248 AjJiple mid Pear Sucker 



Mr Awati left for India and had not time to fully revise the text, 

 so I have done so. I also express herewith our acknowledgments to 

 Sir John Wolfe-Barry, whose generous provision of the studentship 

 made possible Mr Awati's paper on the Mechanism of Suction in Lygus 

 pabulinus {Proc. Zool. Soc. London, 1914, p. 685) and the present paper. 

 I hope that the work on apple sucker will be of value to fruit-growers 

 in England, and I think the method of checking it is a real advance on 

 anything hitherto used in this country. 



H. M. LEFROY. 



The Apple Sucker {Psylla mali). 



I. Egg to Larva. 



{a) Distribution of Eggs (Fig. 21). (Black dots on t\\dgs represent 

 eggs of Psylla mali.) The eggs are laid singly on the twigs of the apple 

 trees. They are never found in clusters or groups, but on the contrary 

 they are irregularly distributed on the twigs, which are chosen according 

 to their age. It seems that new twigs (of the first year's growth) are 

 chosen by the female on which to lay the eggs. In some cases I have 

 found that the eggs are deposited on one side while the other is tolerably 

 free from them. It is possible that light may have something to do 

 with this kind of deposition. The eggs are found along the scars (on 

 a twig) left on the leaf petioles. 



(6) Description (Fig. 1). An egg of Psylla mali is oblong, tapering 

 to both ends. It is sculptured into fine little circles. It is pale white 

 when laid, but begins to change colour when it nears the hatching 

 season, then it becomes distinctly pale brown or reddish. At one end 

 there is a long stalk which hangs free in the air, while at the other there 

 is a sucker-like expansion which glues the egg to the twig. Its position 

 on a twig is such that its long axis lies parallel to that of the twig. 



(c) Hatching. The eggs begin to hatch when spring sets in. If 

 the weather is warm before the spring they may hatch earlier, but 

 generally the larvae begin to come out in the last week of March. I have 

 seen an egg hatching on March 23rd ; the hatching may go on for some 

 time, until the last week of April. 



{(l) Mechanism. The eggs are split up longitudinally (Fig. 2). 

 It seems that there is some mechanism, which is shared partly by the 

 egg and partly by the larva. The spot where the larva comes out is 

 provided with minute teeth which from either side form a dovetailing 



