The semilooper feeds on leaflets and pods. Young larvae scrape the leaflets, while the grown-ups nibble on buds, flowers, pods, leaving the basal part of the pod with peduncle. While feeding on the pods, the looper leaves ragged and irregular damage of the pod wall. Leaves appear perforated and during a heavy infestation, leaves can be skeletonized. In severe cases, plants may become completely defoliated. Usually, symptoms are confused with bird damage.
The damage is caused by the larvae of Autographa nigrisigna. The moth of the semilooper has patterned fore wings. The eggs are spherical and are laid in clumps of 40 eggs on the leaflets. The larvae and semilooper are green in colour. One generation takes about 4 weeks to develop. Egg period takes about 3-6 days and the larval period is completed in 8-30 days, while the pupal period occupies 5-10 days.
Promote predator species like spiders, lacewings, ants and other natural enemies by avoiding the use of pesticides. Release Trichogramma chilonis at weekly intervals @ 1.5 lakh/ha for four weeks. Bio-insecticides based on NPV (Nucleopolyhedrovirus), Bacillus thuringiensis or Beauveria bassiana can also help to control semiloopers. Botanical products, such as neem extract and chilli or garlic extract can be sprayed on the foliage to control the pest. Apply NPV 250 LE/ha with Teepol 0.1% and Jaggery 0.5% thrice at 10-15 days interval commencing from the flowering stage. Apply Neem oil or Pungum oil 80 EC @ 2ml/lit.
Always consider an integrated approach with preventive measures together with biological treatments. If more than 2 larvae are found per 10 plants, control measures must be started. Chlorpyriphos and Quinalphos are suggested to reduce semilooper population.