The lily’s saviour could come in the form of a biocontrol agent. Naomi Cappuccino, an associate professor in the Department of Biology at Carleton University, has been conducting research into the biological control of the lily leaf beetle. Biological control uses natural enemies to combat pest species and reduce their populations. With the lily leaf beetle threatening to damage or destroy not only some of the most common lily cultivars but also heritage varieties and, in some areas, native species, the battle has taken on a new urgency. In a recent phone interview, Cappuccino said there have been reports of the lily leaf beetle on the Canada lily, a native of eastern North America as well as Michigan lily and Clapleaf Twistedstalk, a northern species that grows in the understory of the forest. It can be found growing in Gatineau Park near Ottawa, and is a rare species in certain areas of the U.S.. Cappuccino explained biocontrol sometimes works fabulously well and sometimes doesn’t. Fortunately, the introduction of a parasitic wasp, Tetrastichus setifer, by Cappuccino and her summer research students into test gardens in Ottawa, Montreal Botanic Garden, and native lily populations in Quebec is showing promising results. Cappuccino said the parasitism rate has been close to 90 per cent. This is exciting news for gardeners and, indeed, the entire lily industry. Cappuccino gives credit to the work done by Lisa Tewksbury, a research associate at the University of Rhode Island who together with Richard Casagrande, have been involved in a lily leaf beetle biocontrol project for many years. In a phone interview, Tewksbury said that in the U.S., before a classical biocontrol project can receive approval from the U.S.D.A., research must first show the insect planned for introduction is safe as well as host specific. While the work of her biocontrol lab began in 1996, releases did not take place until 2001. “The area where we started,” said Tewksbury, “is Wellesley, Massachusetts.” Her colleague, Casagrande, teaches a Master Gardener class in that area and many of the students have reported they no longer have a problem with the pests ravaging their lilies. Casagrande said the wasp or parasitoid has been successful in maintaining a very low population of lily leaf beetles. How does T. Setifer control the lily leaf beetle? First, although it is a wasp, it does not sting people and is tiny in size, almost like a gnat. The female wasp lays its eggs inside the larvae of the lily leaf beetle. According to Tewksbury it continues to look like a larvae and once it is done eating it drops to the ground and forms a soil cocoon around itself. Parasitic larvae take over the larvae of the lily leaf beetle. Normally, a lily leaf beetle would emerge, feed for awhile and then go back in and overwinter. Instead, the parasitoids remain in the cocoon and must overwinter. Tewksbury’s research involves three different types of parasitic wasps, all of which are currently in different parts of Switzerland. The wasps have been released in one or two test areas in each state in New England. Cappuccino is planning a controlled release of T. Setifer in Manitoba in 2016. Working together with the Manitoba Regional Lily Society, a test garden has been identified north of Winnipeg. This summer hundreds of lily beetles are being collected for the test site. Ed Czarnecki, President of the MRLS, and Ian Wise, an entomologist, will visit the garden about three times weekly. One of their tasks will be to count beetles and eggs. While there is no doubt that the lily leaf beetle is able to survive our harsh winter, it remains to be seen if the parasitoid wasp can overwinter. Tewksbury says that in some areas there are high numbers of the wasps but there is also a high mortality of the parasitoid each year. In order to assist in the spread and establishment of the wasp, Tewksbury recommends hand picking of adult lily beetles and egg masses and avoiding pesticide use. She also recommends not digging up bulbs which can disturb the site where a parasitoid is overwintering and minimizing mulching. Mulch might affect moisture levels not conducive to the wasp or that attract predators. In addition, Wise says a deep layer of mulch could hinder the wasp’s ability to emerge in spring. Both Tewksbury and Cappuccino say it will take about three to five years after releases of the parasitic wasp before we can expect to see a significant decrease in the lily beetle population. Tewksbury stresses the use of biological controls will not result in the eradication of the lily leaf beetle. In a biological control situation, parasitoids still need their host so gardeners will have to accept that the lily, just like most other plants in the garden, will still show occasional signs of pest damage. Providing T. Setifer chooses to establish itself in our lily gardens here in Manitoba, what should we do in the meantime? Nigel Strohman, owner of The Lily Nook, in Neepawa recommends using an all-purpose fertilizer (14-14-14) to aid healthy growth. He also suggests adding bone meal around the base of lilies and scratching it into the surface. There are many beautiful heritage lilies that have been bred in Manitoba and Saskatchewan, says Strohman. “To pull these up and destroy them is disheartening.” Is a regimen of picking and squishing beetles really effective? Following a successful pick and squish program every morning last summer at Assiniboine Park, Craig Gillespie, head gardener of the English Garden and Leo Mol Garden, says populations of the lily leaf beetle are down by almost 75 per cent. “We made a concerted effort to maintain good sanitation by cleaning up affected debris and removing and destroying all lily plant material that was cut down last fall,” said Gillespie. Last fall, an additional 500 lily bulbs were planted. Monitoring beetle populations remains necessary but only every two or three days. Samantha Tomchuk has been the groundskeeper at the University of Manitoba since 1983. A certified prairie horticulturist and arborist, Tomchuk grows numerous lilies in her St. Vital garden. As part of her daily monitoring routine, Tomchuk looks for any lily leaves missing their tips or those with a transparent or lacy appearance. Experience has told her those are most likely the leaves with eggs on the undersides. Sometimes it is too disgusting to remove the larvae so Tomchuk snips off the leaf with a pair of scissors and drops the leaf, together with the scissors, into a pail of soapy water.
Tetrastichus setifer, a parasitic wasp