Answer: It sounds like budworms. The eggs will hatch into little worms which will chew through the sepals of the flowers and consume the insides of the flower buds. Then they will exit and pupate in the soil. The best defense is to hose or wipe off any eggs you see - before they hatch. You can spray the buds with Bt (bacillus thuringensis) as an added protection. Bt is a bacterium which acts as a stomach poison so the larva must eat it in order for it to be effective. But if they eat it on their way into the flower bud, they will die before completely consuming the undeveloped flower. Bt is sold as Dipel in garden centers and it is harmless to other insects and wildlife. To help prevent next year's generation of budworms, cultivate the soil beneath your hibiscus and petunias to expose pupating larvae to the elements and to other insects.
Best wishes with your garden!
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