Wasp could help battle red lily leaf beetle, but not soon

red lily leaf beetles mating
The red lily leaf beetle is spreading in Western New York, causing damage to lilies and fritillaria. This photo was taken in Buffalo. Photo courtesy Gordon Ballard

by Connie Oswald Stofko

A parasitic wasp could help Western New York gardeners battle the red lily leaf beetle, but that help is still years away, said John Farfaglia, extension educator with Cornell Cooperative Extension in Niagara County.

What to do now with red lily leaf beetle

Now is the time to look for the red lily leaf beetle, which can cause extensive damage to lilies and a spring bulb plant called fritillaria. The pests aren’t a problem for daylilies, which aren’t true lilies and grow from a tuber.

More and more Western New York gardeners are spotting this pest. Here’s an introduction to the problem and more information on what to do at this time of year. See details in this factsheet from Cornell University.

So far, the options for dealing with the red lily leaf beetle have been limited.

You can try picking the adults off, but that’s difficult because they’re fast.

The larvae are also difficult to handpick, and they’re disgusting. The larvae cover themselves in their own feces to fend off predators. Yuk! See the life cycles of the red lily leaf beetle here.

If handpicking doesn’t work, you could try a pesticide called neem oil, Farfaglia said, and if you’re going to take this path, now is the time to do it. He recommends neem oil for use by home gardeners because it is less toxic than other pesticides listed on the Cornell factsheet, and people have had reasonably good luck with it.

In addition, some of the other suggested pesticides are systemic and neem oil isn’t. If you use neem oil on the leaves, it won’t be carried to the flower, which would contaminate the nectar and pollen. That could kill bees and other pollinators and beneficial insects. Don’t use any insecticides, even neem oil, on plants with open flowers or you could endanger beneficial insects.

If you don’t want to handpick the pests or use insecticide, your final choice is to plant something other than lilies and fritillaria.

But there may be another defense on the horizon.

Helpful wasps may be coming our way– someday

Researchers at the University of Rhode Island identified three parasitic wasps that are natural enemies of the red lily leaf beetle, which is native to Europe. The wasps underwent thorough testing to be sure that they would not attack any native beetles here, then they were introduced to North America. (These tiny wasps don’t sting humans.)

A wasp lays its eggs inside the body of the lily leaf beetle larva. Upon hatching, the wasp larvae devour the beetle from the inside out.

The researchers released wasps in Massachusetts, Rhode Island, Maine and New Hampshire and later (2010) in Ottawa, Ontario.

The good news is that the number of red lily leaf beetles decreased where the parasitic wasps were released.

So can we release some parasitic wasps here? Unfortunately, no. You would need scientific funding to do that, Farfaglia said.

But the other piece of good news that has come out of the Rhode Island research is that the range of the wasps is increasing.

“I hope that the wasps spread here,” Farfaglia said. “Sometimes it takes years, sometimes it takes decades, but if there is a population they feed on, they will increase in that area.”

You can also help the researchers track these pests. If you have red lily leaf beetles and are in an area not already on their map, you can report it.

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3 Comments on “Wasp could help battle red lily leaf beetle, but not soon

  1. As the wasps are spreading, what DO they feed on, if they aren’t finding the red lily beetle? What is going to be controlling the wasp population?

  2. The wasps feed on red lily leaf beetles. If the wasps don’t find a new supply of that food, they will stay where they are. The red leaf lily beetles originated in Europe and were found in Massachusetts in 1992. They spread throughout New England and into New York State. We saw them in Western New York starting around 2014. The wasps were released in New England and in Ontario. We hope that the wasps will follow their food supply of red lily leaf beetles and eventually spread into Western New York. If you look at the distribution map of the red lily leaf beetle, there seems to be a pretty good supply of beetles from New England to WNY. (There seems to be a bit of a gap in central New York, but I don’t whether that means that the beetle isn’t there or that no one has reported it.) There seems to be a more continuous supply of red leaf lily beetles from Ontario to WNY. It may take awhile, but we hope the wasps will find their way here.

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