Insects
Do not use Malathion liquid to control insects. The oil "carrier" in Malathion will cause the leaves to drop and may even kill the plant. WP (Wettable Power) Malathion is fine. Most insect problems (aphids, spider mites) are best handled by spraying underneath the plant's leaves with a hard stream of water at relatively close range. Careful observation and persistence are necessary to keep the insects at bay.
To control severe infestations of mites and/or whitefly, soap sprays are recommended. Use Insecticidal Soap according to the label. Use Palmolive or Dawn or Sunlight soap at one to two tbs. per gallon to smother the insects on the plants. If you need to use more than 2 tbsp/gal, remember to later rinse off the plant. Spray twice a week until bugs are gone.
There are occasions when chemical sprays seem to be the only way to stop a major infestation. Should you choose to use chemicals, follow directions carefully and use with caution. Although few insecticides injure hibiscus, it is always good to read labels and to see if the product is recommended for hibiscus.
Spray your plants in the evening after the heat of the day or very early in the morning. This applies to both using insecticides or foliar feeding. There is less danger this way of burning the leaves.