Answer: It sounds to me as though leafminers have been busily at work within the leaves of your nasturtiums. These are the larva of a fly. The female makes a little opening in the leaf to deposit her egg and when the worm hatches it tunnels around between the upper and lower surfaces of the leaf. When it has finished feeding it makes an exit hole and goes down into the soil to pupate. It emerges as an adult to mate and lay eggs. Pinch off the affected leaves and squish them to stop the critters in their tracks. You can also place a layer of mulch over the soil to keep any insects hiding there from emerging and attacking your plants again. Your plants should continue blooming, even with a leafminer problem.
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