How to Manage Pests

UC Pest Management Guidelines

Dry Beans

Darkling Beetle

Scientific name: Blapstinus spp.

(Reviewed 8/07, updated 12/08)

In this Guideline:


Darkling beetle adults are from 0.13 to 0.25 inch (3.5 to 6 mm) long and vary from black or bluish black to rusty brown. They may be hidden by dust or a thin veneer of soil. Larvae are cylindrical, wirewormlike, soil-inhabiting worms that are light yellow to dark brown and range from 0.03 to 0.33 inch (0.8 to 8 mm) in length. They are often referred to as false wireworms.

Development from egg to adult may require 50 days during summer. Eggs hatch in 3 to 6 days and there can be five larval instars. The pupal period lasts 8 days or longer. Beetles are frequently numerous in spring and early summer and may be seen running on the ground but are more frequently found under clods or organic debris during daylight hours.


Damage is often caused during the seedling stage of plant growth. 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.


Start inspecting plants for darkling beetle damage along with other pests and their damage when the crop emerges. Treat if darkling beetles are causing a reduction in stand of the young plants. Infestations are frequently spotty, and damage and treatment may be confined to field margins or specific portions of the field.

Common name Amount/Acre** R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

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+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
1 Rotate chemicals with a different mode-of-action Group number, and do not use products with the same mode-of-action Group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a Group number of 1B; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode of action Group numbers are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Dry Beans
UC ANR Publication 3446

Insects and Mites

L. D. Godfrey, Entomology, UC Davis
R. F. Long, UC Cooperative Extension, Yolo County

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