48 Damage to Plant Tissue from Capsid Bugs 



(1) Dilute ammonia. 



(2) Chloroform. 



(3) Various dilute acids, such as hydrochloric, etc. 



(4) Xylol. 



In each case the leaf assumed a spotted and patched appearance, 

 very similar to the effect produced by the Capsid, and the leaves were 

 put back in their development to a similar extent, while if pricked with 

 the fluid so that more than 25 per cent, of the area of the leaf was affected, 

 the leaves died. The characteristic red spots appeared on the apple 

 leaves and the clear patches of dead cells appeared on the willow. 



The same injections were made into the apple fruit itself, the chief 

 result being the extraordinary retarding effect on the growth of the 

 apple; after a week or ten days the control fruit was twice to three 

 times the size of the pricked fruit, and in many cases the inoculated 

 specimens fell off after ten days or a fortnight. 



Further experiments were made to prove conclusively if possible the 

 harmful effects of the salivary juices of Plesiocoris rugicollis. A number 

 of the harmful Capsid bugs were ground up in a sterile mortar with a 

 single drop of sterile water and the resulting fluid injected into apple 

 and willow leaves. At the same time and into the same trees, a similar 

 fluid, made from harmless apple Capsids, was also injected, in each case 

 with a sterile water control. This experiment was unsatisfactory, no 

 conclusive results could be drawn from it. A certain amount of damage 

 was done in each case, possibly slightly more in the case of the extract 

 of the harmful bug than in the other, but it seems probable that the 

 harmful substance in the salivary glands was so diluted or neutralised 

 by the other juices of the body or by the sterile water as to lose its 

 toxic effect. 



The same experiment was repeated, this time without the sterile 

 water but again with unsatisfactory results. 



Finally the whole salivary apparatus was removed from harmful and 

 harmless bugs and pricked into the leaf tissue. This was definitely satis- 

 factory, as the glands of the harmful bug (P. rugicollis) were very much 

 more toxic than those of the harmless bug (P. ambiguus) which had 

 little or no effect. The salivary apparatus of the injurious insect was 

 placed on a young apple leaf and a small prick with a sterile needle 

 made through it into the tissue beneath. In an hour or two the cells 

 underlying the gland were all killed and by the next morning 50 per cent, 

 of the leaf was dead : a similar prick made through the glands of a harm- 

 less Capsid under similar circumstances produced no effect whatever. 



