52 Damage to Plant Tissue from Capsid Bugs 



also, if the cells are killed, the characteristic red brown colour should be 

 formed as it invariably is on the death of cells in apple tissue. It was 

 thought possible that Psallus ambiguus injected some substance which 

 prevented the formation of the tannin material in apple tissue, but 

 although injections were made with various substances to try and pro- 

 duce this effect, e.g. acids of varying strength, etc., these attempts were 

 unsuccessful, and almost invariably resulted in the formation of the 

 red spots and patches except in the case of strong tannic acid which 

 produced a hole surrounded by a pale margin. 



A certain species of Jassid bug found feeding on horse chestnut and 

 producing white spots thereon, was transferred to apple on which it 

 produced similar white spots; apparently these cells were not dead or 

 else, as suggested above, some substance was injected which prevented 

 the formation of the red pigment. Lefroy and Home (6), in their paper 

 upon the effects produced on plants by sucking insects, put forward 

 the theory that these white patches consist of cells filled with air. White 

 spots are characteristic of the feeding of Jassid bugs, each plant damaged 

 by them responding in a similar manner, at any rate in those cases of 

 which the writer has personal knowledge, i.e. apple, pear, chestnut, and 

 potato. 



An interesting parallel case to that of the Capsids is found in the 

 apple-feeding aphids, Aphis pomi, and Aphis sorbi; one of these has 

 little effect upon the foliage while the other (Aphis sorbi) causes curling 

 of the leaves and the formation of a very bright pink pigment which 

 is visible on the trees from a considerable distance, and which gives to 

 the Aphis its name of Rosy Apple Aphis. Sections through this rosy 

 material present an appearance exactly similar to that of sections 

 through tissue damaged by P. rugicollis, i.e. dead cells filled with a 

 granular material the only difference being in the colour of the pigment. 



Experiments were then made with another species of Capsid known 

 to be harmful to other plants, this was Lygus pabulinus, already men- 

 tioned in connection with the experiments upon potato; it is a very 

 common insect and does considerable damage to the foliage of currant 

 bushes, and produces the "shot hole" effect on potato plants. A number 

 of these bugs were taken at a very young stage and "sleeved" upon 

 apple trees, they took very rapidly to this new food and produced on 

 apple and willow injury absolutely identical with that produced by 

 P. rugicollis; the change of food plant seemed to have no ill effect on 

 the bugs, and they mostly became adults, very few dying. 



Extracts were made of the salivary glands of this insect and injected 

 into apple and willow, causing the same effect as that produced by the 



