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Lily Leaf Beetle

Ravageurs et maladies
English
Lily Leaf Beetle.
Photo: Jardin botanique de Montréal (Pascale Maynard)
Lilioceris lilii
  • Lilioceris lilii
  • Lilioceris lilii

Onglets

Description

Summary

These pretty little red beetles, introduced from Europe, can cause enormous damage, primarily to lilies. They are easy to spot, but more difficult to trap, because as soon as they sense danger they play dead and drop to the soil. An uncontrolled infestation can quickly defoliate a plant.

Signs and symptoms

  • The first signs of damage appear in early spring, when the adults emerge from the soil and chew on newly forming leaves.
  • The yellow, red or orangish eggs are laid in strips on the underside of young leaves.
  • The larvae are sheltered in a blackish layer of mucus and excrement. At first they feed near the sites where the eggs were laid, generally on the underside of leaves.
  • After eating all the foliage, the adults and larvae chew on the flower buds and flowers.
  • In a severe infestation, the entire plant may be devoured, but the bulb is usually spared.

Latin name (genus)

Lilioceris lilii

Host plants

Primarily lilies and fritillaries; sometimes Solomon's seal and other related species.

Name of host plants

Development cycle

Description and life cycle

Lily leaf beetles are tiny insects belonging to the order Coleoptera. They undergo complete metamorphosis (holometabolic insects). Before reaching adulthood, they pass through the egg, larva and pupa stage.

Eggs: They are yellow, orangish or red, with an elongated capsule shape, about 1.5 mm long.

Larvae: They have a yellow body with black head and legs. They are about 9 mm long at maturity. They hide from predators under a blackish mass of mucus and excrement.

Adults: They are between 6 and 8 mm long. They have a bright red body, and their legs and pair of antennae are black.

Lily leaf beetles overwinter buried in the soil, as adults, often at the base of their favourite plants. They appear in early spring (April), to feed on the young emerging foliage and to mate.

Each female lays about three hundred eggs, attaching them in bands on the underside of young leaves. The eggs hatch after a week or two, and the newly hatched larvae feed on the plants for a few weeks. After that, they drop to the ground or descend the plant stem, and burrow into the soil to pupate, emerging as adults 4 to 5 weeks later.

The new generation of insects appears in late June or early July. The adults start seeking shelter for the winter in late July. In our climate, lily leaf beetles generally produce a single generation each year.

Prevention and control

Favourable conditions

Populations tend to swell after mild, snowy winters.

Identification

In early spring, inspect all susceptible plants regularly to prevent damage.

Prevention

  • Avoid planting susceptible plants, especially when lily leaf beetles are present.
  • When buying lilies or other host plants, carefully examine the underside of foliage to identify any eggs or larvae; check for insects on the plant or in the soil to avoid introducing any intruders.

Physical control

  • In spring, cover young plants with a floating row cover (fabric that allows light and water to penetrate) to prevent the adults from feeding and laying their eggs on the plants.
  • Crush any eggs you find on the underside of leaves.
  • Crush larvae and adults or drown them in a bucket of soapy water. To make it easier to trap the adults, you can shake the plants over a piece of fabric or a container. You can also pick them off with a small vacuum.
  • In fall, rake up plant litter and dead plants from the soil, where the adults could be hiding.
  • In spring and fall, rake the soil around plants to expose the insects to predators and severe weather.

Biological control

None available.

Chemical control

The Montréal Botanical Garden does not recommend the use of pesticides to control these insect pests.

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