F. R. Petherbridge and M. A. Husain 195 



damage is done to it by them^ but the adults do most of the damage to 

 the shoots. Where the young stem is attacked a brown fluid oozes out, 

 the stem often cracks and is in some cases killed. When the terminal 

 shoot is killed several of the buds below form shoots and a very thick tree 

 results, especially when young trees are attacked. Most of the damage to 

 the fruit is done by the Instars IV and V. 



Wherever a P. rugicollis in any stage sucks a leaf a purplish brown 

 spot appears after a short time, at first round but soon becoming 

 irregular. The spot becomes irregular by spreading to the nearest small 

 veins which form the boundaries of the spot and thus the shape of the 

 marking is determined by the small veins between which the puncture is 

 made. The area covered by the spot becomes thinner and sinks below 

 the normal level of the surface of the leaf. 



In older leaves the marking does not spread much but remains as a 

 small spot. In all cases cork formation takes place round the seat of 

 injury. When the puncture is very deep the whole of the mesophyll is 

 affected, but in some punctures from the upper surface only the upper 

 part of the mesophyll was injured and in some punctures from the lower 

 surface only the lower part of the mesophyll turned brown. In many 

 cases the epidermis over the brown spot appeared to be normal. Sections 

 of injured leaves show that the mesophyll dies first and the epidermis 

 afterwards. A badly damaged leaf sometimes remains shrivelled and 

 eventually dies. Some badly damaged leaves do not die but remain 

 crumpled and deformed, the dead tissue falling out and leaving a number 

 of holes with a brown margin. In several trees of the variety Grenadier 

 the leaves were so badly punctured that very little growth was made 

 until late in the season. In a mild attack the leaves may grow fairly well 

 whilst showing the small brown marks. Occasionally a vein is punctured 

 and a brown spot results. 



The injury to the fruit varies with the variety. In the slower growing 

 varieties like Lady Hollendale and Worcester Pearmain the damage is 

 enormous and badly marked apples do not grow even to one-quarter of 

 their normal size and often fall off. In the quicker growing varieties like 

 Bramley's Seedling and Early Victoria the fruit grows out of the injury 

 more, and although corky markings and peculiar shaped apples may 

 result, the reduction of the crop is not nearly so marked. 



When a bug punctures the young fruit a small drop of fluid exudes 

 from each puncture. These drops eventually dry up and leave a brown 

 mark in the fruit (see PI. XI, fig. 13). The tissue around the seat of injury 

 forms cork and is therefore prevented from making normal growth. 



