422 



AN ECONOMIC ENTOMOLOGY. 



in with it. When this AustraUan insect enemy was introduced, 

 it found nothing that it recognized except the Icerya, and, in 

 consequence, devoted itself entirely to that species, totally sup- 

 pressing it in a short time. All that was done here was to re- 

 store the balance of nature, because the scale insect is a tolerably 

 rare species in Australia, owing to the number of its enemies. 

 Nothing can be argued from this case as to the possibility of in- 

 troducing foreign species to control strictly American pests with 

 which they are not acquainted. An effort was made in this 

 direction in Virginia, the object being to import European enemies 

 of bark-borers to check the invasion which seemed to threaten 

 the forests of that State. The utmost that can be said for the 

 experiment is that the imported insects have not quite died out, 

 and that occasionally one is seen out of many hundreds brought 

 in. But, on the other hand, the invasion which they were im- 

 ported to check has been disposed of by nature herself, an 

 unusually severe winter destroying the pests so completely that, 

 instead of being abnormally abundant, they have become almost 

 rarities. We can frequently do good where we have imported 

 insects, or insects occurring also in other countries, by finding 

 and introducing their parasites ; but it seems rather an Utopian 

 scheme to train predaceous insects of other countries to feed upon 

 our native species with which they are not acquainted. 



The subject of fungous or contagious diseases of insects is an 

 interesting one, but which must be dismissed here with a brief 

 reference only. We know that insects often suffer from disease, 

 and that epidemics sometimes occur among them, destroying 

 myriads. Some of these diseases have been studied, and elab- 

 orate attempts have been made, chiefly in Kansas and Illinois, 

 to make use of them practically. The chinch-bug has been the 

 insect most experimented upon ; and while it has been demon- 

 strated that it is possible to cultivate the disease and to infect pre- 

 viously healthy bugs with it, it has also developed that the 

 disease demands certain definite conditions of climate and 

 atmosphere for its own propagation. Thus, dry, warm weather 

 is unfavorable for the growth of the disease, while it favors the 

 multiplication of the bugs ; but moist or wet weather, which re- 

 tards development in the bugs, favors the disease. Until we can 

 control climatic conditions, or otherwise secure the intelligent 



