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Maruca pod borer (Maruca vitrata)

Maruca vitrata, the legume or spotted pod borer (Lepidoptera: Crambidae), is one of the most damaging pests of tropical pulse legumes including cowpea, pigeonpea, mungbean, urdbean and lablab. The pest causes an estimated USD 30 million in annual losses to Indian legume agriculture and is the primary biotic constraint on commercial monsoon-season chikkudu cultivation (Lablab Chikkudu).

Identification and symptoms

Adults are small (about 1 cm) moths with brown forewings carrying a characteristic transverse pale band and white hindwings with dark margins. Larvae are pale-green with rows of dark spots and a darker head capsule. Damage first appears as webbed-together leaves, buds and flowers; older larvae bore into pods and feed on the developing seeds from within.

Host crops and life cycle

The pest is highly polyphagous on Fabaceae. In India it cycles between cowpea, pigeonpea, mungbean, urdbean, lablab (Lablab Chikkudu) and cluster bean (Cluster Beans). Females lay eggs near floral buds; larvae develop through 5 instars in 8-14 days before pupating in webbed leaf or pod material.

Damage and economic impact

Because larvae feed concealed inside webbed flowers and pods, they are physically protected from both natural enemies and contact insecticides. Pod damage of 50-80% is routine in unprotected legume crops during peak infestation, and the pest is the largest single biotic loss factor in tropical pulses. The estimated annual loss in India is approximately USD 30 million.

Management

ICAR/ICRISAT-recommended IPM modules use sequential sprays of chlorantraniliprole 18.5 SC at 0.5 mL/L followed by azadirachtin 0.15% at 4 mL/L and emamectin benzoate 5 SG at 0.5 g/L, beginning at 50% flowering at 10-day intervals. Field sanitation, pheromone trap monitoring and conserving natural enemies including Trichogramma spp. parasitoids are supporting practices. Rotation of mode-of-action insecticides is critical to manage resistance.

See also: Lablab Chikkudu, Cluster Beans.

References

  1. The Legume Pod Borer, Maruca vitrata: Bionomics and Management. ICRISAT Information Bulletin.
  2. Development of pest management modules for Maruca vitrata in cowpea. Indian Journal of Agricultural Sciences, ICAR.