6i8 The Insect and Allied Pests of the Hop. [nov., 



of which we are ignorant. The enormous rate of increase of 

 the Hop Aphis may be judged from the photograph repro- 

 duced here (PI. IV., Fig. 3), which shows part of a leaf 

 covered with lice, the progeny of four females in fourteen 

 days. The damage done by Aphis is twofold. Firstly the 

 insects suck out the sap of the leaves and cause them to turn 

 a sickly hue, and often to become yellowish ; secondly their 

 honey-dew and excrement fall on the upper surface of the 

 leaves and coat them with a dark, gummy mass, upon which 

 a black fungus grows. These leaves (PI. V., Fig. 1) soon 

 lose their vitality, and a " black blight" is the result. 



Life-history . — The life-history of the Hop Aphis is some- 

 what complex. The winter is passed almost entirely in the 

 egg condition on the damson, sloe, bullace, and occasionally 

 on plums and greengages. A few insects hibernate in the 

 hop hills ; these are the large fat green lice seen early in the 

 year on the hop shoots. The eggs (PI. IV., Fig. 4A) are 

 found in the clusters of buds and in their axils. They are 

 shiny black in colour, and many present a shrunken appear- 

 ance; these latter are infertile eggs. 



The young are at first green, and at once feed on the 

 tender unfolding leaves or opening blossom buds. The 

 result of their punctures is that the leaves curl up, and then 

 the lice are protected from any wash. As many as three 

 generations may occur on the prunes. In late April or May 

 many of them become nymphs; wing-buds gradually appear 

 at the sides of the body, and from the middle of May onwards 

 to early July winged viviparous females arise. These leave 

 the damsons and fly away. In some years they all leave about 

 the same time, in others in batches extending over some 

 time. Most, however, have left the prunes by the end of June. 

 Very many of these migrants settle on plants upon which 

 their young cannot subsist, and die, but those which reach 

 the hops as the so-called "fly" soon commence to produce 

 small pale living young (nits or lice) (PI. IV., Fig. 3). The 

 "fly " may settle on any leaves, but I have noticed that they 

 shelter most under the top leaves, especially amongst the 

 smallest and only partially expanded ones. There they get 

 a large amount of shelter, and are protected from any fine 

 spray. The larvae or lice soon grow to mature wingless females 



