Natural enemies
In parts of mainland Europe the lily beetle is kept in check by four species of parasitic (parasitoid) wasp that attack the larval stage, only one of which (Tetrastichus setifer) was known to occur in the UK. Research by the RHS found a second species of parasitic wasp (Lemophagus errabundus) in Britain in 1999. The continuing prevalence of this beetle as a pest would indicate that the parasitoids present in the UK are not sufficient to prevent the beetle causing problems.
Risk to lily growers
In 2006 the risk that the beetle poses to the lily-growing industry was assessed by surveys of end users (professional and amateur gardeners) and companies supplying lilies.
The surveys found that a quarter of those who had experienced a problem with the beetle, would reduce or stop growing lilies. It was also established that lilies grown under any regime, including under glass, are susceptible to damage. The primary conclusion was that the problem is likely to get worse as the beetle continues to spread throughout Britain. This is likely to result in increased insecticide use. However, despite many end-users of lilies stating they would stop growing lilies, lily suppliers indicated that sales have increased.
Odour-mediated behaviour
A major part of a recently completed PhD research project investigated the beetle’s odour-mediated behaviour. Such research is vital if the aim of developing a control of the beetle utilizing odours (volatile chemicals) to which the beetle responds to is to be developed.
Results from the experiments indicated that in the spring female beetles are able to locate lilies by odour alone, and that the beetles preferentially move towards the odour of plants already infested with other beetles. This part of the work was published in 2012 - Salisbury, A., Cook, S.M., Powell, W. & Hardie, J. 2012. Odour-mediated orientation behaviour of the lily beetle (Lilioceris lilii). Physiological Entomology 37:97-102
Control
At present gardeners rely on pesticides or hand picking to control this pest, but the long period over which the adults are active (late March to October), can make this difficult. Pesticides for use against lily beetle include those containing pyrethrum, deltamethrin, thiacloprid, imidacloprid or acetamiprid. Adequate control in areas where the pest is abundant may require measures to be repeated during spring and summer.