The aim of the present study was to determine the biotype of Hessian fly which is prevalent in the SW of Spain, and to study its response to different resistance genes H. The four differential cultivars 'Monon', 'Abe', 'Caldwel' and 'Seneca' were resistant at both field and greenhouse conditions, although some variability in infestation level was detected across years. These results suggest that the prevalent biotype at the SW of Spain is 'GP'. However, we cannot discard the presence of other biotypes. Cultivars of the 'Uniform Hessian fly Nursery' (UHFN) were evaluated at the same conditions. Cultivars with H3, H5, H6, H11, H13, H21 or H24 gene were resistant, while those with H9, H10 or H12 were moderately resistant to this population. Our results are in agreement with studies of Hessian fly populations from North Africa.