The Valley Elderberry Long Horned Beetle (Desmocerus californicus dimorphus)

An Endangered Pollinator in a Diminishing Ecosystem

By Vicki Wojcik, Pollinator Partnership

Bog Copper male.
Female valley elderberry longhorn beetle. Photo by Charles Webber © California Academy of Sciences.

Bog Copper female.
Male valley elderberry longhorn beetle. Photo by Jon Katz and Meghan Gilbart.

The American River Parkway in Sacramento is the final urban stop of the American River that flows from the Sierras near Lake Tahoe through the northern part of the California’s Central Valley. In California’s capitol, it meets the Sacramento River and then flows down through the Bay Delta into San Francisco Bay before it reaches the Pacific Ocean. The Valley Elderberry Longhorn Beetle, Desmocerus californicus dimorphus, calls this urban riparian forest in Sacramento home.

Elderberry beetles are intimately associated with their host plants (Sambucus spp.) for their entire lifecycle, displaying a mutualism in which a place to live is traded for help in reproduction. Females will lay their eggs on the bark of the elderberry; when the larvae hatch, they burrow into the stems. D. californicus dimorphus can stay in its larval stage for almost two years as it builds up energy and nutrient reserves. The larvae will pupate and emerge as adults between March and June. The spring and early summer are the best time to see these distinctive little beetles. The males range in length from about 1.25-2.5 cm with antennae that are as long as their bodies. Females are a little larger at about 1.9-2.5 cm in length with slightly shorter antennae. This is a common trait in insects as males often find females by scent; longer antennae provide them with an advantage. Color and pattern help you tell the males and females apart. The elytra (wing covers) of males are red-orange with four elongated dark spots; females are a darker metallic green with red margins on their elytra.

Like other beetle pollinators, they are destructive and messy, but their foraging activities dislodge and transfer pollen, helping to fertilize the elderberry seeds. Adults have been noted to eat leaf and floral tissues. Elderberry shrubs are the only hosts of Desmocerus californicus dimorphus, important for the riparian ecosystem, and a significant nectar source for other local pollinators. The Valley Elderberry Longhorn Beetle plays a key role in sustaining their populations.

Riverine systems and riparian zones that provided oases for native species once intersected California’s landscape. Development pressures have changed much of the landscape replacing the elderberry savannah with homes and farms. More than 90% of these riparian forests have been lots to development. In 1980 Desmocerus californicus dimorphus was listed a Threatened by the US Fish and Wildlife Service. Today, the Valley Elderberry Longhorn Beetle is only found in a few riparian parks that sit between patches of development.

The American River Parkway is a research site where the Pollinator Partnership collaborates with local authorities and land managers to improve the landscape for pollinators. We are studying how land managed in this urban park can be adjusted to improve the food resources that are present for pollinators including bees, wasps, butterflies, moths, hummingbirds, and the Valley Elderberry Longhorn Beetle. By removing invasive plant species and promoting natives we can maintain the fragments of this special ecosystem.

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