148 INSECTS 



Illinois and New Jersey succeeded in so far that it was 

 actually established, but proved utterly incapable of 

 catching up with the insects during the hot dry spells 

 of midsummer when it rested dormant, while the scale 

 flourished and multiplied. When rains came, the tem- 

 perature fell below that needed by the disease, and we 

 found an evident case of climatic limitation. Evi- 

 dences of the existence of the disease may even now 

 be found in New Jersey in some localities, ten years 

 after it was first introduced; but it never yet cleared 

 even a single tree of scales! 



This brings up a point of some interest and much 

 importance: the length of time during which a dis- 

 ease may lie dormant and retain its virulence. On this 

 point our information is very scant; but an example 

 in illustration may be given. The periodical Cicada, 

 or " 1 7 -year locust" as it is more popularly known, 

 is attacked in the adult condition by a fungus disease 

 that attacks the body of the male, destroys the sexual 

 organs and causes the abdomen to drop, so that during 

 the latter days of a Cicada invasion a large percentage 

 of male examples will be found mutilated in this way. 

 So far as is known this disease attacks no other insects, 

 and for seventeen years it lies dormant, somewhere, 

 ready to become active again when a new brood makes 

 its appearance. 



Certain kinds of plant lice are always more or less 

 attacked by disease, and some show more diseased 

 than parasitized specimens at all times. Indeed I am 

 inclined to believe that, aside from temperature con- 

 ditions, diseases are the most effective of all checks to 

 plant lice increase; but so far as I am aware, no at- 

 tempts have yet been made to use any of them prac- 

 tically. Perhaps I should guard myself here against 

 being misunderstood. I am quite aware that some 



