Agriculture: Lettuce Pest Management Guidelines

Darkling Beetles

  • Darkling beetles: Blapstinus spp., Coelus spp.
  • Description of the Pest

    Darkling beetles (tenebrionids) are dull bluish black or brown, and about 0.25 inch long. The tips of their antennae are often enlarged, distinguishing them from predaceous ground beetles (carabids), which are beneficial.


    These beetles chew off seedlings or feed on foliage. Damage often begins on field edges because this pest typically invades from weeds or adjacent crops. Darkling ground beetles are most active at night.


    Cultural Control

    A shallow ditch filled with water can prevent movement of beetles from adjacent fields.

    Organically Acceptable Methods

    Use cultural controls in an organically certified crop.

    Monitoring and Treatment Decisions

    If chewed-off seedlings are found, and darkling ground beetles are present, apply an insecticide. A bait (Permethrin cutworm bait) placed around the edge of the field is usually sufficient.

    Common name Amount per acre** REI‡ PHI‡
    (Example trade name) (hours) (days)
    Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.
    (Mustang) 2.4–4.3 fl oz 12 1
    COMMENTS: Maximum rate 28.5 fl oz/acre per season
    (Permethrin cutworm bait) 40 lb 12 1
    (Ambush, Pounce 25WP) Label rates 12 1
    COMMENTS: Do not use if leafminers are present.
    (Asana XL) Label rates 12 7
    COMMENTS: For use on head lettuce only. Do not use if leafminers are present.
    ** Mix with enough water to provide complete coverage.
    Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) 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.
    * Permit required from county agricultural commissioner for purchase or use.
    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).
    Text Updated: 04/17
    Treatment Table Updated: 04/17