I toured a couple of very interesting farming operations in Klamath Falls this week. Both used natural geothermal hot water. One of them produced spider mites, the other tropical fish. Both have connections to invasive species.
Farming spider mites seems like a bad joke, but someone has to produce the eggs that serve as a food source for production of predator mites. This farm produces zillions of spider mites on lima beans in a series of large greenhouses, all kept at a toasty 90 degrees Farenheit by the abundant hot water. Each week, they fill the equivalent of 17 Dixie cups full of nearly microscopic spider mite eggs. Predator mites feast and grow on the eggs at a separate location.
Eventually, strawberry growers and other farmers and gardeners buy these biological control agents and use them instead of chemicals to keep spider mites below economic thresholds. That is good thing.
These same commercially-available predator mites negated an attempt at biological control of gorse (an invasive weed) on the south coast of Oregon a few years back. The Oregon Department of Agriculture (ODA) imported a gorse spider mite to eat the gorse. The biological control agent established readily and seemed to be stressing the plants, but the mite population soon crashed when a non-native predator mite showed up. The predator mite was the same species sold commercially as a biological control agent. It was a case of one biological control agent eating another!
The second farm produced cichlids for the tropical fish trade and tilapia for grocery stores. Both are raised in 85 degree Farenheit water in open ponds. This farm got its start several years back when a vector control official approached them about raising mosquito fish (Gambusia) in the warm water. Mosquito fish look like guppies, and, like a lot of fish, they eat mosquito larvae. Unfortunately, under favorable conditions, they can become invasive and displace native fish. Australia has serious Gambusia problems.
In Oregon, mosquito fish are allowed only in artificial water bodies not connected to natural systems. That is a reasonable policy considering the risks and benefits. More information on mosquito fish in Oregon is available at: http://www.dfw.state.or.us/fish/diseases/docs/backgrounder_WNV_gambusia.pdf