The scarlet lily beetle may look attractive, but it is the scourge of lily growers. It can do huge amounts of damage to lilies and needs to be controlled whenever it is seen.
Both the adult scarlet lily beetles and their grubs eat holes in the leaves of lily plants often leading to leaf drop that weakens the plant. As a result, over time, the bulbs become smaller and flowering in subsequent years is reduced.
They will also eat flower buds, leading to a reduction or complete failure of the flower display.
As well as attacking true lilies (Lilium), they will also attack fritillaries (Fritillaria) and giant lilies (Cardiocrinum).
The adult scarlet lily beetle is 6-8mm long with a black head and legs. The bright red wing coverings are easily spotted, but the insect has a cunning defence mechanism that makes physical capture difficult. When disturbed, it drops to ground level, turns upside down where its black underside is difficult to locate.
The grubs of this pest are even more sly, covering themselves with their wet, black excrement, which protects them from predator attack while they openly eat the lily leaves and flower buds.
The orange-red eggs are laid in clusters on the undersides of the leaves.
Treatment and control
Remove any adult scarlet lily beetles by hand and dispose of them. They are quite dosy early in the morning, so this is the best time to catch them. The larvae are disgusting to pick off, so remove a whole leaf where they are feeding and dispose of it.
Where this isn't feasible, or practical, then you can control them by spraying affected plants with an insecticide. The best ones to use are systemic insecticides. These are absorbed inside the plant and move all around the plant, killing the beetles and the grubs as they eat the leaves and providing protection against further attack for up to 3 or more weeks. Spray lilies as soon as the first grub or adult is spotted. A further treatment 3 weeks later will help to control any grubs that may have hatched from previously laid eggs.