274 HEMIPTEEA-HOMOPTERA. 



end of a month after their escape from the egg, wings are fully 

 formed. The pupae are green. The winged Psylla has four 

 transparent wings, and is usually seen about the second week in 

 June, the female being brighter than the male. In size they 

 vary from ^ to J^- of an inch. We may find adults as late as 

 October, but the majority are mature by September, when they 

 pair and deposit their eggs separately upon the bases of the 

 buds and on the youngest apple-shoots amongst the soft hairs. 

 These eggs can easily be seen in the winter, as they are pale 

 in colour. They go on laying until November. 



Prevention and Remedies. — This very injurious apple enemy 

 may easily be controlled. If a plantation is very badly infested 

 it should be sprayed in late February with lime and salt wash, 

 and again as soon as the trusses are well open with tobacco 

 wash. 



Another species, Psylla pyrivora, is now and then found on 

 pears in Britain, and is often destructive in America. 



Family ALEYRODIDJE. 



The Snow-fly (Aleyrodes brassice). 



These are also Hemiptera. They are small, moth-like, snowy 

 white, four-winged insects, with a single vein only on the front 

 wings, and their body covered with a fine white mealy powder. 

 The pupa, unlike other Hemiptera, is inactive. The commonest 

 species is the Cabbage Snow-fly {A. brassica-), found at all times of 

 the year on cabbages, beneath the leaves, where they suck out the 

 sap with their beaks, forming brown and yellow patches on them. 

 The eggs are laid singly or in a patch on the under side of a 

 leaf and hatch out in a few days. The young are covered with 

 a transparent glassy white scale which becomes opaque white 

 with two yellow spots. Beneath this scale they turn to a 

 brown pupa in from eight to twenty days, and from four to ten 

 days after the perfect insect appears. The pupal stage is pale 



