Is the leaf curl in my chilli (mirchi) from mites or thrips, and how do I tell?

Getting the cause right matters because the treatment differs. Thrips usually cause leaves to curl upward with a silvery, crinkled look and you may see slender insects when you tap a leaf over paper. Yellow mite causes the leaves to curl downward and become narrow, elongated and leathery with a downward cupping, and the mites are tiny and need a hand lens to see. Virus leaf curl, spread by whitefly and thrips, gives stunted plants with puckered, mosaic, distorted leaves and does not improve even after the insects are controlled. So inspect with a lens, note the direction of curling and whether plants are stunted, and ideally show samples at your KVK or use a plant clinic for confirmation. Once identified, use the recommended miticide for mites or insecticide for thrips per label, while virus is managed only by controlling the vector and removing infected plants.