54 Damage to Plant Tissue from Capsid Bugs » 



easily reared upon apple as shown, so that it would not be altogether 

 surprising if another pest were added to the already very long list of 

 those attacking and injuring apple trees. 



An attempt was made to find out the nature (acidity or alkalinity) 

 of the salivary juices of various harmless and harmful bugs. Some 

 specimens of L. pabulinus and P. rugicollis and Psallus ambiguus were 

 starved for 24 hours and then introduced into a petri dish containing 

 red and blue litmus paper soaked in sugar solution. The bugs would 

 not as a rule insert their stylets more than once; the result of the in- 

 sertion was to leave a brown spot on both red and blue litmus paper. 



SUMMARY. 



There are several species of Capsid bugs which normally feed on the 

 leaves and fruit of apple trees but only one causes any damage, i.e. 

 Plesiocoris rugicollis. This species produces the death of the tissue sur- 

 rounding each puncture in the leaves made in feeding and on the fruit 

 produces great distortion and "russeting." 



There are three possible explanations of this damage : 



(1) A purely mechanical injury produced by the insect's stylets in 

 process of sucking. 



(2) The possibility of the bug acting as a "carrier" of bacteria and 

 by injecting these into the plant along with the saliva so sets up a 

 pathological state. 



(3) The injection of some secretion from the salivary glands which 

 has a violently toxic effect on the plant tissue. 



It was found impossible to reproduce by mechanical means the 

 injury resulting from the feeding of P. rugicollis, also the fact that the 

 other species of Capsid bug feed in a similar manner and produce no 

 injury militates strongly against the theory of mechanical injury only. 



As regards the second theory, no bacteria could be discovered in 

 microtome sections of either damaged plant tissue or the salivary glands 

 of the bug, and all attempts to reproduce the damage by means of 

 bacteria failed. 



The third theory was proved to be the correct explanation by several 

 experiments and observations. 



Experiments were made to try and reproduce the bug injury with 

 various dilute poisons; in most cases a very similar appearance was 

 produced in the foliage, but the attempts were unsuccessful in the fruit 

 itself with the exception of the very great retarding effect in the growth 

 of the fruit, which is one of the results of the bug injury. 



By feeding the bugs on slices of potato instead of apple the same 



