368 



FOREST ENTOMOLOGY. 



The adult insect is greenish in colour, but head and thorax are 

 almost white, abdomen darkish. Antenna? yellowish - green, legs 

 reddish-yellow. 



Psylla alni (Linn.) 



About June 1 on an average season the tips of the branches of the 

 common alder (Alnus glutinosa) are thickly covered with a white 

 woolly down, as shown in fig. 344. These are the larva?, of Psylla 

 ahii, and may by inexperienced entomologists be classified as Aphidida?, 

 similar to American blight. The woolly covering acts as a protection 

 for the creature during the early stages of its existence. At this stage 



they are very easily disturbed, and set 

 off rapidly as large white moving specks. 

 The larval and pupal stages cannot be 

 very easily separated ; but considering the 

 more advanced stage as pupa, it is, when 

 divested of its white overcoat, rather a 

 handsome insect. The prevailing colour 

 is green, with several dark transverse 

 spots across the body. The anal segment 

 is dark. The body shows "wing humps" 

 at a very young stage. The head is not 

 conspicuously separated from the thorax, 

 nor the abdomen from the thorax. The 

 wax hairs at the anal portion of the body 

 are quite a conspicuous feature. 



The perfect insect may be found 

 throughout the whole summer. The pre- 

 vailing colour is a light-green. Head and thorax yellowish-green, 

 and studded with reddish markings ; abdomen green. Wings 

 perfectly clear. Costal and stigma veins green ; other veins some- 

 times darker. Legs green, with dark tibia? and claws. Length of 

 insect when wings are folded about 5 mm. 



The sexes can be very easily distinguished partly by the abdominal 

 structure, and also on account of the antenna? of the male being longer 

 than the antenna? of the female. 



It cannot be said that this insect is very injurious, as the summer 

 foliage does not seem to have been injured from the effects of the larval 

 and woolly secretions in spring. 



I'i.L 



344. Twig of alder injured 

 by Psylla alni. 



