Whitehall Project: Leafy Spurge Flea Beetles, where do they work?

There are 6 species of flea beetles approved for release on leafy spurge. They are: Aphthona abdominalis

Aphthona cyparissiae

Aphthona czwalinae

Aphthona flava

Aphthona lacertosa

Aphthona nigrascutis

They are a very small beetle with a back "hopping" leg somewhat like a grasshopper. Some of these species are black, and some are coppery brown. The adults emerge from the soil from mid-June to mid-July in Montana. Adult feeding creates many holes and chewed edges on spurge leaves. They make an attractant pheromone (a chemical scent signal) that caused them to stay together in an area. The adults scatter their minute eggs on the ground around spurge plants. If not eaten by ants and other predators, the minute larvae soon hatch and burrow into the soil. The larvae do the most damage to spurge (which has a deep and extensive root system) by feeding on the root hairs (hair like extensions of the root tips which take up most of the water and nutrients a plant needs) which often kills the plant over time. In the fall the larvae pupate near the surface of the soil and overwinter as pupae. Then in June and July, the adults emerge and do it all again.

In Montana these flea beetles can build up to huge numbers and almost completely wipe out leafy spurge on dry warm sites. Remember however, no biological control agent is likely to completely wipe out its host plant. If that had happened in Eurasia where the insects and weed species co-evolved, they would have gone extinct. When we reach a point with an established noxious weed that we choose to use biological control we are saying that we have given up trying to completely eradicate that weed and are hoping to bring it back under control (i.e., just another pretty flower here and there) using the insects that evolved with it and keep it under control on its home continent. Our noxious weeds are not weeds on their continents of origin and, some of our native North American "pretty flowers" have become noxious weeds on other continents.

The unfortunate limitation of the leafy spurge flea beetles is that the larvae drown if the soil is saturated for more than a day or so, allowing leafy spurge to survive on that site. So, here are examples of sites where the flea beetles do not seem to work in our area: 1) along ditches, streams and irrigation canals, 2) in swampy areas or any area that floods periodically, 3) around large ant piles, 4) in areas that are cool and shady like thick river bottoms or evergreen forested sites, 5) at high elevations such as along the Continental divide, and 6) where flood-irrigation or heavy irrigation is used. I have seen sewage drain fields be an "oasis" of tall healthy spurge in an area where almost all the rest of the spurge was killed by the flea beetles. Unfortunately, spurge can survive on all these site types...

In these types of areas, try using sheep/goats or spraying one of the herbicides that are approved for wet areas (follow the label!). Pulling and mowing do not usually kill leafy spurge because of its extensive/deep roots. The County Weed District does have a cost-share herbicide program: Jill Allen 406-225-4165. For insects call the Whitehall Project: Alycia 406-565-3995 or Todd 406-498-5236.

We are still collecting leafy spurge flea beetles for a short time. We should have the knapweed root boring weevil in late July/August. We also have stem galling insects for Russian knapweed and may have the Canada thistle rust fungus in Sept. so, feel free to call and reserve a release. Releases are free though voluntary donations are always welcome. There are also private companies that sell these and other biological weed control agents. Keep at those weeds!!