Asian Lily Beetles – A New Garden Threat

Anyone genuinely interested in Nature – while perhaps naive enough to believe in its absolute innocence – might think the small, bright fiery-orange beetle that’s suddenly materialized in their gardens is strikingly beautiful and perfectly harmless. About the size of a rather narrow ladybug without spots, it almost sparkles as it seems to sun itself on the leaves and emerging flower buds of Asiatic and Oriental hybrid lilies.

In fact, the appearance of innocence and beauty is totally misleading…if not downright deceptive. Early spring sunbathing is clearly not what it has in mind! Lilioceris lilii. Asian Lily Beetle, aka Lily Leaf Beetle, is focusing its entire attention on filling its belly and finding a mate. When those two primary goals have been fulfilled, watch out! Your beautiful lilies are about to vanish. And if you have no hybrid lilies but concentrate on growing fruits and vegetables, your tomatoes, potatoes, eggplants and peppers (nightshades) are in serious jeopardy.

Where did they come from? Asian Lily Beetles first appeared in Boston a little over a dozen years ago, probably stowaways in plants imported from abroad…quite possibly China. Rapidly spreading throughout Massachusetts and points north, by 1999 they had worked their way up the New England coast to Brunswick, then inland areas…finally reaching the Mid-Coast and more than a few miles inland to the west, devastating lilies as they traveled. Now they have occupied very nearly every agricultural and horticultural area in several eastern states and three Canadian provinces and, in my opinion – and that of a great many other horticultural/entomological professionals – will soon surpass the populations and crop damage done by the dreaded Japanese Beetles (Popillia japonica).

Adult Lily Leaf Beetles over-winter in the soil or in un-cleaned-up plant debris after fall frost. Following emergence during early spring, they mate and quickly deposit between 200 and 300 tiny dull-orange eggs on the undersides of leaves, in clusters of two to ten. Hatch occurs in five to ten days after which larvae feed for between 16 and 24 days, growing rapidly to about twice the size of their parents. It is at this point that they are feeding heavily. Highly vulnerable to predacious insects during this “soft” feeding stage, larvae cover themselves in their own sticky, mud-like excrement (droppings) as a highly effective defense against attack. Most gardeners describe them as looking like small dirty slugs. If you scrape the feces away, you’ll see a soft, dull-red beetle whose wing cases have as yet to harden.

At about this point, larvae either crawl or drop to the ground where they pupate in secreted cocoons. In under 25 days, a fully mature adult emerges to begin the process anew. There can be as many as three such generations in a single season. To make matters worse, it is possible for female beetles who have deposited their eggs for the current season to survive a second winter and lay another huge clutch of eggs the following year. Allow me to do the math for you: One mature female beetle x 200 x 200 x 200 = 8,000,000 at a minimum. And that’s in our short New England growing season. Alfred Hitchcock would’ve had a field day with those numbers!

What else will they attack? An all-time dietary favorite is fritillary (Fritillaria sp.), but are most often seen on Asiatic, Oriental, and “tiger” lilies (Lilium sp.), lily of the valley (Convallaria majalis), Solomon’s seal (Polygonatum multiflorum), certain vegetables, and occasionally other common garden perennials when their favorites are either not present or already consumed.

How are they controlled? Best of all is daily scouting of your garden, hand-picking or knocking adults into a jar of soapy water, or spraying with one of the products described below. There are two natural “pesticides” effective in the control of Asian Lily Beetles:

1. NEEM, a biochemical pest control substance extracted from the tropical Neem tree. It affects the insect while in its larval stage by interrupting molting, and may also serve to repel adults.

2. PYRETHRIN, a product extracted from common painted daisies (Pyrethrum sp.), may be sprayed on plants to control both adults and larval stages. I consider Pyrethrin to be the best choice.

I have also noted that RESMETHRIN – a synthetic form of Pyrethrin found in formulations for garden foggers – destroys the larval form.

All of these insecticides are commonly stocked by large, retail garden centers, and less reliably at “big-box” stores. As always, read and observe all labeling information. Wear protective gloves when handling or applying, and wash thoroughly when the job’s done. Even though they’re considered “natural”, there’s no point in taking any chances with your health or that of your loved ones.

One last thought: The true key to controlling population numbers of this new and highly destructive villain in your garden, in the words of Alistair “Mad-Eye” Moody of Harry Potter fame: CONSTANT VIGILANCE! We must be ruthless and unyielding in our search for and destruction of every Asian Lily Beetle we encounter! The future of hybrid and tiger lilies in our gardens depends on it.