Lily Beetle Info & Tips
The red lily leaf beetle (Lilioceris lilii) is an insect native to Europe and Asia which rapidly spread through New England from Eastern Massachusetts and which has been also been found in Northern New York State. The original infestation in New England was detected in 1992 in Cambridge, Massachusetts, although the beetle has been active in the Montreal, Canada, area since 1945.
If uncontrolled, the beetle will completely defoliate and ultimately kill all true lilies (Lilium species, such as Asiatic, Oriental, Easter, Tiger and Turk’s Cap lilies). It will also feed on Fritillaria species, and many other plants, although the primary targets are Lilium and Fritillaria species.
The adult beetle is bright scarlet red, with black legs, head, antennae and undersurface. It is 1/4" to 3/8" long and is a strong flyer. The beetle reportedly will squeak if squeezed gently (however, few gardeners are willing to be gentle to this beetle). The adult lays reddish-orange eggs which hatch into particularly unpleasant larvae, which look like 3/8" long slugs; colored orange, brown, yellow or green with black heads. The larvae cover themselves with their own excrement (known as a fecal shield) which apparently repels predators, including gardeners who are generally very reluctant to handle the larvae. The larvae eventually become fluorescent orange pupae.
The adult beetle overwinters in the soil or plant debris and emerges in early spring looking for food and a mate. After mating, the female lays eggs in lines on the underside of Lilium or Fritillaria leaves. Some damage is done by the adults at this time, but the major damage comes when the eggs hatch into larvae in 7-10 days. The larvae voraciously consume all leaves within reach and may then start on flower buds. This continues for 2 to 3 weeks, when the larvae then drop into the soil and begin to pupate. In another 2 to 3 weeks the adult beetles emerge to start eating again. This process occurs from early spring to mid-summer. Reportedly the beetles won’t mate and lay eggs until the next spring.
If you suspect the beetles may be lurking around your lilies but you don't see any, carefully dig in the top half inch of the soil - no deeper! They hide just under the surface, so be ready to get them when they pop out.
There are no known natural predators in this country, although the beetle is well under control in Europe, where at least six parasitoids attack it. Researchers at the University of Rhode Island are actively engaged in releasing parasitic wasps in this country and seem to be confident that biological control can eventually be established here as well.
First of all, if you’re in an infested area, avoid sending any lilies or other plants to anyone else, and carefully inspect any plants you receive.
- Hand-picking should be the first level of control if possible. Constant vigilance and quick removal and disposal of beetles, eggs and larvae can control an infestation on a small number of plants. Make sure the critters are actually dead! If you squash them, don't leave the squashee in the garden. Some gardeners drop them into a can of water with vegetable oil on the top. Please note: The adults are easily spooked when you try to pick them by hand, and if you miss them, they tend to drop to the ground where THEY LAND UPSIDE DOWN, and since their tummies are black, they effectively vanish. A suggestion is to place a light-colored cloth under the plant before you hand-pick in order to be able to see them if they fall.
- Neem: If hand-picking isn’t feasible, then treatment with Neem is the next choice. Neem will repel beetles and kill young larvae, but must be applied every 5 to 7 days after the eggs hatch.
- Merit (imidacloprid) is a systemic insecticide which may work if applied to the soil in early spring. Many New England gardeners are also reporting good results from the use of products containing imidacloprid when applied later in the season. Bayer manufactures several products containing systemic insecticides, both in spray and in granular form.
- Other chemicals of relatively low toxicity include the following:
- 10% household ammonia applied to the newly emerging lily sprouts and surrounding soil (reported by northerner on of Ontario, Canada).
- Pyrethroid insecticides (Permethrin is one) kill adult beetles (reported by the UMass Extension).
- Spinosad insecticides kill larvae (reported by the UMass Extension).