THEIR RELATION TO WEATHER 147 



to become dangerous. It would now require a series 

 of two or three dry seasons in succession to provide 

 for a dangerous outbreak. And this seems, in a way, 

 to measure our present ability to use diseases as a check 

 to insect increase, i.e., we can plant them where they 

 will lie dormant and ready to fall upon the insects 

 whenever conditions become favorable. Our knowl- 

 edge is as yet altogether too rudimentary to enable us 

 to predict future possibilities. 



A disease of the grasshopper has been referred to, 

 and this has formed a subject for extensive research 

 work in South Africa where the migratory forms are 

 among the most destructive pests. It was found that 

 there is a disease that sometimes appears among the 

 flying hordes and destroys enormous numbers of them. 

 This disease has been studied, has been propagated on 

 culture media, and has been distributed in pure cultures 

 with directions as to how swarms may be infected 

 through a prepared food. They depend in this instance 

 upon infecting bran, meal or a similar material with 

 the disease culture, to be exposed where the wingless 

 grasshoppers will find and eat it. They thus become 

 inoculated with the germs and establish the disease in 

 the swarms in which it afterwards spreads naturally. 

 The results on these South African forms are said to 

 be very satisfactory. The attempts to establish the 

 same disease in our American species have not produced 

 any marked results as yet. 



Scale insects are quite subject to disease attack, 

 especially in climates like that of Florida, where certain 

 of the armored scales are kept at harmless numbers by 

 fungi. One of these attacked the San Jose" or pernicious 

 scale when it was introduced into that region, keeping 

 it down without much assistance on the part of the 

 fruit-growers. Efforts to introduce this disease into 



