and economical, and 

 I have adopted such methods of study as seemed to me to offer 

 the simplest means of surely ascertaining whether some of the 

 common diseases of our insects were of bacterial origin, whether 

 their germs were readily and conveniently cultivable, and 

 whether such cultures could be used to convey the original 

 affections to healthy insects. 



This will serve to explain what may seem to some an ex- 

 cessive reliance on fluid cultures, much more convenient for 

 my purpose in these preliminary studies than "solid cultures" 

 with gelatine films or tubes, and quite conclusive as to the iden- 

 tity of the forms dealt with, if the cultures are often enough 

 repeated and the results are closely scanned. 



Without attempting at this time to summarize the literature 

 of the subject, scattered and chiefly fragmentary, except as 

 relates to the silkworm and the honey-bee, I give here only a 

 brief account of my own earlier notes and observations. 



The appearance of what seemed to be an epidemic of con- 

 tagious disease among the chinch bugs of Central Illinois in the 

 latter part of the summer of the above year, gave rise to an 

 article on this subject, published in 1883 in my first report as 



