The Hop Aphis. 



79 



other hop plants, where they again reproduce themselves 

 asexually. Finally, towards the autumn most of the lice turn 

 into pupa?, and emerge as winged females and males, which 

 copulate before leaving the hop. Some of the wingless females 

 go to ground before winter and hibernate until they can resume 

 their asexual reproduction on the young hop in the spring. 



In the second cycle the winged female, after fertilisation by 

 the male in autumn, leaves the hop and flies to the sloes, damsons 

 or plums, where she deposits eggs near the tips of the shoots 

 and in the forks of the twigs. In the spring these eggs hatch 

 into lice, which in May or early June develop wings ; the winged 

 females then fly back to the hops, where they reproduce living 

 lice as before described for ten or twelve generations before 

 fresh winged forms are developed. It is the enormous rapidity 

 with which the wingless forms reproduce themselves that con- 

 stitutes the danger of an attack of the Hop Aphis ; the whole 

 plant may become completely smothered in lice if neglected for 

 a week or two. This latter cycle is the most important. 



Natural Enemies, 



The lady-birds, both in their adult and larval forms (when 

 they are known in the hop gardens as " niggers "), are great 

 devourers of aphis, and are sometimes numerous enough to keep 

 a mild attack in check. 



The lace-wing fly, which lays its white eggs in little groups, 

 each supported on a long stalk, on the underside of the leaves 

 of the hop and other plants, devours great numbers of aphides 

 when in the larval stage. 



Several species of chalcid fly are parasitic upon aphis ; 

 they lay their eggs in the living aphis, the interior of which is 

 devoured by the larvae. 



Treatment. 



The only way of dealing with the Hop Aphis is to spray or 

 " wash " the hops with a mixture containing soft soap as a basis. 

 As the aphis secretes something of a sticky or waxy nature, 

 it is not readily wetted by pure water ; the presence of the soft 

 soap causes the wash to touch the aphis, and as it dries the thin 

 layer of soft soap clogs the breathing pores and kills the insect. 

 A few growers use soft soap alone ; the majority add a decoction 



