Southwestern Corn Borer

Injury and Pest Symptoms

Southwestern corn borer larva tunneling in corn stalk.

Whorl-stage corn

  • First- and second-stage larvae feed 9 to10 days in whorl, creating pinholes and small, circular lesions or "windows" to large elongated holes
  • Third-stage larvae depart the whorl, crawl down the plant, and burrow into the stalk
  • Tunneling may damage the growing point, causing "dead heart" and stunted plants
  • Large larvae tunnel vertically in the stalk
  • Tunneling reduces uptake of nutrients and water, which stunts plant height and reduces grain yield

Reproductive-stage corn

  • Early-stage larvae feed between husk leaves, on ear shoots and behind leaf sheaths
  • Late-stage larvae may feed on kernels, often near base of ear, but eventually tunnel into stalk (photos below) and tunnel may be 12 inches long
Kernel damage caused by southwestern corn borer (left) and corn stalk with corn borer entrance hole at plant base (right).

Kernel damage and entrance hole at plant base

Corn stalk girdled by southwestern corn borer larva.

Pest Status and Importance

  • In corn, 29% yield loss reported from stalk tunneling
  • Additional harvest losses of 50 to 75% can occur during fall when larvae girdle stalks, causing corn to lodge
  • Kernel feeding can increase aflatoxin levels in grain
  • In sorghum, up to 50% yield loss may occur

Facts on Southwestern Corn Borer

  • Common name: southwestern corn borer
  • Latin name: Diatraea grandiosella, family Crambidae
  • Description
    • Adult: dull-white or buff-colored moth; wingspan 3/4 to 1 1/2 inches (19 to 38 mm)
    • Larva: (summer phase) creamy white with large, raised brown or black tubercles on each body segment; (winter phase) creamy white and without distinctive spots; head black (instars 1 to 3) or reddish brown (instars 4 to 6)
    • Egg: flat and oval, laid in clusters; pale yellow-green when first laid, but within 36 hours develops three orange-red lines (see below)
Southwestern corn borer larvae - winter phase and summer phase.

Larvae of southwestern corn borer: winter (diapause) phase (top)
and summer phase (bottom)

Southwestern corn borer adult and eggs.

Origin and Distribution

  • Native to North America, including Mexico
  • Occurs in southern corn regions from Arizona to western Georgia and northward to south-central Kansas, southern Illinois and southern Missouri
  • Larvae cannot survive in regions where the 10-year average January temperature is below 19 F

Similar Species and Life History

Similar Species

  • European corn borer and sugarcane borer

Life History

  • Larvae pupate in the spring inside cornstalks at the base of plants
  • Females lay up to 400 eggs on leaves, stalks, and ear husks
  • Eggs hatch in 4 to 7 days
  • Early-stage larvae feed in corn whorls, behind leaf sheaths, or on husk leaves, ear shoots, and kernels
  • Late-stage larvae tunnel into the stalk
  • Larvae complete 5 to 6 stages; summer generation requires 38 to 56 days
  • Overwintering (diapause) larvae crawl to base of stalk, tunnel inside, and create an internal girdle
  • Larvae are cannibalistic; usually only one larva overwinters in base of stalk
  • 2 to 3 generations occur each year depending on elevation and latitude
  • Fungus, Beauveria bassiana, may kill 50% of larvae

Integrated Pest Management Practices

Bt Corn Hybrids

  • Pioneer® brand products containing a corn borer trait provide excellent control; contact a Pioneer representative for trait availability

Non-Bt Corn Hybrids

  • Plant early: More mature plants are damaged less by 2nd and 3rd generation larvae Pioneer® brand products containing a corn borer trait provide excellent control; contact a Pioneer representative for trait availability
  • Scout fields: Economic threshold is 20 to 25% of plants infested with eggs or young larvae; pheromone traps can predict moth flight and time to scout; contact state extension entomologist for resource information and scouting procedures
  • Insecticides: Application of insecticide must occur before larvae tunnel into stalk; contact your state extension entomologist for recommended insecticides
  • Postharvest crop destruction: Stalk shredding and minimum tillage that breaks the stalk at ground level reduces overwintering survival

Photos and Text

Marlin E. Rice (Pioneer); Reviewed by Scott Stewart (University of Tennessee), and Paula Davis and Herb Eichenseer (Pioneer)