Leafy Spurge (Euphorbia esula) Genotype Affects Gall Midge (Spurgia esulae) Establishment

Greenhouse cage studies were conducted to determine the influence of shoot morphology and genetic variation on establishment of Spurgia esulae gall midge on seven leafy spurge genotypes. The genotypes were collected from South Dakota, North Dakota, Nebraska, Montana, Wyoming, Manitoba, and Austria. Genotypes from South Dakota and Nebraska were most susceptible to gall formation and had the highest larvae survival, while the genotypes from Montana and Manitoba were most resistant. Morphological characteristics of the leafy spurge stem tips, such as stem diameter, leaf length, width, and area did not correlate with gall formation or larvae survival. Chloroplast DNA restriction fragment length polymorphism analysis of the genotypes identified six chloroplast ypes among the seven leafy spurge genotypes. The two genotypes most resistant to galling by S. esulae, Manitoba and Montana, had the same chloroplast genotype, but also were closely related to the two most susceptible genotypes. Because eggs were laid on all genotypes, it appears that adult females were not preferentially selecting appropriate host genotypes, but that egg and larvae survival was strongly influenced by genotype. Nomenclature: Leafy spurge gall midge, Spurgia esulae Gagne'; leafy spurge, Euphorbia esula L. #3 EPHES. Additional index words: Biological control, rangeland weed control, cpDNA, RFLP, genetic markers, EPHES.