St John's wort
St John's wort is a toxic perennial weed in Australia which spreads into woodlands and displaces pasture species. This weed threatens native floral diversity and poisons stock when grazed. Fifteen potential biocontrol agents were studied in detail, and eleven were introduced to Australia. Of these, six biocontrol agent species have established:
1. St Johns wort gall midge *Zeuxidiplosis giardi*
2. St John's wort aphid *Aphis chloris*
3. St John's wort lesser beetle *Chrysolina hyperici*
4. St John's wort greater beetle *Chrysolina quadrigemina*
5. St John's wort mite *Aculus hyperici*
6. St John's wort root borer *Agrilus hyperici*
The combined effects of these agents are expected to control and reduce the spread of St John's wort in Australia. Whilst the St John's wort aphid and St John's wort gall midge have both been released in Australia, they are yet to establish populations capable of damaging the target species. The St John's wort mite is well established and widespread, however its full distribution is yet to be mapped. The most promising agents are the St John's wort greater beetle and St John's wort lesser beetle, which have established stable populations and control St John's wort infestations in certain situations.
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