Unfortunately, lily beetles are long lived as insects go, so you’ll need to check for eggs until sometime in July, depending on the weather.
Several of you have written to me about hand-picking adults off your plants. While this is a useful thing to do, remember to check the plants for the orange eggs. Although this is time consuming, the eggs can be easily squished, and squishing eggs now sure beats removing the horrid larvae in a couple of weeks!
Unfortunately, lily beetles are long lived as insects go, so you’ll need to check for eggs until sometime in July, depending on the weather.
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After an exceptionally late start to spring, gardeners in eastern Ontario are finally enjoying some perfect spring weather. Lilies are starting to sprout and the beetles are are emerging from their winter hiding places. A.B. from Ottawa sent the photo above, and explains that the beetles are hammering her lilies, which are still only a couple inches tall. I planted some lily bulbs on Sunday, in my tiny backyard garden. We moved in last summer, and there were no lilies in the garden, which the neighbours tell me had been neglected and overrun with weeds for the last few years. Yet despite the fact that the lilies I planted are nothing but tiny white nubs that had sprouted in the peat moss the bulbs had been packaged in, by this morning they had been colonized by the red menace. The beetles are out in our experimental gardens too, where they will find refuge from all the local gardeners who would like to squish them. These lucky beetles will be pampered. We need them to produce plenty of offspring to provide hosts for the parasitic wasps we will release later this summer: Tetrastichus setifer and Lemophagus errabundus.
At home though, I will be merciless…. The lily leaf beetle is not the only bright red Lilioceris beetle in North America. The beetle pictured here is Lilioceris cheni, the air potato leaf beetle. Like the lily beetle, the air potato beetle is an exotic insect introduced to North America, but unlike the lily beetle, this introduction was intentional. The air potato beetle is a biological control agent that was introduced in 2012 from China to combat air potato in Florida. It’s one of the good guys. Air potato is a fast growing vine in the yam family (Dioscoreaceae) that has been spreading throughout Florida since the early 1900’s when it was introduced from Asia as an ornamental. The picture below, taken in March before the vines start to sprout, shows a potato or “bulbil” (red arrow) hanging from last year’s withered vine up in an oak tree. The bulbils drop to the ground and sprout, resulting in dense monocultures that smother native vegetation. Like all biological control agents, the air potato beetle was subjected to rigorous testing to ensure that it would not eat native plants or crops once released. A second Lilioceris species, which eats the bulbils rather than the leaves of air potato, is also being considered for release (photo below). It is currently in quarantine at the USDA/ARS Invasive Plant Research Laboratory in Fort Lauderdale, where it is being tested on a wide variety of plants to make sure that it is safe to release. For the time being, the lily leaf beetle and the air potato beetle are separated geographically by at least 1000 km*. However, as the lily beetle extends its range southward and as air potato moves northward, the distributions of the beetles might someday overlap. When this happens, will our biological control agents, the wasps Tetrastichus setifer and Lemophagus errabundus, attack the beneficial air potato beetle?
* but we could be wrong--help us update the lily beetle's geographic distribution by reporting an infestation! This photo shows a lily leaf beetle eating a plant that lily aficionados will immediately realize is definitely not a lily. It is Solanum dulcamara, climbing nightshade, a plant in the same genus as tomatoes, potatoes and eggplants. It is easy to understand that lily leaf beetles attack plants that are closely related to lilies, such as fritillarias. But nightshade is not at all closely related to lilies. The evolutionary lineages leading to the genus Solanum on the one hand and the genus Lilium on the other split from each other back in the Jurassic Period, when dinosaurs dominated Earth’s fauna. This deep evolutionary separation would lead us to expect that lilies and nightshade would be fundamentally different—and they are in many ways. So why does climbing nightshade attract lily beetles? Despite the evolutionary distance between lilies and nightshade, there are similarities in the chemical compounds they use to defend themselves from herbivores. Nightshade belongs to a plant family, the Solanaceae, that is characterized by potent alkaloid chemicals, such as nicotine in the tobacco plant Nicotiana tabaccum. Although lilies are less well known for their toxicity, many contain steroidal glycoalkaloids, just like plants in the genus Solanum. Apparently this chemical similarity is enough to entice lily beetle adults to feed on nightshade.
