Invader invited to defend Delta
Matt Weiser
Sacramento Bee
08/06/2011
Lean out of a boat in the Sacramento-San Joaquin Delta, grab a handful of plants or a net full of fish, and you'll haul in a bunch of stuff that doesn't belong there.
The Delta is considered North America's most invaded estuary. About 200 foreign species have taken root here. A new one settles in about every nine months, usually when a cargo ship discharges ballast water or a homeowner dumps his aquarium in a ditch.
Ranging from Chinese clams and Atlantic fish to South American water weeds, they have crowded out native species in many areas. By some estimates, 95 percent of the Delta's biomass, or the totality of its organisms, are not native.
So it is hardly surprising that some Delta residents reacted with alarm last week when the California Department of Food and Agriculture announced it had intentionally added another invader to the mix: Megamelus scutellaris, a South American plant hopper.
The department released about 5,000 hoppers at three locations late in July. It hopes the new bug will take down another invader: water hyacinth, a floating weed that is a longtime irritant to boaters and water users.
"If it works, it would be great," said Candy Korth, owner of Korth's Pirate's Lair Marina near Isleton. "I just keep thinking, 'Oh my God, I hope there isn't unintended consequences from this bug.' How many times in the history of the world has something been introduced and then they realize: 'uh-oh.' "
Indeed, there are many such examples in the Delta. One is the striped bass, introduced in the late 1800s to create a commercial fishery. It remains an important sportfish, but has also become a voracious predator of native fish, including the threatened Delta smelt.
The arrival of the Megamelus hopper in the Delta came with little public notice. State agriculture department officials announced it only after the bugs had been released.
"It did seem to come as a surprise to everybody," said Bruce Herbold, a biologist at the U.S. Environmental Protection Agency and its foremost expert on the Delta's aquatic wildlife. "I would like to have known about it before they went off and released them."
The hopper, only slightly larger than a flea at adulthood, arrived by a very different route than most invasive species.
The U.S. Department of Agriculture spent several years conducting an environmental assessment to learn if the hopper might harm plants other than the target hyacinth.
In testing on dozens of other plants – first in its native South America, then in the U.S. – the department found the hopper would breed and feed on only a handful of other species, and it was unable to grow to adulthood on any of them.
The hopper works on hyacinth by inserting its needle-like mouth parts into the plant and feeding on its sap. This damages plant tissues, causing it to die.
