How to Manage Pests
UC Pest Management Guidelines
Scientific Names: Blapstinus spp., Coelus spp., and others
(Reviewed 12/09, updated 6/12, pesticides updated 5/16, corrected 8/16)
In this Guideline:
Description of the Pests
Darkling beetle adults are from 0.13 to 0.25 inch long (3 to 6 mm) and vary from black or bluish black to rusty brown. Do not confuse beetles (Tenebrionidae) with predatory ground beetles (Carabidae), which prey on various soil dwelling pests. Darkling beetles generally have clubbed antennae whereas carabids do not. Darkling beetles may be hidden by dust or a thin layer of soil. Larvae are cylindrical, wireworm-like, soil-inhabiting worms that are light yellow to dark brown and range from 0.03 to 0.33 inch (1–8 mm) in length. They are often referred to as false wireworms.
Darkling beetles are generally not a problem unless large populations build up when the plants are in the seedling stage. Young plants may be girdled or cut off at or below the soil surface. After the plants reach a height of 5 to 6 inches, darkling beetles are usually not a problem. However, further feeding may occur on flower blossoms during bloom, on the undersides of leaves, and on the netting of mature melons. They can also bore into fruit where it rests on the ground.
There are cultural control methods that can reduce darkling beetle damage.
Start monitoring for darkling beetles at fruiting. Treat whenever beetles are observed feeding on plants, flowers, or fruit. Also treat when beetles are observed moving into cucurbits or melons from fallow or alfalfa hay fields.
UC IPM Pest Management Guidelines:
Insects and Mites
E. T. Natwick, UC Cooperative Extension, Imperial County
Acknowledgment for contributions to Insects and Mites:R. L. Coviello, UC Cooperative Extension, Fresno County
C. B. Fouche, UC Cooperative Extension, San Joaquin County
L. D. Godfrey, Entomology, UC Davis
J. B. LeBoeuf, AgiData Sensing, Inc., Fresno
M. Murray, UC Cooperative Extension, Colusa and Glenn counties
C. G. Summers, Entomology, UC Davis and Kearney Agricultural Center, Parlier