Onion Caterpillar (Cutworm)

📖 Description

Onion Caterpillar (Spodoptera exigua), also called Beet Armyworm, is a polyphagous pest of onion, cotton, vegetables and other crops across the Indian subcontinent, particularly severe in onion belts of Maharashtra (Nashik, Ahmednagar, Pune), Gujarat, Karnataka, Andhra Pradesh, Telangana, Tamil Nadu and Madhya Pradesh where onion is grown on over 1.2 million hectares. The pest is a generalist feeder attacking over 50 plant species including onion, garlic, cotton, tomato, chilli, cabbage, soybean and many weeds. Young larvae feed gregariously on leaf undersides creating characteristic ‘window-pane’ damage, while older larvae disperse and feed individually, completely skeletonizing leaves. The pest is particularly damaging in onion because larvae often feed inside the onion ‘neck’ (where leaves emerge from bulb), causing rot and bulb loss. Beyond direct defoliation, the pest is a vector of some plant viruses. Outbreaks are favoured by warm dry weather, weedy fields and continuous cropping. The pest has developed resistance to virtually all major insecticide classes (organophosphates, pyrethroids, carbamates, even some Bt toxins), making resistance management critical — rotate across modes of action and use NPV (SeMNPV) which is highly specific to Spodoptera and very effective. IPM with pheromone trapping of males, Bt and NPV applications against early instars, hand-collection of egg masses and gregarious larvae, and need-based insecticide rotation provides effective control. The pest is most severe in weedy fields — maintaining field sanitation is a key preventive measure.