More bug species are not necessarily better for biological control of invasive weeds, says a study by University of British Columbia UBC biodiversity experts.
A UBC release says that most biocontrol programs combine many different enemies — typically about three different species, but sometimes as many as 25 — with the hope that at least one will prove effective.
However, some combinations of enemy species can actually end up competing or interfering with each other, instead of attacking the weed.
“It’s important to get the right combination of biocontrol agents, as testing species is costly and time consuming, and no amount of testing can eliminate the risk that something unexpected will occur with the introduction of a new species,” Andrea Stephens, lead author on the paper published in the Proceedings of the Royal Society B, said in the release.
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The researchers did a meta-analysis — a review of several studies on the subject. Of the 75 combinations investigated, about a quarter appeared to have a smaller combined impact than expected. The researchers suggest simple species combination rules could improve the effectiveness of biocontrol programs.
One of the studies researchers analyzed focused on three agents (two species of weevils and a fly) that have been released in western North America to control two species of invasive plants, diffuse and spotted knapweed. The weevils consume the fly larvae, nullifying the effectiveness of the fly.
