50 Damage to Plant Tissue from Capsid Bugs 



The object of using potato was to produce the same reaction as in 

 the apple, but on a magnified scale. Plesiocoris rugicollis, Lygus pabulinus 

 (a species harmful to potato foliage, etc.) and Psallus ambiguus were the 

 species used. As soon as the bugs were introduced into the petri dishes 

 they commenced to feed vigorously on the potato slices. From the 

 punctures made by P. rugicollis and L. pabulinus a small drop of clear 

 fluid exudes, this drop continues to increase in size for two or three hours, 

 by which time it has attained a maximum diameter of about 3 milli- 

 metres and become greenish in colour. This drop finally dries up and 

 leaves a large area of blackened dead cells. When the harmless bug 

 sucks the potato no damage is caused to the tissues nor is there any 

 exudation of fluid. 



The explanation of the appearance of the drop appears to be that 

 the salivary injection continues to work its way in the tissue till its 

 toxic powers are exhausted, and as each cell is killed its turgidity is 

 lost and its contents exude, forming the large drop as described. It is 

 a striking fact that this exudation should only occur in the case of the 

 harmful bug. 



Plate III, fig. 2 is a photograph of potato slices which have been fed 

 upon by the bugs: A and B, by L. pabulinus; C, by P. rugicollis; and 

 D, by P. ambiguus. In A, B and C, will be seen the blackened areas of 

 dead cells round each puncture while in D, although fed upon to a similar 

 extent by Psallus ambiguus, there are no harmful results whatever. 



The following detailed observations were made of the feeding of 

 P. rugicollis and L. pabulinus upon potato. 



P. rugicollis. Times after removal of stylets from puncture. Size of 

 drop exuded, in millimetres. 



A drop of this exudation was placed upon a young apple shoot; 

 it was found to be decidedly toxic for after a. few days the shoot died. 



