THE TRUE BUGS 



127 



The psyllas, or jumping plant-lice (Psyllidae), look much like 

 miniature cicadas, but are more nearly related to the true plant-lice, 

 exuding sweet honey-dew like the plant-lice but differing from them 

 in being very agile in the adult stage, giving a quick jump with their 

 strong hind legs and flying off at the slightest disturbance, whereas 

 the true plant-lice are exceedingly sluggish. The best-known example 

 is the pear psylla (Psylla pyricola\ the adult of which (Fig. 174, a) 

 is not over a tenth of an inch long but which occurs in such enormous 

 numbers that it sometimes entirely ruins large pear orchards by 

 sucking the sap from the foliage. It has been most injurious in 

 the Middle Atlantic States. It exudes a large amount of honey-dew, 



FIG. 174. The pear psylla. (Greatly enlarged, in different proportions) 

 a, adult ; 3, full-grown nymph from above ; c, egg. (After Slingerland) 



which covers the foliage and bark, on which grows a sooty black 

 fungus which is a good indication of the presence of the- pest. 



The plant-lice, or aphides (Aphididae), are the most abundant and 

 possibly the most destructive family of all the Hemiptera. Florists 

 commonly call them green-flies, which term may refer to several 

 species. Usually they are not over a tenth of an inch long, and 

 the wingless forms are more or less pear-shaped, with long legs 

 and antennae, and the common forms have two tubes projecting 

 from the abdomen, called honey- tubes. The vast amount of 

 injury done by them is chiefly due to their remarkably rapid power 

 of reproduction. During the summer the females will give birth 

 to from fifty to seventy-five young during a week or two, which 

 will become full grown in from one to two weeks. All of these 



