Abstract
The reaction of various grape cultivars to gallicoles of the grape phylloxera, Phylloxera vitifoliae (Fitch), collected from various sources showed that at least 2 strains of the insect occur in Ontario. Strain I, originally collected from the cultivar 'Seibel 7053,' caused necrosis but not galls on the cultivar 'Maréchal Foch' and on Vitis riparia X rupestris 3309. Isolates of phylloxera from Vitis riparia Michx. and the cultivars 'Seibel 10878' and 'Clinton,' though differing slightly in their effect on Foch in some tests, appeared basically similar to strain I. Strain II, originally collected from Foch, caused galls without necrosis on Foch and 3309. An isolate from 3309 caused galls, and in some tests necrosis, on Foch, but it did not differ from strain II in other tests. All isolates tested caused galls on S-10878, S-9110, S-7053, Clinton, and V. riparia.

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