Plants affected
Lilies (Lilium species and hybrids) and fritillaries (Fritillaria species)
Symptoms
Holes first appear in the foliage in the spring and early summer. Damage increases through the summer and severe defoliation can occur. Because of this, the bulbs become under-sized and may not flower the following year. It is important to prevent serious defoliation happening before the end of flowering in order to allow next year's bulbs to bulk up.
Cause
Both the bright red beetles, 6-8mm long, with black head and legs, and their reddish brown grubs feed on the above ground parts of their host plants. The adults are active from late March or April to autumn. In spring they begin laying small groups of reddish brown eggs on the underside of the leaves. The grubs are rotund, soft-bodied reddish-brown grubs with black heads. They are hidden under a covering of their own wet, black excrement and often feed in groups, eating the leaves from the tips back to the stem. There is one generation a year.
Originally confined to south east England, scarlet lily beetle has now spread to all counties in England and some parts of Wales. In 2002 it was found for the first time in Scotland at Glasgow and in Northern Ireland at Belfast. It is becoming more widespread in both of those countries.
Control
Inspect plants regularly, and pick off and destroy any adults, eggs or grubs when seen.
Infested plants can be sprayed with imidacloprid + sunflower oil (Bayer Provado Ultimate Bug Killer concentrate), acetamiprid (Scotts Bug Clear Ultra concentrate) or thiacloprid (Provado Ultimate Bug Killer Ready To Use). The larvae are more susceptible to insecticides than the adults.
Further information
Current research at the RHS Garden Wisley into scarlet lily beetle.