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Impatient for the Parasitoids

In the summer of 2001, when my garden got hit by Asiatic lily leaf beetles (Lilioceris lilli), I searched the Web to identify them. It wasn’t hard: lots of gardeners were complaining about the devastation caused by these little red invaders. But I was glad to read that the Biological Control Lab of the University of Rhode Island, was studying the beetle’s natural enemies.

Dr. Richard Casagrande there told me they were hopeful about Tetrastichus setifer, a wasp less than three millimeters long, that doesn’t sting humans, and in Europe, is a major control of L. lilli. The female wasp lays her eggs in a plant leaf next to the beetle larvae. Ironically, the shield of feces the larva secretes, which probably repels birds, actually stimulates the wasp to oviposit. When the wasp larvae emerge, they eat the beetle larvae. The wasp is called a “parasitoid” — sort of midway between a parasite and a predator.

In the summer of 2002 I called again, hopeful of good news. They were trying to figure out why some of their T. setifer succeeded in wintering over, but not all of them. I realized it was going to take a while yet, before these wasps reached my garden.

This year I learned about the success of T. setifer at Elm Bank Horticulture Center in Wellesley. The wasp has controlled the beetle so well there, that URI had to provide the Massachusetts Horticultural Society with more beetles, to keep the wasps increasing!

No one knows how fast the wasps will spread. Casagrande says he looks forward to sometime holding a “giveaway day.” But they’re not announcing one yet.

URI also looked at three more European wasps for controlling L. lilli: similar to T. setifer, but emerging from winter dormancy — and hitting the beetle — earlier in the spring. One was rejected because it also attacked a native beetle, but the other two have been approved by the USDA and released by URI. Diaparsis jucunda, from higher elevations with cooler climates, should do well inland in New England; Lemophagus errabundus near the coast. Casagrande says he thinks these two are established in test plots, but can’t confirm it 'til larvae counts are available in June or July.

With plants, I’m used to working with the cycles of Nature: being patient, watching them grow in their own sweet time. But I want these insects now! “Biocontrol takes a while,” says Casagrande. “We’re movin’ along.”

© Copyright 2005 Catherine Holmes Clark

Published in the six Nashoba Publications papers on Friday, 29 April 2005

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