Answer: Not all insecticides are safe to use on all plants. Mandevilla is especially sensitive to the oils in pesticides, as you have discovered. The good new is that mandevilla responds well to pruning. I would trim the plant to remove the damaged stems and leaves (and the insect pests, too). If you see more insects, try washing them off with plain water. You can also collect some of them in a plastic baggie and take them into your local cooperative extension office or well staffed nursery for identification. Once you know what the pest is you can determine what will control it without harming your mandevilla. Best wishes with your plant!
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