Even the most toxic plants have at least a few herbivores that have evolved the metabolic capacity to detoxify their host plant’s potent chemicals. The herbivores often use the chemicals as cues to find their host plants. Many of these herbivores then use their host plant’s chemicals to defend themselves against their own natural enemies. A relative of the lily leaf beetle, the three lined potato beetle Lema trilinea, feeds on nightshade, and the larvae incorporate the plant’s alkaloids into the fecal shields they hold over their backs to ward off predators. Their alkaloid-laden fecal shields effectively defend them against generalist predators, such as ants. However, specialized parasitic wasps will often use the plant chemicals in the shields as a cue to find the larvae. Lemophagus pulcher, the wasp we have petitioned to release next summer, is attracted by the lily-chemical odor of lily beetle fecal shields. When a pest herbivore incorporates a new host plant into its diet there can be important consequences for biological control. Feeding on a new host plant can provide a refuge where the herbivore cannot be found by its parasitic wasps, because the wasps rely on the visual or chemical cues of the normal host plant to find the herbivore. A good example of this is provided by the diamondback moth Plutella xylostella, an important pest of crops in the cabbage family. The diamondback moth has recently moved onto snowpeas in Africa, where it is relatively safe from the parasitic wasps that readily find and attack it on cabbage plants. Could the lily leaf beetle enjoy a refuge from its biological control agents by feeding on nightshade? To date, the beetle has not been observed to lay its eggs on nightshade. However, the lily beetle does lay eggs, at least in the lab, on other plants that can support development of the larvae, such as Indian cucumber Medeola virginiana and claspleaf twisted stalk Streptopus amplexifolius. This summer, we plan to conduct experiments to see if the wasp Tetrastichus is confused when lily beetle larvae feed on these plants. More later... References: Ernst, C., Cappuccino, N., Arnason, J.T. 2007. Potential novel hosts for the lily leaf beetle Lilioceris lilii Scopoli (Coleoptera: Chrysomelidae) in eastern North America. Ecological Entomology 32:45–52 Morton, T.C., Vencl, F.V. 1998. Larval beetles form a defence from recycled host-plant chemicals discharged as fecal wastes. Journal of Chemical Ecology 24:765-785. Rossbach, A., Loehr, B., Vidal, S. 2006. Parasitism of Plutella xylostella L. feeding on a new host plant. Environmental Entomology 35:1350-1357. Schaffner, U., Müller, C. 2001. Exploitation of the fecal shield of the lily leaf beetle, Lilioceris lilii (Coleoptera: Chrysomelidae), by the specialist parasitoid Lemophagus pulcher(Hymenoptera: Ichneumonidae). Journal of Insect Behavior 14:739-757. Although only time will tell whether Tetrastichus setifer will control the lily leaf beetle as effectively in Ottawa as it does at the initial release sites in New England, biological control can boast some remarkable success stories here in Ontario. Arguably the most dramatic of these is the control of purple loosestrife by the beetle Galerucella calmariensis. G. calmariensis was one of two leaf beetles released throughout Canada in the 1990’s. It is now the dominant herbivore of purple loosestrife throughout Ontario, and its impact is visually striking. The photo below was taken along Greenbelt trail 10 near Shirley’s Bay in 2004, just west of Ottawa, where the beetle had caused substantial damage to the plants. Plants at that site produced only a few stunted flowering shoots. Compare the damaged plant above to a typical undamaged stand (below). The photo of the undamaged stand was taken at Petrie Islands to the east of Ottawa in 2004. A few beetles were spotted there that summer, but their population had not yet reached the level at which feeding damage was evident. While this would appear to be good evidence of the impact of the beetle on the plant, we don't actually know what the plants at the Shirley's Bay site looked like before the beetles did their damage. Perhaps the Shirley's Bay area was never a good site for loosestrife and the plants were stunted even before the beetle arrived. In fact, an article last fall in the Ottawa Citizen suggested that purple loosestrife is not well adapted to many wetland types and fails to thrive, and that this, more than the release of the beetle, explains the "fading away" of the "purple menace".
The best evidence for the impact of a biological control agent involves taking measurements of the target before and after the agent has been released. Unfortunately, funding for well designed before-and-after studies is often unavailable. An alternative approach involves comparing the target at sites with and without the agent, as long as those sites are matched for as many other factors as possible. To learn more about one such study, and to help track the distribution of the loosestrife beetle, visit purpleloosestrifebeetletracker.weebly.com. Today we submitted a petition to release a second biological control agent, the wasp Lemophagus errabundus, to control the lily leaf beetle. Like Tetrastichus setifer, profiled on the Biological Control page of this site, Lemophagus errabundus is a non-stinging parasitic wasp that is native to Europe. In Europe, L. errabundus attacks the beetle earlier in the season than T. setifer, so we hope it will prove to be an effective complement to our first agent. Biological control, which uses natural enemies to combat pest species, is generally considered to be an environmentally friendly way to control pests. However, many people are justifiably wary of introducing one exotic species to control another, given a few high-profile biological control disasters—think cane toads in Australia—dating from an earlier time when biological control was virtually unregulated. Since the 1900’s, however, biological control introductions in Canada have been regulated by the Canadian Food Inspection Agency (CFIA) and potential agents are now carefully scrutinized. Before we can import L. errabundus and release it, our petition will be read by a panel of experts, who will consider whether there is an unacceptable risk that the agent will attack non-target host species or have other unintended impacts. In an extensive array of tests in which L. errabundus was offered a variety of non-target species to attack, it parasitized only the lily leaf beetle and two closely related European lily beetles. Other, more-distant relatives of the lily beetle were not accepted as hosts by the wasp. Thus, the wasp appears to pose minimal risk to native North American beetles. Lemophagus errabundus has been released in the US and is successfully established in Massachusetts and Rhode Island, where it is contributing to lily beetle control along with Tetrastichus setifer. I’ll post an update when we have news on the status of our petition. Please return periodically for news about our project.
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AuthorNaomi Cappuccino was a member of the Department of Biology at Carleton University in Ottawa, Ontario, Canada. She is now retired and no longer updating this site. Archives
June 2021
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