Evidence for resistance in Hypericum perforatum to a biological control agent, the eriophyid mite Aculus hyperici
P.W. Jupp, D.T. Briese and J.M. Cullen, CSIRO Entomology and Co-operative Research Centre for Weed Management Systems, GPO Box 1700, Canberra, ACT 2601, Australia.
Abstract
The eriophyid mite, Aculus hyperici, was released in Australia in 1991 for the biological control of St. John's wort, Hypericum perforatum. Establishment was variable, with some sites showing rapid increases in mite populations to levels at which plant damage was observed after two years, while others failed completely. Differences could not all be explained in terms of climate or release site conditions. Two laboratory experiments were set up to determine whether different forms of the target weed might show differences in susceptibility to attack by A. hyperici to measure the impact of the mites on these forms. Overall, there was a negative correlation between mite density and both host-plant root and shoot biomass, demonstrating the impact of A. hyperici. However, populations of the mite remained very low on plants collected from three of the eight regions tested, including sites where establishment failed in the field. It was concluded, that variable host-plant susceptibility may influence the impact of this highly promising agent, and needs to be monitored carefully.
Plant Protection Quarterly (1997) 12 (2) 67-70.