Looks like a cottony cushion scale infestation to me. Also on the leaf in the background I see some brown scale along the center of the leaf. Those white and brown spots are actually the pest, and they secrete that sappy sticky fluid as they consume the liquids from your tree. If its a light infestation and you have a pretty small tree just take a cotton ball soaked in isopropyl alcohol and lightly brush it on the infested spots. The scale will let go instantly and die from the alcohol. Otherwise you can use neem oil to control, some people are using rosemary oil now too, with reportedly good results. Do a search on the forum for scale and you should get some better pointers. -Mike B

Lamocan, sounds like some type of insect..check for spider mites, aphids and scale. Mites are difficult to detect..but when a plant is infested, you'll spot fine-looking webbing usually between leaves. If the hibiscus isn't too large, is there a way you can hose it down? Toni

The "small black objects" could be Aphids, which come in many colors not always just green. The first step, besides trying to identify which insect this is, is to knock them off the plant with a sharp stream of water and that can be done with a hand held sprayer instead of your garden hose which can severly damage your plant.

Check for scale or aphids. The sticky substance sounds like honeydew, either on the Mango itself or dripping from a nearby plant.