Lily leaf beetle

Jul 21, 2011

By Lanark County Master Gardeners 

Lily leaf beetles make noise by rubbing two body parts together when they are threatened. Just as their name suggests, their foods are lilies and fritillarias. Even their scientific name, “Lilioceris lilii” tells us the plants they feed on. They do not feed on daylilies or other plants with lily-like names.

They have four stages to their life cycle: egg, larvae, pupa and adult. These insects over-winter in the adult stage as a beetle. They are bright red on top, less than half an inch long ( 6-9 mm.) and an eighth of an inch (3mm.) wide. Their head, antennae and underside are pitch black. One of the defense mechanisms (thanatosis) is to fold up its appendages and fall to the ground with its black underside facing up. Expecting to see a bright red beetle on the ground they become very difficult to find. These beetles emerge in the spring from the soil or plant debris just in time to begin feeding on the leaves of lilies. Pick the adults and crush them before they have a chance to lay their eggs. Irregular bands of small orangey eggs are laid on the underside of leaves. Squish them by rubbing your finger over them making sure to get every last one. The eggs hatch in six days and the larvae start to feed for twenty-four days on the underside of the leaf, sometimes defoliating the entire plant. This is the most destructive stage. While they eat and grow, the larvae cover themselves in their own frass. Again pick off the larvae and when you have several in the palm of your hand squeeze them until they are oozing from between your fingers. They are orange with the black frass covering. The larvae fall to the ground when mature where they pupate and emerge as the red beetle in about twenty days. There could be more than one life cycle in a growing season.

They feed on the underside of the leaves, so chemical control is difficult as most gardeners cannot be bothered to spray under the leaves. Nowadays there are practically no chemicals available except neem oil. Apply it every five to seven days. Hand-picking the adults and squishing the eggs and larvae as you see them is by far the most effective. There are no natural predators. Enjoy your lilies.

Submit your gardening questions to our website www.lanarkmastergardeners.mgoi.ca for responses by a master gardener.