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Rare, Controversial Beetle Still Hangs On in Delta

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Valley elderberry longhorned beetle | Photo: Jon Katz and Joe Silveira, U.S. Fish and Wildlife Service
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An explanatory series focusing on one of the most complex issues facing California: water sharing. And at its core is the Sacramento-San Joaquin Bay Delta. Stay with kcet.org/baydelta for all the project's stories.

The Threatened Delta smelt is almost certainly the most controversial Delta wildlife species, but a tiny beetle might just give the smelt a run for its money when it comes to attracting the wrath of foes of endangered species protection.

The valley elderberry longhorned beetle, Desmocerus californicus dimorphus, an elegant-looking black and red critter usually between a half inch and an inch long, depends on the Central Valley's riparian forests for its living. In particular, the beetle needs old-growth elder thickets in order to reproduce. Such forests were once incredibly common in the Delta, as well as along the Central Valley streams that feed the Delta.

But 95 percent of the beetle's habitat has been destroyed since the Gold Rush, and since 1980 the valley elderberry longhorned beetle has been listed as Threatened under the U.S. Endangered Species Act. In 2010, developers and their allies tried to get the beetle delisted. But wildlife advocates argued back -- and the science backed them up.

There's a problem with gauging how well the beetle is doing under Endangered Species Act protection: It's long been really hard to know whether a particular stand of elders actually has the beetles in it.

Valley elderberry longhorned beetles lay their eggs on the stems of elderberry shrubs, usually Sambucus nigra, the blue elderberry. (There's some evidence that the beetles may use red and black elderberries, two native varieties of Sambucus racemosa, on rare occasions.) The larvae hatch out, tunnel into the shrubs' soft wood, and feed on the tissue inside the stems' newer growth. The larvae may remain inside the stem for 1-2 years, molting several times as they grow. After their third molt the larvae emerge from the stems, creating a so-called "exit hole," which they then re-enter to pupate, plugging the hole back up with chewed plant material.

When the adults emerge from the pupa inside the stem, they may remain there for several weeks, or they may come out into the open air almost immediately. Either way, they emerge by chewing their way back out of the exit hole when the elderberries bloom, then live for perhaps a month as adults as they mate, eat pollen and nectar, lay eggs, and die.

Since the beetle larvae need young stems that have enough fiber in them to keep them alive and growing for a year or two, that means choosing elderberry plants whose recent growth has stems an inch or more thick. And that means the shrub has to be old, a decade or more.

Elders don't get much respect in the Delta, or, for that matter, elsewhere in California. The berries of the blue elder are pleasant enough, and birds gorge on them. But unlike other native shrub species like manzanitas and ceanothus, elders don't have much of a public constituency. They're weedy looking and unkempt. They get big fast, and their wood is fragile.

And so they get cut down without the public raising much of a fuss. For 35 years, about the only thing saving the last of the valley elderberry longhorned beetle's habitat, in the Delta and elsewhere in the Valley, has been the Endangered Species Act.

Which is probably why, in 2010, the Pacific Legal Foundation -- a longtime ally of developers seeking to remove the Endangered Species Act as an obstacle to their businesses -- petitioned the U.S. Fish and Wildlife Service to delist the beetle, citing evidence that the beetle was more common than earlier suspected, and that much of the beetle's habitat was protected already.

That was just the latest salvo against the beetle's protection. The species had briefly become a conservative talking point during the mid-1990s, when the 104th Congress was pushing back hard on endangered species protection and other environmental regulations. Delta-area Representative Richard Pombo led that charge for some years, often armed with anecdotes about endangered species protection interfering with honest folks' livelihood that turned out not to bear much scrutiny. So it was with certain tall tales about the valley elderberry longhorned beetle, some of which are still heard today.

Chief among the threats the protected beetle was said to pose California's beleaguered human population was interference with levee repairs. Preserving those weedy elders on the off chance beetles might be living in them exposed thousands of Californians whose homes were built on flood plains to the specter of property loss, injury, or even drowning.

The idea of flooding being a threat may seem remote in our multi-year drought, but in the winter of 1996-1997, when heavy warm rains in December and January melted snowpack and prompted levee failures, the beetle came in for heavy criticism in talk radio and similar media. The eventual revelation that none of the levee failures stemmed from deferred maintenance on behalf of protecting the beetle didn't slow the talk down much. Nor did the fact that a non-zero amount of Richard Pombo's business activity prior to his election to Congress had consisted of developing housing in the Delta's floodplains.

But the floodwater receded, having damaged or destroyed thousands of homes, and the beetle mostly receded from public consideration a little time after. But the development trade and flood control agencies still had to spend time accounting for the beetle's Critical Habitat whenever one of their projects involved federal funding. That burden was what prompted the 2010 petition to delist the beetle.

And just as facts didn't support the 1990s' tall tales about the beetle causing floods, it turned out the science didn't back the Pacific Legal Foundation's claims. It's just really hard to be certain how many of the beetles exist in a particular area. Not only do the beetle adults only show themselves for a few weeks each year, but the beetle females are almost indistinguishable from female California elderberry longhorned beetles, a close cousin that's a lot more common.

As a result, biologists had been using exit holes in elder shrubs as a proxy metric for estimating valley elderberry longhorned beetle populations, but there were problems there as well. California elderberry longhorned beetles made the same kind of exit holes, which were often hard to find in the best of conditions, and could also be mistaken for holes made by other animals. Some adults emerge from the stems beneath the soil level, which means no readily visible holes. Some of the population census counts for the valley elderberry longhorned beetle included exit holes in dead stems. The data was kind of a mess.

In addition, the USFWS had for some time assumed that beetles were naturally going to be present in areas that had had their old-growth elder habitat restored.

But a bit of scientific research in the last couple years showed that things might be worse for the beetle than the petition to delist had claimed. Scientists used insect traps baited with pheromones produced by female valley elderberry longhorned beetles to attract males, known technically by the inadvertently charming term "headspace volatiles." They found that some places once thought to be strongholds of the valley elderberry longhorned beetle actually had none at all.

The southernmost part of what biologists had thought of as the valley elderberry longhorned beetle's range -- Kings, Kern and Tulare counties in the San Joaquin valley -- had only the California beetle cousins.

Instead of more abundant than expected, the beetles were actually far less abundant. And so in 2014, USFWS decided to keep the valley elderberry longhorned beetle on the Threatened list.

Despite staying on the Threatened list, the beetle is by no means out of the riparian woods. That pheromone trap study showed that some restored habitat, with plenty of appropriately aged elders, not far from areas known to be used by the beetles, had not been colonized by the beetles. It may be that the adults stay pretty close to their home shrubs when mating, rather than dispersing out into new areas to try to find new stands of elder.

As always with such relatively inconspicuous wildlife species, more study may end up telling us a lot. There's much we don't know about the beetle.

Which is, when you think about it, the best reason to protect the species in the first place. Letting it go extinct would be losing a potential source of wonder and fascination, like letting a library burn down before we can read the books inside.

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