What is red lily beetle?

Lily beetle and its larvae are leaf-eating insects of lilies and fritillaries. The adult beetles are very occasionally found on other plants but lilies and fritillaries are the only plants on which eggs are laid and the grubs develop. Apart from spoiling the plants' appearance, attacks in early summer can result in undersized bulbs developing, which may not flower next year. Lily beetle has become widespread in Britain and Ireland since the early 1990s.

Survey

Seen the lily beetle? We would like to know.

As part of RHS research we would like to know where the lily beetle has been seen.

Please submit your records via our lily beetle survey (expected time to complete survey = two minutes).

Submissions to our pest and disease surveys are stored permanently in an anonymised form in order to monitor the spread of the pest or disease.  We may contact you within 2 months of your submission in order to verify your sighting but your personal data will not be permanently stored in connection with your submission and will be deleted after 1 year. We publish and share only non-identifiable data from survey submissions (such as a six figure grid reference) with third parties and the public for the purposes of scientific research and advancing understanding among gardeners.

Thank you to everyone who has submitted records – read a blog about the surveys

Symptoms

Gardeners should look out for;

• Adult beetles which are 8mm long and have bright red wing cases and thorax. The head and legs are black
• Clusters of orange-red, sausage-shaped eggs on the undersides of leaves
• Larvae which reach 6-8mm long and are rotund, reddish brown with black heads. They are usually completely hidden under their own wet black excrement (insect excrement is known as frass)
• Young larvae graze away the underside of leaves, resulting in white or brown dried up patches. The older larvae eat entire leaves, starting at the tips and working back to the stem, they will also feed on petals, stem and seed pods 
• Adult beetles make rounded holes in the leaves and will also feed on petals and seed pods

Control

Lilies and fritillaries can tolerate some damage from this insect. However in come cases the plants can be stripped of all foliage which can affect the health of the bulb. The adult beetles overwinter away from host plants and so there is no suitable treatment outside of the growing season.

Check lilies and fritilaries frequently from early spring onwards so action can be taken before a damaging population has developed. When choosing control options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section. If this is not sufficient to reduce the damage to acceptable levels then you may choose to use pesticides. Within this group the shorter persistence pesticides (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife than those with longer persistence and/or systemic action.

Non-pesticide control

• Where possible tolerate populations of beetles
• Remove beetles by hand where practical
• Encourage wildlife in the garden, such as birds, frogs, wasps and predatory ground beetles who will eat the larvae and sometimes the adult beetles
• The lily 'Defender Pink' is advertised as lily beetle tolerant
• One product is sold as a repellent against lily beetle, Grazers G4

Pesticide control

• Pesticides are likely to be more effective on larvae than adults. Adults can also fly in from adjacent gardens
• Organic contact insecticides containing natural pyrethrins (e.g. Bug Clear Gun for Fruit & Veg, Neudorff Bug Free Bug and Larvae Killer). Several applications of these short persistence products may be necessary to give good control
• More persistent contact insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer) and cypermethrin (e.g. Py Bug Killer)
• The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available

Follow label instructions when using pesticides. Plants in flower should not be sprayed due to the danger to bees and other pollinating insects. Inclusion of a pesticide product does not indicate a recommendation or endorsement by RHS Gardening Advice. It is a list of products currently available to the home gardener.

Download

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biology

Red lily beetle overwinters as adult beetles in soil, leaf litter and other sheltered places. This could be anywhere, not necessarily in the vicinity of lilies and fritillaries. Consequently, there is no advantage in attempting to treat the soil below lily plants. The beetles begin emerging on sunny days in late March and April when they seek out the foliage of host plants.

Eggs are laid in small batches on the underside of leaves during April to mid-summer. The eggs hatch and the larvae feed on the foliage. When fully fed, the larvae go into the soil to pupate. The next generation of adult beetles emerges from mid-summer onwards. These beetles add to the feeding damage but there is only one generation a year and these late summer adults will not mate and lay eggs until the following year.