517 



Apart from parasites, the best means of reducing this pest seems 

 to be to run a mowing machine over the crop so as to cut off the tops 

 as close to the crown as possible when the second generation is in the 

 pupal stage, i.e. in the beginning of September. The tops must be 

 burnt or buried before the middle of September, when the moths 

 emerge. The eggs are laid too low to be reached in this manner, 

 but may be destroyed by ploughing. Old beds should not be ploughed 

 up until after the eggs are laid in November, for if this is done earlier, 

 the moths will probably lay their eggs on neighbouring crops of 

 strawberries, or on wild plants of Fragaria and Comarum. 



Smith (K. M.). Investigation of the Nature and Cause of the Damage 

 to Plant Tissue resulting from the Feeding of Capsid Bugs. — 



Ann". App. Biol., Cambridge, vii, no. 1, September 1920, pp. 40-55, 

 1 plate, 5 figs. 



The author's summary is as follows : — There are several species 

 of Capsid bugs that 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 surrounding 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 the 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 

 setting 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 Capsids 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 explanation proved to be the correct one from several 

 experiments and observations. 



Experiments were made to 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 oti slices of potato instead of apple the same 

 ■effect was produced, but on a magnified scale. The salivary glands 

 of P. rugicollis and of Lygus pabulinus, a bug harmful to potato foliage, 

 when placed on a freshly cut slice of potato in a petri dish, produced 

 a violent reaction which killed much of the surrounding tissue. The 

 same experiment was carried out with the glands of one of the harm- 

 less apple-feeding bugs, Psallus ambiguus ; these had no effect whatever 

 >on the potato. When the salivary glands of P. rugicollis were pricked 



