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Baker (A. C.) & Davidson (W. M.). Woolly Pear Aphis.— JZ. Agric. 

 Research, Washington, D.C., vi, no. 10, 5th. June 1915, 1 fig. 



An Aphid which was thought to be Eriosoma lanigerum, Hausm. 

 (woolly apple aphis) and has been known to attack pear roots in 

 CaUfornia for some years past [see this Revieiv, Ser. A, iii, p. 738], 

 has proved to be undescribed and has been named Eriosoma pyricola. 

 It is beUeved that E. pyricola has been present in California for more 

 than twenty years and it is possible that this species may be found 

 in other parts of the country, notably in Oregon. It occurs over 

 practically all the pear-gro^ving areas of northern and central Cahfornia 

 and in some regions is very destructive. It lives entirely underground, 

 and the species that has been found feeding on the aerial portions of 

 pears is E. lanigerum, E. pyricola appears to attack the roots of all 

 types of pears and is especially injurious to the French wild stock 

 so largely used in California. Quince roots are attacked, but are 

 largely immune. The Kieffer stock is attacked, but it is possible 

 that Japanese stock may show immunity to a satisfactory degree. 

 Both seem more resistant than stock from France. This Aphid 

 especially attacks the smaller fibrous roots, and on trees under four 

 years old heavy infestation may result in the death of the tree. Badly 

 stunted growth and the early faUing of foliage are characteristic results 

 of attack on young trees. The majority of old infested trees do not 

 show evident injury. In orchards and districts where conditions 

 favour large numbers of winged forms or migrants, spring and early 

 summer infestations are small, indicating that few insects have passed 

 the winter in the roots. After June, such infestations multiply rapidly 

 and become very large by September, the month in which the autumn 

 migrants are produced in the greatest abundance. After September 

 there remain small wingless colonies, which increase but httle until 

 the following summer. The winged forms are produced in abundance 

 on heavy, dry, clay soils which crack in summer and autumn. Irrigated 

 orchards produce them in smaller numbers than those that receive no 

 moisture from May to October. On loam, silt, and light clay soils 

 the winged forms are much less abundantly produced, and the condi- 

 tions are generally unfavourable to such heavy infestations as occur 

 on the heavy clays. In nurseries under favourable conditions the 

 spread of the insect may be rapid. A half -acre pear nursery examined 

 in June 1915 failed to show infestation, though the Aphid was probably 

 present. In October more than half the trees examined were infested, 

 some quite heavily. Infestation in young orchards generally points 

 to the nursery as the source. 



The biology and description of this insect are given in detail. The 

 wingless and nymphal forms live chiefly on the small rootlets and less 

 frequently on the larger roots and the underground portions of the 

 suckers. The winged forms have been noticed on pear foUage and 

 on the trunk, but, with one exception, no deposition of sexual forms 

 has been observed on the pear. On cork and American elms {Ulmus 

 spp.) migrants were observed to deposit the sexual forms in cracks in 

 the bark and on the lower surface of the leaves. In one instance 

 migration from a nursery of pear trees to a group of young elms 200 

 yards distant could be traced. The migrants fly readily and strongly, 

 and are more active on warm days. On elms they are more abundant 

 (C294) Wt.P 1/106. 1,500. 9.16. B.& F.Ltd. Gp.11/3 A 



