January 2013. A caterpillar making large round holes in cucumber leaves in the Maldives. The question was, is this Helicoverpa armigera?

The reply from one member was no, it looks more like Spodoptera litura. They are usually found large numbers when in an earlier stage. Plenty of information on this on the Internet. See references from ICRISAT and All India Pulses programme for its management: integrating pheromone trap monitoring, insect pathogen distribution and biocontrol by generalist predators such as Coccinellidae = ladybird beetles, but also including drongos, cattle egrets and other insectivorous birds.