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INVESTIGATION OF THE NATURE AND CAUSE OF 



THE DAMAGE TO PLANT TISSUE RESULTING 



FROM THE FEEDING OF CAPSID BUGS. 



By KENNETH M. SMITH, A.R.C.S., D.I.C. 



(Adviser in Agricultural Entomology, Manchester University.) 



(With 1 Plate and 5 text-figures.) 



This piece of work was suggested by Mr J. C. F. Fryer, entomologist 

 to the Ministry of Agriculture and was carried out at the Royal College 

 of Science, S. Kensington, under Prof. H. Maxwell Lefroy. 



I wish to acknowledge my indebtedness to Prof. Blackman and 

 Dr S. G. Paine, of the Imperial College of Science and Technology, for 

 much valuable assistance and advice. 



The object of this investigation was to discover the causes of the 

 damage to plants and especially to apple trees from the feeding of 

 Capsid bugs. There are many species of Capsids which normally feed 

 on the fruit and leaves of apple trees in this country, those which have 

 attracted most attention being the following: Plesiocoris rugicollis, 

 Atractotomus mali, Orthotylus marginalia and Psollus ambiguus; only 

 the first-named causes any damage to the fruit and foliage (Fryer (l), 

 Petherbridge and Husain(2) and others). Lygus pratensis also is found 

 by Collinge(3), to cause damage to the apple fruit itself by depositing 

 its eggs in the lenticels, but not by sucking the juices. The problem to 

 be solved is, then, as follows. There are four species of Capsid bugs, 

 mostly closely allied, all feeding on apple fruit and foliage and feeding 

 by the same process, i.e. by inserting their mouth-parts into the tissue 

 and sucking the sap, yet only one of them, Plesiocoris rugicollis, causes 

 any damage. 



P. rugicollis hatches out in May, and the young Capsids immediately 

 begin to feed voraciously, picking out the young shoots which soon 

 become covered with spots and patches of dead cells ; this has the effect 

 of keeping back the shoots and young leaves to a very large extent, and 

 in some cases causes the death of the whole shoot. When the young 



