Invasive Alien Species in Northern Ireland

Lilioceris lilii, Lily Beetle

Lilioceris lilii
© Roy Anderson
Lilioceris lilii
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Lilioceris lilii (Scopoli, 1763), (Scopoli)
 
Introduction
The lily beetle is a small but attractive bright red leaf beetle (Family Chrysomelidae) which, until recently, was confined to southern counties of England. It feeds exclusively on plants belonging to the lily family (Liliaceae) including many garden varieties of lily (Lilium) and can be very destructive if left unchecked.
 
Description
The beetle is 6-8mm long and bright red except for the head, legs and antennae which are black. It can fly and presumably spreads from garden to garden in this way. The bright colours and its association with lily plants or fritillaries should serve to identify it. There are few other Irish beetles with such striking colouration. However, watch out for spotless forms of the 2-spot and 10-spot ladybirds which occur only rarely. These have an almost circular outline whereas the lily beetle is elongated and the elytra or wing cases are nearly parallel-sided.
Lily beetle larvae are much more difficult to identify and will be described under ‘Life cycle’.
 
Country of origin
The lily beetle occurs across the north Eurasian land mass from central Europe to the Pacific but is not native to the British Isles, where it has become established in historical times only, perhaps as late as the nineteenth century.
 
Current distribution
It was resident erratically in southern Britain for many years, beginning in the nineteenth century, but did not become permanently established until the 1940s. From this period on it was present in a few of the south-eastern counties of England. A serious northwards expansion appears to have occurred within the last twenty years or so. In a comparatively short time it has expanded north and west to cover most of central and southern England with scattered outlier populations as far north as Lancashire, but with only two sites in Wales. The expansion ties in with recent northwards movements by a variety of other insects, including some leaf beetles, which are thought to be responding to a warming of the climate in Europe and the British Isles. However, other forces are also at work. Since the end of the last glaciation, fauna in Europe has been moving, at varying rates, from strongholds in southern countries which escaped the glaciation, back to countries in northern Europe where they would have occurred before the glaciation. It is very difficult to know whether this natural northwards migration or something related to recent climate warming is occurring. In the case of the lily beetle, however, the timing suggests that climate change is the main, but perhaps not the only, factor.
 
Location in Ireland
The lily beetle is more or less confined to greater Belfast but has been spreading across south and east Belfast for several years and has currently (2006) reached Crossnacreevy about six miles into County Down (J3969). The first specimens were collected from a garden at Kings Road, east Belfast (J390734) on 5 June 2002. These were picked off an Asiatic hybrid lily, Lilium ‘Connecticut King’ by the home owner. He had seen red beetles on his plants in 2001 but had ignored them, so this was at least the second year of their occurrence at the site.
Not so far recorded in the Republic of Ireland but likely to be present.
 
Life cycle
Both adult beetles and their reddish brown larvae feed on the above ground parts of lilies. The adults are active from about late March until autumn. In spring they lay small groups of reddish-brown eggs from which the larvae emerge. The larvae cover themselves with wet excrement which dries forming a hard protective covering. They may feed in groups, eating leaves, usually from the tips back to the stem in spring and early summer. Damage increases through the summer and severe defoliation can occur. Plants may die but more usually the bulbs are under-sized and fail to flower the following year.
 
Wildlife and habitat impacts
There are few if any native Irish plants belonging to the Liliaceae which might be vulnerable to attack by the lily beetle. Lily of the valley and the fritillaries do not occur naturally in Ireland. Currently damage has been reported exclusively from garden plants.
 
Human impacts
This is a significant pest of cultivated lilies and their relatives in Britain. A very wide range of Liliaceae has been affected including, lily of the valley, May lily, Solomonís seal, day lily, giant lily, the lilies proper and the fritillaries.
It should be pointed out that many of these, though serving as food plants for the adults, are not used by the larvae. Species of Lilium are selected preferentially for egg-laying although larvae have been found one or twice on fritillaries.
 
Key vectors
The main method of spread is by bulbs infected with the larvae. Quarantine and disinfection of bulbs is the best method of preventing entry to new areas but depends upon co-operation from many different sources, including garden centres and nurseries.
 
What you can do as an individual
Members of the public have a role to play here by reporting suspected occurrences to CEDaR, Botany Department, Sciences Division, National Museums Northern Ireland, 153 Bangor Road, Cultra, Holywood, County Down BT18 0EU. Tel: 028 9039 5256, email cedar.info[at]nmni.com. Alternatively, they can report to their local garden centre staff or direct to the Royal Horticultural Society which is monitoring the problem.
 
Advice to specific groups relevant to this species
The Royal Horticultural Society at present recommends the removal of adults and larvae by hand. Adults are relatively easy to spot but the larvae are well camouflaged and may be overlooked, so that the treatment of affected plants with an insecticide is essential. The RHS recommend imidacloprid + sunflower oil (Bio Provado Ultimate Bug Killer).
 
Management measures
As with many other invasives, invasion of new countries takes the lily beetle away from its natural controls and checks. The parasites which control its numbers within its native range are often less adaptable and may be left behind as the lily beetle spreads. Knowledge of the parasites could turn out to be useful, however, if work were undertaken on a biological control programme. Biological control methods have not been investigated so far, although the larvae are known to be infected and killed by at least four species of tiny parasitic wasp in Europe.
 
Further information
Links
Gardening Which
Royal Horticultural Society
RHS Science report on Red Lily Beetle (pdf).
 
Literature
Anderson, R. and Bell, A.C. (2002). A first record of the lily beetle Lilioceris lilii (Scopoli) in Ireland (Chrysomelidae: Criocerinae). Coleopterist 11: 90.
Cox, M.L. (2001). The status of the Lily Beetle Lilioceris lilii (Scopoli, 1763) in Britain (Chrysomelidae: Criocerinae). Coleopterist 10: 5-20.
 
Text written by:
Dr Roy Anderson