Research

Red lily beetle

The red lily beetle ( Lilioceris lilii ) has become the lily growers' nemesis; the adults and larvae can devour a lily plant in a matter of days. The beetle has been the subject of a three-year PhD research degree project which has improved knowledge of the beetle's host range and the ways that it locates its host plants. The PhD was successfully completed in January 2008.

The study, which was jointly funded by the Royal Horticultural Society and the Horticultural Development Council, was prompted by the increasing spread of lily beetle across the UK and its devastation of host plants. In the current decade it has been consistently one of the top five enquired about pest problems to the RHS Members’ Advisory Service . In addition to investigations carried out at Wisley, laboratory work was carried out at Rothamsted Research in Harpenden, Hertfordshire, and the Silwood Park campus of Imperial College London in Ascot, Berkshire.

Download a comprehensive scientific literature review of the lily beetle (Adobe Acrobat pdf 552KB)

Description

The red lily beetle is an 8mm (about 1/4in) long bright red beetle with a black head and legs. Eggs are found on the underside of leaves in linear groups of up to 15. They are 1mm (about 1/16in) in length and bright orange when first laid but darken as they mature. The larvae have dirty orange-red bodies with black heads; they are rather rotund with a humped appearance. The larvae normally cover themselves with their own slimy black excreta and could be mistaken for birds' droppings. Fully grown larvae are 8-10mm (about 1/4in) in length. The pupal stage is in the soil.

Life cycle

Adults emerge from the soil from late March to May. They feed and lay their eggs on the underside of leaves of host plants from late April until early September. The eggs hatch after approximately a week. Beetle larvae can be found feeding on the foliage between May and the end of September. After two weeks, when the larvae are fully grown, they pupate in the soil. Two to three weeks later new adults emerge and complete the life cycle. Despite claims in some literature, this beetle has only one generation a year. The beetles overwinter as adults in sheltered places, often in the soil but not necessarily near lilies.

Host range

Both adults and larvae damage lilies ( Lilium and Cardiocrinum spp.) and fritillaries ( Fritillaria spp.) primarily by defoliation, but in heavy infestations the flowers, seed capsules and stems will also be eaten. Although adult beetles have been found on other plant species, only lilies and fritillaries are true hosts, on which eggs are laid and the larvae develop.

The lily beetle has been observed on 57 hybrid Lilium , 30 Lilium species, one Cardiocrinum species and five Fritillaria species. The scientific literature indicates that not all lilies are equally susceptible, although there has been no attempt to quantify these differences. As part of the PhD a field trial assessing six different lilies (one species and five hybrids) was carried out to assess the lilies susceptibility. Results from the first three years of the trial indicated that the species lily was less susceptible than the hybrids. The trial is continuing for at least one additional year before the results will be prepared for publication.

Distribution

The lily beetle is not a native species to the UK; it has been accidentally imported into Britain on several occasions. It was first noticed at the end of the 19th century, with a handful of short-lived infestations reported from England and Wales. However, it was not until 1939 that an established colony was discovered in a private garden at Chobham, Surrey, by the RHS’s first entomologist, George Fox Wilson.

By the late 1950s the beetle had become widespread in Surrey and was also found in Berkshire. Later, an analysis of records held by the RHS Entomology section up to 1989, and the results of an appeal for records of the beetle in the RHS magazine The Garden in 1990, indicated that the beetle's range had expanded into Hampshire, Middlesex, Wiltshire, Dorset, Hertfordshire and Oxfordshire. During the 1990s the beetle continued to be reported from new areas of England and Wales and by the end of 2007 this pest had been found in almost every English county. In 2002 the beetle was reported for the first time from Glasgow and Belfast. Continued reports to the RHS indicate that the beetle is now established in Scotland and Northern Ireland.

Distribution of the lily beetle in Britain and Ireland. From Records held by the RHS (at December 2007). Produced using DMAP©

Click here to submit a record of lily beetle

The lily beetle is native to Eurasia, although it is currently impossible to know exactly where. It is now found almost anywhere that lilies are grown, and has become established in North America where it is continuing to spread. More information

The increase in the distribution of lily beetle over the past two decades has been coupled with a rise in its frequency as an enquiry to the RHS Members' Advisory Service. Before 1980 lily beetle enquiries made up less than 1 percent of all pest enquiries received, but during the past two decades the proportion of enquiries has increased to more than 3 percent.