Mealybugs damage hibiscus plants by sucking the plant's juice, usually from the foliage. You may not notice light mealybug infestations, as just a few leaves may be affected. As more mealybugs occupy the plant, however, it may shrivel noticeably and can die if you do not get rid of the mealybugs. According to Planet Natural (ref. 1) mealybugs can damage plants another way as well. They leave behind a residue, called honeydew, which offers an ideal environment for sooty moulds. Controlling a mealybug infestation is essential for hibiscus plants' survival.
Spray the hibiscus with insecticidal soap, making sure to cover all the mealybugs you can see. These bugs may live anywhere on the hibiscus, but also check carefully under each leaf where the bugs may cluster.
Put on rubber gloves. Dampen a paper towel and wipe the mealybugs off of the hibiscus.
Squash the removed bugs or place them in a plastic bag to hasten their death, if they are still alive.
Spray the plant again with the insecticidal soap to kill any larvae, eggs or adult mealybugs you may have missed.
Inspect the hibiscus daily for any signs of mealybugs. Re-treat the plant by spraying with insecticidal soap if necessary.
Check all plants near the hibiscus for signs of mealybug infestation and treat them at the same time that you treat the hibiscus. This will help prevent reinfestation.