Posted: 28/06/2015 at 14:27
Life cycle, species preference and clustering behaviour:
RHS site [link removed because auto-formatting can't handle it]:
As part of RHS research, the susceptibility of six different lilies was assessed (one species and five hybrids). Results from the trial indicated that the species lily Lilium regale was less susceptible than the hybrids. The results from the trial have been published - [link removed becasue auto-formatting was cutting out a lot of text]
One variety of Lilium is currently advertised as lily beetle tolerant, Lilium ‘Defender Pink’
An RHS-HDC funded PhD research project 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.
A Canadian lily site [link removed because auto-formatting is spazzing out all over this post today]:
1. Over wintering adult beetles emerge in early spring from the surrounding soil to mate and lay 200 to 400 eggs on the underside of the leaves of the lily plant.
2. Eggs usually hatch in about 7-10 days. Emerging larvae will begin feeding on the underside of the leaves and then move to the top. This stage lasts for about 16-24 days. They will cover themselves with their own feces to discourage predators.
3. Larvae drop to the ground and pupate for about 20-25 days. Pupae cases are dark brown or black in color and very hard to find in the soil.
4. Emerging adults climb plants and feed until fall but do not normally mate or lay eggs until spring.
5. New adult beetles appear to swarm together and fly to seek out new locations during August to September.
6. Adults over winter in the surrounding soil or under plant debris. Some adults may survive over two seasons.
So if you gave away a clean bulb while it was totally dormant, rather than a spade-load of soil with the plant somewhere in the middle, you probably kept the beetles to yourself and rescued the lily from them.
I see a number of suggestions for dealing with these things, some involving making tea from tobacco (which means using nicotine itself rather than a neonicotinoid and will kill bees too), rhubarb leaves (which will kill all insects and any curious pet that licks it off the plant) or dog-strangling vine (Dear GOD!) or spraying the lilies with neem oil, sunflower oil or dilute vinegar. Another suggestion was to visit the local cafe, get their used coffee grounds and splat them around the base of each lily, because the beetles find lilies by smell and the coffee masks it.