Diaprepes root weevil—Diaprepes abbreviatus
This snout beetle (Curculionidae), also called citrus root weevil or diaprepes, feeds on citrus and more than 270 species of plants in 59 plant families. This beetle was inadvertently introduced from the Caribbean and occurs in at least coastal areas of Los Angeles, Orange, and San Diego Counties.
Identification
Adults are hard bodied and about 3/8 to 3/4 inch long with a long, tapered head and mouthparts. Coloration varies greatly and ranges from black to gray, orange, or yellow. Adults are commonly a mix of colors including blackish streaks. Adults can live 4 to 5 months, during which time a female can lay more than 1,000 eggs.
Eggs are oval, whitish, and about 1/25 inch long. They occur in groups of two to several dozen laid in a single layer in a gelatinous mass between leaves glued together.
Larvae are legless grubs with a brown head. They grow up to 1 inch long while developing through 10 or 11 increasingly larger instars over a period of 4 to 15 months. Pupae occur in a soil cell.
Monitor to confirm weevil presence.
- Dig and scrape away soil at the base of plants suspected of infestation and look for chewed roots and root crowns and the soil-dwelling weevil larvae and pupae.
- Examine hosts for chewed and notched leaves, frass (weevil excrement), and leaves glued together. Open glued leaves to observe whether diaprepes eggs are present.
- Place out special diaprepes traps. These consist of a base of black vanes that rest on the ground and as with a tree trunk induce adults to walk up and be caught in an inverted cup.
- Place tentlike metal screens under canopies and inspect inside these regularly for captured adults that emerged from soil.
Life cycle
Diaprepes root weevil develops through four life stages: egg, larva, pupa, and adult. After hatching the larvae drop to the soil and move briefly on the surface before boring in to chew and feed on roots and root crowns. After feeding for several months, larvae mature and pupate in soil. Adults will not emerge from compacted, dry soil; adult emergence commonly occurs after irrigation or rainfall.
Damage
Larvae chew roots and the root crown, causing severe decline or death of infested hosts. The nocturnal adults chew mostly young, tender leaves from the edges, causing irregular or semicircular notches and leaving dark frass (droppings) on foliage.
Solutions
If you find a weevil resembling Diaprepes abbreviatus in an area where it is not known to occur, place adults in a jar filled with rubbing alcohol and take them to the local county agricultural commissioner or University of California (UC) Cooperative Extension office for positive identification.
Parasitic (entomopathogenic) nematodes (e.g., Heterorhabditis or Steinernema spp.) can be drenched onto soil beneath infested plants to reduce larval abundance if soil is well drained (e.g., high in organic matter or sandy) and not compacted or high in clay content. Soil must be warm (at least 60°F) and moist (well irrigated) but not soggy before applying nematodes and for 2 weeks after application. If warranted, irrigate every 2 to 3 days after applying nematodes to soil. During hot weather, apply nematodes in the early morning or evening.
Applying a systemic insecticide (e.g., imidacloprid) to soil or trunks may control both adults and larvae. Foliar sprays are generally not recommended because of limited efficacy and adults move between numerous plant species. If plants are especially susceptible to foliage damage, a persistent, broad-spectrum insecticide can be sprayed on leaves, such as carbaryl* mixed with horticultural oil.
For more information and photographs, see Diaprepes Root Weevil (PDF) from the University of California and Diaprepes abbreviatus (Diaprepes Root Weevil) from the California Department of Food and Agriculture.
Adapted from Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Statewide Integrated Pest Management Program (UC IPM).
*As of August 1, 2020, pesticides containing the active ingredient carbaryl are restricted use materials in California. A valid pesticide applicator’s license is required for their possession and use. For more information see the California Department of Pesticide Regulation website. |
