29 



in festoons from the trees. Parts of this " wool " get blown 

 off and are carried by the wind, often for some little distance, 

 and in this material young Schizoneurce may be earned. 



Various forms of the woolly aphis are found in the course 

 of the year's cycle :- wingless females that produce live young; 

 winged females that are also viviparous ; and males without 

 wings, which pair with wingless egg-laying females. 



The wingless viviparous females are oval in shape and 

 purplish-brown in colour. Numerous white threads pass from 

 their backs. Their antennas and legs are very short, and in 

 colour are dark reddish-brown to black. Such wingless vivi- 

 parous females may be found all the year round. They give 

 rise to great numbers of young (so-called lice) which are at 

 first of a dull yellowish colour but later become purple brown. 

 It is the woolly material secreted by these that gives rise to 

 the festoons mentioned above. These lice on becoming adult 

 produce live young in turn, and a number of such generations 

 can be produced in the summer. 



The wingless viviparous females may, however, give rise, 

 between June and late October, to winged viviparous 

 females, the exact function of which has not yet been 

 discovered. Patch* appears to have shown conclusively 

 that in America these winged females, which there occur 

 commonly, migrate to elm trees, where they give rise to 

 wingless males and wingless egg-laying females. The eggs 

 laid by the latter in the crevices of the bark of the elm 

 remain over the winter, and in the spring produce wingless 

 forms from which arise aphides which attack and curl the 

 elm leaves. Subsequently the elm leaf form produces winged 

 individuals which migrate back to the apple. 



In this country there is as yet no direct evidence that the 

 woolly aphis of the apple migrates to elm, but it is of 

 interest to note that Theobald! has discovered a woolly aphis 

 which curls elm leaves and which produces a winged form 

 indistinguishable from the winged form found on apple. No 

 males or egg-laying females of this aphid have yet been; 

 discovered in this country and its relation if any to the 

 apple woolly aphis is still unknown. It is, of course, quite 

 distinct from the usual species of Scliizoneura (S. nlmi or 

 fodiens) which attacks elm and currant in Britain. 



On the apple in this country the woolly aphis produces 

 winged forms only occasionally, while wingless males and 

 females, which lay winter .eggs, are known on apple trees, 

 but are exceedingly rare. The usual method of passing the 



*Bull> 203. Agric. Exp. Station, Maine, U.S.A. 



f An account of this observation has not yet been published, but 

 Mr. Theobald kindly allows a reference to be made to it. He finds the 

 Elm form common all over Britain the top of the young shoots being 

 extensively curled. Winged forms appear in -Tune and July and fly 

 away from the Elms 



