The red lily leaf beetle (Lilioceris lilli) can strip a lily of its leaves, stems, buds and flowers in as little as one to three days, leaving only a bare stem. Unable to regenerate its bulbs through photosynthesis, this feeding ultimately kills the plant.
Red lily leaf beetle also attacks Solomon’s seal, Fritillaria, Nicotiana and even hostas when there is nothing else left to eat, although it is selective about where it lays its eggs; only on Lilium and Fritillaria species.
These killers arrived in Canada via potted lilies as early as 1945, first making their appearance in Ontario and Quebec. They arrived in Manitoba almost a decade ago. As alien bugs, they have no natural predators here, so the main line of defense is diligence, keeping a wary eye out for the eggs, the larvae and the beetles.
The bright orange eggs are laid on the underside of lily leaves in uneven rows of two to 12. They look like little orange grains of rice. Each mature beetle will lay 200 to 450 eggs.
The eggs hatch in five to 10 days, entering the larval stage for another 16 to 24 days. At the beginning of this cycle, they feed on the underside of the leaf and their munching looks like leaf miner damage to the causal observer. Eventually, they move to the tips of the leaves, eating from the outside toward the stem. It is now that they cover themselves in excrement as a defense mechanism against predators. They look like slimy drips of bird lime.
At the end of this time, the larvae fall or crawl to the ground and burrow into the top half-inch or so of the soil to pupate in a self-spun cocoon, emerging as adults in 20 to 25 days. You can find the pupae if you examine the top layer of your soil near host plants — they are easy to spot being bright orange grubs, 1/4 to 3/8 inches long, with black heads (although some reports also mention that they can be green or yellowish as well).
After pupating, the beetles emerge as adults with shiny, bright red wings. The beetle is also a voracious feeder and can do much damage at this stage. They are very effective fliers.
At the end of the season, some adults hide under debris or just under the surface of the soil to begin the cycle all over again in the coming season.
Sevin and pyrethrin-based insecticides will kill lily leaf beetle larvae and the bugs on contact.
Neem will not instantly kill but will deter the adults from attacking lilies, so precautionary spraying is a good thing if you know the insects are in the neighbourhood. Neem’s advantage is that it works systemically. When a leaf treated with neem is ingested, the neem interferes with the reproductive process of the insect by blocking the hormone that governs metamorphosis. It can also interfere with the digestive process.
Spray plants with neem every five to seven days, being sure to cover all the parts as thoroughly as possible. Repeat the process for about three weeks to effectively interrupt the life cycle of new generations. Neem does not affect bees or birds. You can purchase neem on the Internet.
Meanwhile, hand-pick and kill any adults. Note that the lily-leaf beetle makes a chirping sound as an adult. You may find this disconcerting when squishing them, so be prepared. The adults will become inert when attacked and may play dead and fall to the ground, belly side up, which makes them hard to see when hand-picking.
If you don’t have neem and dislike using chemicals, you can carefully strip eggs from leaves using soapy water. Be sure to examine the ground for grubs. If squishing adults makes you squeamish, you can try knocking them into a pail of soapy
The red lily leaf beetle is a major scourge for lily gardeners, although the Canadian Food Inspection Agency, the government department responsible for insect control, does not consider it an economic threat. They may feel differently if it infests the fields of some of our important lily breeders, but by that time, it may be too late.
The beetle loves Asiatic lilies, but according to the University of Maine, some resistant lily varieties include Lilium henryi ‘Madame Butterfly’, Lilium speciosum ‘Uchida’, and Lilium ‘Black Beauty’.
Dorothy Dobbie is the publisher of the Manitoba Gardener magazine. She broadcasts a weekly radio show on CJNU 97.3 FM also available via live streaming. For Gardener subscriptions call 204-940-2700. localgardener.net