1920.] 



The Injurious Apple Capsid. 



379 



THE INJURIOUS APPLE CAPSID 



[Plesiocons rugicollis, Fall.). 



Kenneth M. Smith, 



Adviser in Agricultural Entomology, Manchester University, 



It has long been known that there are several species of bugs 

 belonging to the family Capsidae which live upon apple trees. 

 These insects feed by means of their long trunks, which they 

 push down into the tissue of leaf and fruit and use also for 

 sucking up the sap. Until recent years the damage resulting 

 from this feeding has been attributed indiscriminately to any 

 of the four or five apple-feeding species, but of late Fryer (i) 

 and Petherbridge (2) have discovered that the damage is 

 due to only one species, a green bug, Plesiocons rugicollis by 

 name. This has been confirmed by the writer in recent 

 experiments. 



Nature of Damag^e. — This bug seems to have increcLsed 

 greatly of late years, and has caused serious losses to apple 

 growers, particularly in Cambridgeshire and the Wisbech 

 district. The damage caused by the insect consists of a stunting 

 of the leaves and shoots, serious malformation of the fruit, 

 and, after consecutive attack for several years, a stunting of 

 the tree itself. In the case of the leaf, wherever P. rugicollis 

 inserts its rostrum and sucks the sap, there appears a red spot 

 which may spread somewhat and which represents an area of 

 dead cells. The young leaves and shoots are generally chosen, 

 and in a severe attack the young foliage is almost entirely 

 covered with these red spots, and in many cases growth ceases 

 and the shoots are killed. As the young apples appear the 

 capsids transfer their attentions to this fruit, and the apples 

 in their turn become covered with the characteristic red spots. 

 The only difference in this case is that the damage develops 

 further, a corky scab i^ formed, growth of the apple ceases, 

 and frequently the fruit falls to the ground. In cases 

 where only one side of an apple is punctured, the undamaged 

 •^ide continues to grow, and a badly distorted and unmarketable 

 fruit is the result. In bad cases of capsid attack the damage 

 to the fruit is very similar to, and sometimes mistaken for, the 

 fungal disease, apple scab. The object of the work here 

 described in brief was to ascertain the nature of the damage and 

 tlie reason that onlv one species produced it. 



Experiments as to the Cause of Damag^e. — There are three 

 possible explanations of this damage — (i) a purely mechanical 



