October, '21] lathrop: apple aphids 437 



slight because of its low toxicity upon apple, the species, nevertheless, 

 produces a heavy and conspicuous infestation, especially upon the blos- 

 som clusters, where it occurs in enormous numbers. 



In the fruit districts of the Willamette Valley, Oregon, this species 

 is rare upon apple, and each spring a thorough search has been necessary 

 in order to find even a single colony in any of the orchards in which ex- 

 aminations were made. Apparently this same condition applies in 

 California.^ However, the species occurs more or less comm.only on 

 grains and grasses in both Oregon and California. This seems to indi- 

 cate that the species is not conspicuous as an apple pest in regions where 

 the climate permits wintering on grains or grasses. 



Next to Aphis avenae, A. pomi is the m.ost abundant in apple orchards 

 of Western New York. The species increases in abundance during mid- 

 summer and young plantings as well as the more succulent portions of 

 mature trees frequently suffer severe injury. 



In Western Oregon, Aphis pomi is by no means uncommon, but severe 

 injur}^ from, this species is not of frequent occurrence. The greatest 

 abundance occurs in early summ.er; later in the season, infestation usual- 

 ly subsides to a mmimiun.. 



Aphis sorbi is by far the most common species in Western Oregon, while 

 in Western New York, it is ordinarily the least nimierous of the three. 

 Because of the high toxicity of this species upon apple, and because of its 

 habit of m.alfonning the fruit, this is a serious pest wherever it occurs. 

 The great abundance of this species under normal conditions in Western 

 Oregon ranks this insect with the codling moth as one of the major pests 

 of the apple. 



Hatching 



Spring advances rapidly in Western New York with a proportionall} 

 rapid hatching of the eggs of the aphids under consideration. The 

 gradual approach of spring in Western Oregon is accompanied by a long 

 hatching period. There is a corresponding and even m.ore striking pro- 

 longation of the intervals between the hatching periods of the several 

 species. 



During the spring of 1916 Aphis avenae began hatching in the locality 

 of Geneva, N. Y. on April 22; A. pomi on April 26, a difference of four 

 days. A. sorbi was intermediate between these two, but there was so 

 little difference in tim.e that the hatching of the two species appeared to 

 occur almost simultaneouslv. Baker and Tumer,^ working at Vienna, 



"Swain, Albert F., A Synopsis of the Aphididae of California, University of Cali- 

 fornia, Tech. Bui., Vol. 3, Xo. 1, pp. 94, 95, 1919. 



