380 



The Injurious Apple Capsid. 



[JULY,. 



laceration of the tissue by the mouthparts of the bug in the 

 process of feeding ; (2) the introduction into the plant of bacteria 

 along with the salivary juices, which then set up a disease ; 

 (3) the introduction into the plant of some chemical substance 

 or enzyme, which causes a reaction with the juices of the plant. 

 A number of experiments were performed to ascertain which of 

 these theories was the correct one.* 



The results of these experiments proved conclusively that 

 the damage was caused by some chemical substance or enzyme 

 in the salivary juices of Plesiocoris rugicollis peculiar to this- 

 species among those bugs normally feeding on apple. This 

 chemical substance or enzyme is injected into the juices of 

 the apple along with the secretion from the salivary glands, 

 and sets up the violent reaction above described. 



Lygrus Pabuiinus. — ^There is another green bug of the same 

 family, and closely allied to P. rugicollis, namely, Lygus 

 pabuiinus, which normally feeds upon herbaceous plants, as 

 for instance, potatoes, and the injury it produces affords a 

 parallel case to that caused by P. rugicollis on the apple. 

 Although L. pabuiinus feeds upon potato during the summer, 

 in the early part of the year it lives upon red currant and 

 gooseberry, from whence it migrates to the potato, and in late 

 autumn turns its attention to the artichoke. The writer has 

 found it upon red currant, black currant, gooseberry, pear, 

 potato, bindweed, dock, plum, among other plants, and under 

 experimental conditions has reared it to adult life from the 

 first stage (or instar) upon apple and willow, the two food plants 

 of Plesiocoris rugicollis. These facts are mentioned in order 

 to show the danger to be apprehended from this family, conse- 

 quent upon the changing of the host plant. The reasons for 

 these changes of food plants are not known, but it would be well 

 to recognise the possibility of capids such as Lygus and its 

 allies suddenly developing a taste for fruitarian diet. 



Further information as to the life history and control of 

 the Apple Capsid is given in the Ministry's Leaflet No. 319. 

 The following methods of control of this insect are recom- 

 mended in the leaflet : — 



Methods of Control.— Apple Capsids are difficult insects to con- 

 trol, but the damage can be greatly reduced by careful spraying. 

 The work, however, must be well done, for it h necessary to 

 wet each bug with the spray fluid — not an easy matter when they 

 are sheltering between the flower buds in the trusses or among 



* For a detailed account of these experiments, see the- \\Titer's paper in 

 the Annals of Applied Biology of this year. 



