Regular close inspection of lily and fritillary plants from early spring onwards is the best way to avoid a build up the beetles and their larvae.
Pick adults off the plants by hand where you can.
If the infestation is not large and you’re able to keep an eye on them, leaving them could be a good option to allow a natural balance of predators to build up in your garden to control them for you.
Making your garden more wildlife friendly to encourage birds, ground beetles, wasps and frogs would be a great help as all of them will feed on the larvae.
Some lilies are sold as being lily beetle tolerant, such as ‘Defender Pink’.
There are chemical controls available at some garden centres to help control infestations, but ideally non-chemical controls should be used first. If chemical products are chosen, then they should be used only where absolutely necessary. Take great care when applying to limit the areas of plants sprayed, following instructions on the label.
There are also some organic insecticides available to help reduce the number of the pests on the plants.