LEAFY SPURGE (EUPHORBIA-ESULA) GENOTYPE AFFECTS GALL MIDGE (SPURGIA-ESULAE) ESTABLISHMENT

Greenhouse cage studies were conducted to determine the influence of s hoot morphology and genetic variation on establishment of Spurgia esul ae gall midge on seven leafy spurge genotypes, The genotypes were coll ected from South Dakota, North Dakota, Nebraska, Montana, Wyoming, Man itoba, and Austria, Genotypes from South Dakota and Nebraska were most susceptible to gall formation and had the highest larvae survival, wh ile the genotypes from Montana and Manitoba were most resistant. Morph ological characteristics of the leafy spurge stem tips, such as stem d iameter, leaf length, width, and area did not correlate with gall form ation or larvae survival. Chloroplast DNA restriction fragment length polymorphism analysis of the genotypes identified six chloroplast type s among the seven leafy spurge genotypes, The two genotypes most resis tant to galling by S. esulae, Manitoba and Montana, had the same chlor oplast genotype, but also were closely related to the two most suscept ible genotypes, Because eggs were laid on all genotypes, it appears th at adult females were not preferentially selecting appropriate host ge notypes, but that egg and larvae survival was strongly influenced by g enotype.