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10 Neat Things About Lily Leaf Beetles

By Donna Dawson
7/18/2013 11:26:14 AM

It's Lily Leaf Beetle season.

1. Scarlet menace.

Lily growers despise the red or scarlet lily leaf beetle, Liliocerous lilii. Originally from Asia and Europe, beetles finally immigrated to Canada where they were first detected in Montreal in about 1943. They have been terrorizing Eastern gardeners ever since. Now they are steadily marching westward, where they have been reported as far west as in gardens around Calgary. (I saw and photographed them in one garden there.) Both larvae and adults feed on lily leaves and will strip the plant in no time, leaving it weak and unable to photosynthesize and feed its bulbs.

2. True lilies and fritillaries beware.

These scarlet beetles are attractive as adults with a shiny red cape. Don't be fooled by their fourth stage, when they look like ladybugs without the spots. The red lily leaf beetle loves all members of the lilium species. It ignores the daylily (Hemerocallis), but if it runs out of food it will eventually attack other plants, such as Solomon's seal, hosta, hollyhock, potatoes and bittersweet - and who knows what else!

3. When do they become active?

Adult beetles spend winter just under the soil or under plant debris, usually where lilies grow; however, they can also decide to do this quite a distance away. They emerge in early spring, to feed and mate. They attack young lilies then lay their eggs in about May. One gardener suggests drenching the soil and spraying young lilies with a 10 percent ammonia solution as a preventative.

Credit: ICanGarden

4. How many eggs can one beetle lay?

Each female lily leaf beetle will lay between 250 and 450 eggs in a season. They cover the eggs with a brown, sticky adhesive to keep them attached to the leaf. They lay about 12 eggs per leaf, along the ribs on the underside of the leaf. Watch for tan colored eggs, which will turn orange, then bright red just before they hatch. Eggs hatch in four to eight days. Squish them.

5. Larvae look like bird droppings.

Larvae protect themselves with their own excrement (worm poop is called "frass") and look like slimy bird droppings while they feed voraciously on your lilies. Squish them, too, because they feed for 16 to 24 days before turning into mating and egg-laying adults.

6. Not everything is turned off by worm poop.

The only thing that really works against the lily leaf beetle is a host of parasites. About a half dozen have been identified and are being tested in the U.S. Fortunately, the excrement trick only discourages birds and people, but not the parasitical wasps that attack the larvae.

7. Sleeping in slime and soil.

When they are ready to enter the next phase of their lives, the beetles burrow into the soil and pupate in a saliva and soil cocoon. They stay there for 20 days then emerge as adults and begin feeding all over again. They keep this up until winter.

8. Thanatosis and stridulation.

To protect themselves, the beetles will play dead, folding up their legs and antennae and falling upside down on the ground so they are hard to see. That's called thanatosis. Another trick is to squeak to startle predators. They do this by rubbing body parts. That's called stridulation.

9. The killing fields.

Okay, to get to the point, here's what you can do. Squish! Yes, handpicking is the best line of defense for those who have smaller lily patches. For bigger problems, there is a whole menu of choices. Neem oil works on contact with eggs and larva. It needs to be applied every five to seven days. And it does deliver a deterrent effect. It is safe for humans and bees. Malathion (it kills bees) and Rotenone will kill adults. So, apparently, will pyrethrums. Professional growers can use floating row covers to keep adults from feeding and laying eggs. Imidacloprid (sold under the name Marathon) is a nicotine-based systemic insecticide, which acts as a neurotoxin. There are questions about its effect on honeybees. Spinosads are microbial, but are, again, toxic to bees and not proven effective..

10. The final solution.

Parasitic wasps have had the best control effect. Too bad they hadn't yet learned of this is Nova Scotia, where they grew about 50 species of lily in 1996 and only one by 2006 due to the scarlet lily leaf beetle.

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