This week I attended an awards ceremony celebrating the success of a biological control project. Cereal leaf beetle (CLB), an invasive grain pest, arrived here a decade ago. Pesticide use in grain fields increased steadily. A team of scientists and regulators from Oregon and Washington banded together to bring in parasitic wasps that feed on CLB.
One parasite attacked CLB larvae, the other its eggs. The larval parasite established, and CLB parasitism rates now are up to 100% in some fields. Pesticide use against CLB has dropped dramatically. CLB will always be here, but hopefully at levels below economic thresholds.
That is the good news. There is some bad news. CLB continues to spread. It was reported for the first time in Jackson County this spring. The CLB biological control team has already released parasites there. Hopefully, they will establish there, too, and suppress CLB populations.
This is an example of biological control done well. The parasites are specific to the non-native invasive species target, and once established, they reduce the use of pesticides.
Biological control does not always work so well; there are plenty of examples of biological control done badly. Sometimes the introduced biological control agent itself has become a harmful invasive species. Many of the biological control-gone-bad examples around the world were introductions of generalist parasites or predators that were released by amateurs, though the US Department of Agriculture (USDA) has made a few mistakes, too.
Two examples from Oregon spring to mind: The multi-colored Asian lady beetle, a USDA-release, has become a pest because it overwinters in large numbers in houses. There is concern that it may be displacing native lady beetles.
Rynocyllus conicus, a weevil introduced as a biological control for invasive thistles also feeds on native thistles. Both of these were introduced decades ago when biological control wasn’t well regulated. Now official releases only happen after years of host-specificity testing. We’ve gotten better at biological control.
Islands are especially vulnerable to invasive species and provide numerous examples of the dark side of biological control. Here are some examples from Bermuda where I worked before coming to Oregon.
1.) Lizards were introduced to control fruit flies. The lizards preferred other prey and soon there were lizards everywhere. Kiskadees (a jay-like bird) were introduced to eat lizards, but they were noisy and preferred baby bluebirds. Then the fruit flies and the bluebirds disappeared, but the lizards and kiskadees persist to this day!
2.) Cane toads were introduced to control cockroaches. That didn’t work, but they eat honeybees by the hundreds and love monarch butterflies! These enormous toads become thin, dinner plate-sized road ornaments when they encounter cars. There is an old Bermuda joke that goes like this: “Why did the toad cross the road? To see his flat mate.”
Congratulations to USDA, Oregon Department of Agriculture, Washington State University, and Oregon State University for their award. Your work proves that non-native biological control agents have a place in the battle against invasive species.