The host specificity of Phyllocoptes nevadensis Roivainen (Acari: Eriophyidae), a candidate for the biological control of leafy and cypress spurges

Eriophyid gall mites have been considered for the biological weed control due to their apparent host specificity, short generation development and apparent damage. Of recent interest are mites associated with weedy Euphorbia spp, principally leafy spurge, Euphorbia esula, and cypress spurge, Euphorbia cyparissias. Surveys and eriophyid host records indicate that seven species of mites are associated with Euphorbia species in Europe. Phyllocoptes nevadensis Roivainen is a leaf rolling mite found in France and Spain and is apparently damaging to cypress spurge causing plant stunting. Studies were initiated in Montpellier, France and at Bozeman, Montana to determine the host specificity of the mite. Tests conducted in France on Croton sp, Ricinus communis, Euphorbia colbrata, E. esula (USA), E. heterophylla, E. milii, and E. cyparissias indicated that the mite may be restricted to the genus Euphorbia. To determine the utilization of species within the genus, 14 species belonging to four subgenera of Euphorbia were tested under quarantine in Montana. Mites were able to develop on nine plant species belonging to the subgenera Esula, Agaloma and Chamaesyce, including native species E. incisa, E. marginata, E. glyptosperma, E. maculata and E. serpyllifolia. Of the six accessions of North American leafy spurge tested, all supported mite development. Mites were not able to survive on the two Poinsettia species, or on the natives, E. robusta and E. corollata. Plant damage was only noted on cypress spurge and to a much lesser extent on several leafy spurge plants. Although additional information is needed to assess damage to these nontarget Euphorbia spp, the apparent lack of host specificity of the mite may lead to concerns regarding potential impacts on perennial endangered or threatened spurge species; therefore the mite is probably not suitable for release in the United States.