The adult red lily beetle is a voracious pest of lilies and can literally destroy a gardener's ability to grow this plant almost overnight (at least that's how fast it seems).
Here's how to identify the pest (see pictures) although if you see a relly bright red beetle on your lily, it is pretty hard to miss what it is.
The adult red lily beetle is an 8mm long, bright-red beetle with black head and legs.
The beetle larvae have dirty orange-red bodies with black heads; they are more rounded than the beetle. The larvae could be mistaken for bird droppings (nice hiding technique) as they cover themselves with their own slimy black excreta. As long as they get adequate food, (lilies) they'll get get to 8-10mm long and then they drop off the lily to pupate in the soil.
Both adults and larvae eat lily (Lilium and Cardiocrinum spp.) and fritillaries (Fritillaria spp.) leaves but in heavy infestations they'll eat it all - flowers, seed capsules and stems will be eaten to the ground.
You might find them on other plants but they're only visiting. They only eat the two plants above and they only breed on them as well.
This pest will be a problem from early spring until late fall unless they are controlled.
Adults emerge from the soil in April and May to begin feeding on lily leaves. About four weeks after emergence, they lay their eggs on the underside of lily leaves. The eggs hatch after seven days. The emerged beetle larvae take about two weeks to grow up and then they drop to the soil to pupate. Two to three weeks after that, the adults emerge, begin feeding again and complete the life cycle. Only one generation is produced in a season.
The red lily beetles overwinter as adults in sheltered places, often in the soil or under layers of mulch at the base of lily plants.
Predators: In parts of mainland Europe the red lily beetle is kept in check by four species of parasitic wasp that attack the larval stage. These have yet to be imported to N.A.
Organic gardeners will usually do several things:
Hand-pick the beetles. Drown them in soapy water (the water has to be soapy so the beetles don't just swim and crawl out) If you get all the red lily beetles in the early spring when they first emerge from the ground, you'll not see too many more problems the rest of the summer. If you miss picking them, your lilies will be eaten to the ground.
Use diatomaceous earth. This powder is reputed to work on the red lily beetle by giving it lots of tiny cuts and the insect dies from dehydration.
Neem oil is said to be quite effective when it hits the red lily beetle. Note that it MUST be reapplied regularly as water (dew or rain) will wash it off the leaves. it acts more as a deterrent than a kill but that still works. :-)
Soapy water does NOT work – you only have a clean red lily beetle.