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Asian Lily Beetles (aka "Lily Leaf Beetles")
by Fred Davis, MG, Hill Gardens of Maine
(To view other articles, click Archives)

 

    Welcome through Fred's Garden Gate!  Anyone really 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 stunningly beautiful and perfectly harmless. The Asian Lily Beetle and its eggs. 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 certainly 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 focus 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 Cambridge during the summer of 1992, said by some authorities to have spread there from Montreal. More than a few New England gardeners believe the insects arrived with bulbs imported from Europe. 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. 

    Adult beetles over-winter in the soil or in un-cleaned-up plant debris after fall frost. After emerging in early spring, they mate and quickly deposit approximately 200 tiny dull-orange (quickly turning to brown) eggs on the undersides of leaves, in clusters of two to ten.Asian Lily Beetle covered with its own excrement. Hatch occurs in five to ten days after which the larvae feed for between 16 and 24 days, growing rapidly to about twice the size of their parents. It's 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 very 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.

Click image for enlarged view    At 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 3 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. Here's the math: 1 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!

Click image for enlarged view    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 three natural "pesticides" that are effective in the control of Asian Lily Beetles:

  1. NEEM, a biochemical pesticide that is 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.

  3. ROTENONE has also shown to be effective against adults and larvae. It can be applied either as a spray or, on a calm day, as dust.

   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 all 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.

 
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