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iNaturalist observation of the month: Yucca weevil

By Patricia Simpson | iNaturalist

Up until May 9, no observations of yucca weevils (Scyphophorus yuccae) had been made at Mission Trails Regional Park on iNaturalist.org. That day, these rather large (about 5/8-inch) black snout beetles caught the attention of several hikers who came across a severed chaparral yucca (Hesperoyucca whipplei) stem along the trail. Adult beetles had congregated in numbers on top of the sectioned plant to create quite a tableau as shown in an observation by user egu5037, found online at bit.ly/2C2hQ1v.

The yucca weevil, as its name indicates, spends its life cycle on plants of the genera yucca and hesperoyucca. It is active roughly from April to July but often goes unnoticed. The adults spend time on the lower portion of the plant. The larvae bore into the flower stalk and tunnel their way up to the inflorescence where they pupate and emerge in the fall. Though this activity damages the plant and might reduce seed production, it doesn’t affect the health of the chaparral yucca too much since the plant dies down anyway after flowering. But for other species of yucca, an infestation of weevils can mean premature death. You can learn about managing the pest at home at bit.ly/2oouU7K.

Yucca weevils (iNaturalist)

Side note: For the chaparral yucca plant, which flowers only once before it dies, removing a flowering stalk can have a significant negative impact on propagation of future plants in that area.

—Patricia Simpson is a trail guide at Mission Trails Regional Park.

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