Garden pest control - Red Lily Beetle (Description and control instructions)

Scientific name: Lilioceris lilii
Other Names: Scarlet Lily Beetle, Lily Leaf Beetle or Asiatic Lily Beetle

The two adults shown above were found in the mulch at the base of an old lily stalk when doing some autumn tidying, and were probably settling in for the winter.

The bright red body, black legs and head make Lily Beetles very striking in appearance, but these little beasts are very destructive to bulbous plants and in particular Lilium such as Turk's cap lilies, Asiatic lilies, Oriental lilies, Tiger lilies and some Fritillaria species. From spring to autumn the adults and larvae feed on the foliage, flowers and stems. The removal of the leaves deprives the plant of food production which severely weakens it and may prevent flowering the following year, or in severe cases kill the plant.

The Lily Beetle is native to mainland Europe and Asia, but not the British Isles. First reported in Southern England in the nineteenth century, it is believed that they did not become established until the 1940s. They had been confined to the south, but the recent increase in average temperatures has allowed them to move northward, and the specimens pictured here were found in a garden near Newtownards, County Down in October 2006 - the first reported find in Northern Ireland was in a garden in Belfast in June 2002.

They have also moved to North America, first reported in Canada in 1945 and now spreading south in the eastern states of USA.

In the spring the adults climb out of the soil and after mating the female lays her bright orange eggs in lines under the leaves of Lily plants or Fritillaries. The orange larvae emerge after 7 to 10 days and begin feeding - first instars from underneath and later ones eat through the foliage, working from the tip to the stem. They cover themselves with their sticky black excrement to act as a deterrent to predators, so the orange colour disappears and they are more difficult to spot. The larvae cause most of the damage and spend two to three weeks stripping the foliage, then the flower buds before dropping to the ground to pupate. After two to three weeks the bright orange pupae have metamorphosed into new adults which climb into the plants to continue the cycle. Mating can occur from spring until autumn and surviving adults move to the ground to spend the winter.

The adults have been found on other plants including Lily of the Valley, Soloman's seal and Day Lilies. The larvae have only been found on bulbous Lilies and Fritillaries.

Treatments

• The recommended method of removal is to check affected plants regularly picking off and crushing any adults, eggs or larvae. The adults tend to drop to the ground with their black undersides showing when the plant is disturbed so they are easier to find if a light-coloured material is placed there first.
  
  
• Due to the difficulty in spotting the larvae a follow-up treatment with an insecticide is advisable - one containing Imidacloprid such as Bio Provado Ultimate Bug Killer (Imidacloprid and Sunflower Oil) - UK, Merit - USA.
  
  
• As a preventative the insecticide can be applied to the soil in the spring to eliminate the overwintering adults before the lilies start into growth.
  
  
• A more "friendly" insecticide made from extracts of the Neem tree is also effective when applied to the early stages of larvae. It kills them and deters the adults. There are no biological controls, but they are attacked by parasites in their native areas. Some research has been done with a parasitic wasp.
  
  
• There are a few preventative measures which can be taken, such as checking new bulbs for larvae before planting. Probably the most likely method of spread is the recent trend of buying established lilies in pots.
  
  
• It used to be that we bought bulbs and planted them, but the marketing of "added value" products means that the horticulture industry can make more money by potting them for us. They are grown in warmer places in close proximity to each other so the pests have a better chance to thrive. So check any such purchases carefully before introducing them to your garden.