Rubus parviflorus, R. odoratus and F2 plants from the cross R. crataegifolius x R. idaeus were resistant to R. theobaldi when exposed to the pest in an insectary or in the field. Histological studies of R. crataegifolius and one of its hybrids with R. idaeus showed that resistance was associated with a wound periderm of suberised and lignified cells, which resulted in a reticulate appearance on the cane surface, a distinctive cane feature useful for identifying resistant segregates.