Agave and yucca weevils—Scyphophorus species
Agave weevil, Scyphophorus acupunctatus, and yucca weevil, S. yuccae, can occur throughout California where host plants grow. These weevils are pests primarily in southern California. They resemble each other, and except for differing hosts have much the same biology and management.
Identification
Adults are most commonly observed on hosts from late winter through summer. They are up to 3/4 inch long and have long, narrow, snoutlike mouthparts and a small, elongated head. Adults are black with a smooth, finely punctured thorax and lengthwise grooves on the wing covers.
Mature larvae are up to 1 inch long. They are cylindrical, legless, and white or yellowish with a brown head. Larvae feed hidden in the apical meristem (central growing point) of hosts, the base of green flower stalks, and in roots.
Life cycle
Weevils develop through four life stages: egg, larva, pupa, and adult. After mating, adult females chew an egg-laying tunnel in the base of hosts. After hatching from an egg, larvae develop through several increasingly larger instars as they feed and tunnel in plants. Mature larvae generally exit hosts to pupate in topsoil; pupae can also occur in the base of plants.
One generation egg to adult can be completed in less than 2 months when temperatures are warm. There can be 4 or 5 generations per year.
Damage
Adults feed on host sap and this does not threaten plant health. Adult feeding causes discolored, punctured spots or small holes in the foliage.
Larvae bore in the base of hosts, causing plants to decline and facilitating entry of plant pathogens. Larval feeding in combination with decay microorganisms that colonize wounded tissue commonly cause infested plants to collapse and die.
Agave weevil larvae infest various Agave spp. They bore in the plant base and upper roots of large species of agave that have wide leaf blades and bluish or gray leaf coloring, such as century plant (A. americana). The more narrow-leaved, smaller agaves are less commonly infested. Yucca weevil larvae infest chaparral yucca, or Our Lord’s candle, Hesperoyucca (=Yucca) whipplei.
Solutions
Direct control of agave and yucca weevils is difficult; even with regular inspection of hosts, the insects are often not observed until the plant starts to collapse. Preventive measures are the only effective controls.
Provide plants with good growing conditions and proper cultural care. Agave and yucca require well drained soils, full sun, and little or no irrigation after they become established. Plant on a mound or raised bed to improve soil drainage. Where feasible, before planting amend soil with sand or other porous materials to improve drainage. Minimize irrigation of established hosts. After any irrigation, allow topsoil to dry between watering events.
To help protect nearby hosts, remove dying hosts and the immediately adjacent soil where larvae may be pupating. Promptly dispose of infested material in ways that prevent weevils from emerging or escaping. Where agave weevil has been a problem, consider planting the smaller, narrower-leaved agave species. If applied BEFORE plants become infested, certain systemic insecticides (e.g., imidacloprid) may provide control.
For more information see Agave Snout Weevil - Desert Gardening Guides (PDF) and Review of Scyphophorus (Curculionidae: Rhynchophorinae).
Adapted from Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Statewide Integrated Pest Management Program (UC IPM). |
Larvae of agave weevil.
Egg-laying tunnel entrance chewed by adult agave weevil.
Adult yucca weevil.
Adult yucca weevil, top view.
The front legs, head, and mouthparts of agave weevil.
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