Saskatchewan’s newest horticultural pest.
It’s taken a while to get here, but it’s made it. The lily leaf beetle (Lilioceris lilii), native to Europe and Asia, was accidentally introduced into North America (specifically, Montreal) in the early 1940s, most likely through importations of flowering (potted) bulbs. Its spread in North America is also attributed to the sale and movement of potted lilies, which can carry eggs and larvae on the leaves, and pupae and not-yet-emerged adults in the soil.
Its Euroasian distribution — whereever lilies grow from the Mediterranean to Scandinavia and east to Siberia, and up to altitudes of 2,000 metres — indicates its tolerance to a wide climatic range, hence its ability to thrive in most of North America.
Since its introduction, the beetle has spread quickly and is now found in all Canadian provinces except British Columbia. It was first reported in Saskatchewan in 2015 from Saskatoon, Tisdale and Leask, but now has also been seen in Prince Albert and the Regina area.
Host plants
Both larval and adult beetles feed on all above-ground parts of true lilies (rendering its usual common name somewhat misleading), including fritillarias, as well as lilyof-the-valley, Solomon’s seal, potato, flowering tobacco, hollyhock and hosta. However, calla lilies, canna lilies and day lilies are immune to attack.
Life cycle
Despite some reports to the contrary, the beetle has but one generation per year. The bright red adults are 8 to 10 millimetres long and overwinter in soil, leaf litter or debris, emerging in the spring when they mate and feed on the first leaves of host plants. Eggs are soon laid, in groups of two to 16 on the underside of leaves, and egg laying continues as long as fresh foliage is available.
A female may lay more than 300 eggs. Eggs hatch after about a week, and there are four larval stages. As they develop, larvae coat themselves in a thick, black ‘fecal shield’ which serves both to camouflage them and to dissuade would-be predators.
The larval life lasts about three weeks; then the mature larva drops to the ground and builds a white cocoon in the soil in which to metamorphose (change to an adult). New generation adults emerge from the soil in late summer, feed briefly, and then find an overwintering site.
Control
For most gardeners, early and frequent inspection of potential host plants, followed by squishing of ‘the enemy’ is recommended (wear gloves, of course!). For those averse to this practice, and for gardeners/ horticulturists with large numbers of lilies, some form of chemical treatment may be necessary. If so, bear in mind that some synthetic insecticides (and some home-made recipes) are broad-spectrum (toxic to a range of insect pests) and persistent.
Choose a short-lasting product such as a synthetic pyrethroid that works on contact with the pest. Apply when the danger to other (beneficial) insects is minimal, for example, in the evening when most pollinators have left for the day.
Because the beetle is an introduced species, it has few natural enemies (predators and parasites) to regulate its numbers. However, three European parasitic wasps have been identified as suitable biological control agents, have been released, and are now established in New England.
The female wasp lays its eggs adjacent to beetle grubs. (Apparently, the wasp locates grubs by the smell of the fecal shield.) Newly hatched wasp larvae burrow into the grub, which is then slowly eaten from within. One of the wasps, Tetrastichus setifer, which appears well suited to our more rigorous Canadian winters, has been released and is now well-established in Quebec and Ontario. Its suitability is under test in Alberta (Olds, St. Albert and Calgary), but not yet in Saskatchewan.
Cedric Gillott is a retired entomologist in the Department of Biology, University of Saskatchewan.
This column is provided courtesy of the Saskatchewan Perennial Society (SPS; saskperennial@hotmail.com ). Check our website (www. saskperennial.ca) or Facebook page (www.facebook.com/saskperennial) for a list of upcoming gardening events: June 16, 9 a.m. or June 19, 6:30 p.m. – open to all. Volunteer at SPS Labour and Learn at the public Meditation and Rose Gardens, Forestry Farm Park and Zoo. Jun 24, 11 a.m. to 5 p.m. – Artists in Bloom, Honeywood Nursery, near Parkside, SK.