Ecologist Calls For More Careful Use Of Biological Controls

In the August 22, 1997, issue of Science, Strong reviews a disturbing report published in the same issue from the University of Nebraska, Lincoln. The report reveals that a Eurasian weevil widely released in the United States and Canada has sometimes reduced its target population--non-native thistle plants that overrun livestock grazing areas--but also turned its appetite to five native thistle species.

Some of the native plants' seed production has been cut by 86 percent, dramatically impairing the plant's ability to reproduce. The weevil also appears to be pushing aside native picture-wing flies, which normally feed on the native thistles' flower heads.

And the weevil's distribution has expanded substantially, both naturally and through introductions that continue today. Since it was first released in 1968, the Eurasian weevil has been found in 24 states from California to New Jersey, and every Canadian province except Alberta.

Strong writes that the concurrent attacks should come as no surprise: They have occurred in similar biocontrol projects, and there was evidence before the weevil releases began that the Eurasian bugs would enjoy North American cuisine.

Carefully planned biological control, Strong writes, can provide great economic benefit, reduce the use of chemical pesticides, and even protect native species against non-native predators or competitors. However, he said in an interview, too few biocontrol projects are given requisite care.

"This is a huge policy issue for the United States," Strong said. "There's tremendous pressure from the agriculture industry--and the industries that supply agricultural biological controls--to find new agents, release them, and then go find more, without adequate study of their effects."

"It is important for us to start a broad public discussion about the conservation and environmental issues surrounding biological control."

In the Science article, Strong says it's essential to establish experimentally that the proposed control agent has an extremely limited "host range"--that its food preferences will keep it focused on its intended target, not native species.

"Biological control is an important arrow in the quiver of pest management, perhaps the only arrow in some cases of pests of grave concern," Strong writes in conclusion. "However, willy-nilly biological control without regard for environmental costs" can clearly have serious consequences.

Reference: Strong DR. 1997. Science 277:1058-1059.