F. R. Petherbridge and M. A. Husain 181 



on damaged trees seems to have been regarded as sufficient evidence to 

 record it as the cause of the trouble. 



Theobald (24-28) repeatedly mentions Atractotomus mail, Orthotylus 

 marginalis and Psallus amhiguus as the culprits. Schoyen (2i) mentions 

 Orthotylus marginalis, Plesiocoris rugicoUis and Psallus amhiguus as doing 

 damage in Sweden. We do not know on what evidence these state- 

 ments are based as no details are given, but we have found that it is 

 possible to visit an orchard in which the apples have been badly marked 

 by Plesiocoris rugicoUis after this species has disappeared and when 

 one or more of the other three species are still present. We think 

 therefore that very probably the damage has been attributed to the 

 wrong species. It is of course possible that in Sweden the injury might 

 be done by a species which is harmless in this country, but in the absence 

 of direct evidence this should be regarded as doubtful. 



Fryer has pointed out that Plesiocoris rugicoUis is the more serious 

 pest and has shown by direct experiment that it causes the typical 

 damage to the leaves, and that Psallus amhiguus does uot(i2). Fryer and 

 Petherbridge also showed by direct experiment that Plesiocoris rugicoUis 

 damages the fruit and shoot and that Psallus amhiguus and Atractotomus 

 mali do not (12 a). 



Our experiments and observations show that Plesiocoris rugicoUis 

 causes marked damage to the leaves, shoots and fruit and is responsible 

 for most of, if not all, the damage in the Wisbech district, and that 

 Atractotomus mali, Orthotylus marginalis and Psallus amhiguus although 

 they feed on the juices of the apple do not cause any apparent damage to 

 the varieties badly marked by Plesiocoris rugicoUis. In no case have we 

 found either of these three species causing any visible damage to apples. 



The life-histories of a number of forms have been worked out in 

 America (6, 7, 16, ]8, 29) but very little work has been done in that direction 

 in this country. 



2. METHODS. 



Observations were made during the season of 1917 chiefly in badly 

 attacked orchards at West Walton near Wisbech where the bugs used for 

 experimental work were also obtained. Observations were also made in 

 unattacked orchards near Cambridge. 



April 14th is the earliest record of the hatching of P. rugicoUis 02) 

 so we started our visits to Wisbech at the beginning of April but 

 obtained no young capsids during the whole of this month. Twigs of 

 apple were brought back and searched for eggs. We could not find the 



