THE EFFECTS OF HERBIVORY BY A MITE, ACULUS-HYPERICI NUTRIENT DEFICIENCY ON GROWTH IN HYPERICUMSPECIES

The combined effects of herbivory by a mite, Aculus hyperici Liro, and a deficiency of nutrients on plant growth were measured for Hypericum perforatum L. and H. gramineum J.Forst. grown in a glasshouse. The re sults are discussed in relation to the biological control of H. perfor atum, an introduced weed in southern Australia, relative to growth of its indigenous congener, H. gramineum. Growth of both species was redu ced when infested with the mite, although the growth of H. perforatum was reduced by more than that of H. gramineum. Nutrient deficiencies a lso reduced growth of both species, especially of roots. Imposition of nutrient deficiency on mite-infested plants caused multiplicative red uctions in plant growth equivalent to the product of the proportional reductions caused by either herbivory or nutrient deficiency alone.