VIII 



PSVLLIDAK 



579 



size of Aphidae, but in form and general appearance remind 

 one rather of Cica- 

 didae. The wings 

 are in many cases 

 even more perfectly 

 transparent than V 

 they are in many 

 Cicadidae. They are 

 sometimes called 

 springing plant-lice, 

 as their habit of 

 jumping distin- 

 guishes them from 

 the Aphidae. Low 

 has called attention 

 to the remarkable 

 variation in colour 

 they present in con- 

 formity with either 

 the age of the indi- 

 vidual, the food- 

 plant, the climate, FIG. 284. Psylla suci-inctfi. : If). Europe. (After 

 and, more particil- ^eeger.) A, larva before first moult. B, larva after 



third moult. C, adult. 



larly, the season of 



the year. 1 Beaumur long since pointed out that at their ecdyses 

 these Insects go through a remarkable series of changes of colour, 

 and Low found that this did not take place in the normal 

 manner in the winter generation that hibernates. This has 

 been confirmed by Slingerland in Xorth America in the case 

 of Psylla pyrii'nlii',- which has been introduced there. He finds 

 that there are several generations in the year, and that the 

 hibernating adults differ from the summer adults in size, being 

 nearly one-third larger ; in their much darker colouring : and 

 especially in the coloration of the front wings. 



In the earlier stages, Psyllidae differ greatly in appearance from 

 the adult forms ; the legs and antennae in the newly hatched larvae 

 are short, and have a less number of joints. In the nymph the 

 shape is very peculiar, the large wing-pads standing out horizontally 



1 J'crJ,. ~.-l. Ges. JJ'lcn, xxvi. 1876, p. 167. 



" Cornell Unir. Ayric. e;c 2 >. s'<i/l<>n . Uulldin, -U, 1892, and JJitH. 108, 1896. 



