Susceptibility of six Lilium to damage by the lily beetle, Lilioceris lilii (Coleoptera: Chrysomelidae)

The lily beetle (Lilioceris lilii, Chrysomelidae) feeds on Lilium, Fritillaria and Cardiocrinum plants and is a serious pest in gardens and amenity plantings in parts of Northern Europe and North America. Previous studies have indicated that within the beetle's host range there is variation in susceptibility, although thorough field investigation is lacking. Therefore a 3-year field trial was carried out to assess the susceptibility of six different Lilium to the beetle. The trial was laid out over two replicate blocks, with each block divided into a six by six grid, giving 36 plots; each plot contained nine Lilium of the same type. Lily types were allocated to plots within a block according to a quasi-complete Latin square. The plots were assessed weekly during the growing season over 3 years for plant damage and presence of the beetle. For each plot a damage index for each year was calculated as the average damage score per scoring visit. As beetle presence was low in the first year the damage index, mean adult, larval and egg presence over the final 2 years were analysed using ANOVA. The results indicate that there are significant differences in beetle occurrence and damage on the different Lilium in the trial, however there is also an interaction between damage index and year. The species L. regale and L. 'Golden Joy' gave consistently lower damage index/occurrence means than the hybrids L. 'Tiber', L. 'Brindisi', L. 'Conca d'Or' and L. 'Eliganzer'. We suggest that future host susceptibility trials should use a standard lily such as L. regale against which others can be compared, should take measurements of both beetle occurrence and damage and be carried out over several years to get reliable results. As there are differences in susceptibility of lilies there is a possibility to use lilies more prone to attack; this could be as trap plants for the beetle.