231 



This was probably the original and normal life-cycle, but whether 

 the root-system alone of the apple was used as the summer abode, 

 or both root and trunk, is not known. Most of the Eriosomatines 

 certainly pass to a subterranean stage only, and the author believes 

 that this is the normal life of E. lanigerum. From this normal life- 

 cycle others have originated, and the Aphid is known to live in four 

 different ways : — -permanently on the apple above ground, permanently 

 on the apple below ground, migrating between the root and stem of 

 apple, and living between the elm and apple. It has also been observed 

 in America migrating to mountain ash {Pyrus americanus) and to 

 Crataegus. The author has proved experimentally that E. lanigerum 

 can reproduce for at least ten years on apple, without any sexual 

 revival from the elm. 



An observation is recorded of an egg of E. lanigerum laid on the 

 apple and not on the elm ; this is evidently unusual, but occurs 

 occasionally both in Europe and America. The distinguishing features 

 of the forms of E. lanigerum found on the elm and on the apple are 

 described. 



Many records of the prevalence of the root form are quoted, though 

 this is very difficult to estimate. Reinfestation from the soil after 

 apple trees have been cleaned by spraying and painting is well known, 

 and no certain method of killing the Aphids in the soil has been devised. 

 Vaporite, naphthaline and carbon bisulphide have all proved unsuc- 

 cessful in this respect. In America, tobacco waste has been found 

 beneficial. Several growers in England have reported much success 

 with tanglefoot bands. If the bands are left on all the year, it seems 

 possible to catch all the normal ascending forms and any that may 

 descend from the progeny produced by the elm migrants. 



The appearance of Aphids in large numbers occurs spasmodically 

 in certain \^ears, but the factors regulating these general or local 

 outbreaks are unknown. The author is convinced that the soil status 

 has much to do with such increase, in conjunction with certain climatic 

 conditions. The chief means of dissemination of the insect by natural 

 factors include the flight of the alate females, wind carrying the apterae 

 in detached wool from the trees, and birds and insects carrying the 

 Aphids on their bodies. The most important artificial mode of 

 distribution, however, is undoubtedly by means of plants, especially 

 on nurser}^ stock. In examining young stock before planting, it is 

 essential to inspect the root system as well as the rest of the tree. 

 It is believed that until some apple stock has been found upon which 

 the root form cannot subsist, the pest will continue in Britain, and 

 will cause serious general or local epidemics. The relative immunity 

 of different varieties is discussed. Irish Peach, Northern Spy and 

 Winter Majetin are varieties of apple that are reported to be immune 

 from the root form, and Jonathan apples, grown on aphis-proof stock 

 from California are said never to be infested. The damage done by 

 E. lanigerum is described. 



Natural enemies in Britain seem to be limited almost entirely to 

 birds ; these include tits in winter, the tree-creeper, chaffinchs and 

 sparrows. Insect enemies on apple are almost negligible, but on elm 

 Braconid parasites and Syrphid predators destroy large numbers. 

 From the curled elm leaves, Catabomba pyrastri, Syrphus halteatus 

 and 5. ribesii have been bred. Coccinellid larvae also attack the 

 Aphid colonies on elm leaves to a less extent. 



