I can see you have mealybug infestation from the second picture. The ants are there because they love the honeydew secreted by the mealybugs. They will protect the mealybug from its natural predator. Easiest way to get rid of the infestation is with imidacloprid (Provado, Merit etc).

I am not sure about the 1st picture. It could be mealybugs or mango scale. If it is the latter, just spray them with mineral oil + soap or brush them off with a toothbrush.

Hope that helps

The white sticky mounds are the housing for cochineal bugs (also known as mealy bugs.) Spray with insecticidal soap or unscented dish soap.

Mealy bugs cause damage by sucking the juice from their host plants
and excrete the excess sugars as a substance called honeydew.

The affected leaves turn yellow and eventually drop from the plant.
They also cause fruits, vegetables, and flower buds to prematurely drop
off. In a bad infestation, their waxy excretions encourage the
development of sooty mold fungus which completely destroy the plant.

1. You will notice a fluffy white wax produced in the leaf axils or on the stems and branches of the plant.
2. You will notice an accumulation of honeydew which makes the plants
   sticky and encourages the growth of sooty molds, giving the leaf and
   stem surfaces a blackened appearance
3. Due to infestation you will notice that the plant as lost its vigor
   and the leaves start to turn yellow and eventually drop. As a result,
   plants may be stunted, or even killed
4. Infested plants will stop growing, and will have a very depressed
   shrivel look like as though you have not watered them for days.
5. You will see a trail of ants around your garden and on the plants.
   Ants breed and protect mealy bugs for their honeydew secretions and may
   help to spread them through the collection. The ants protect the mealy
   bugs from their natural enemies such as small wasps that act as
   parasites on the mealy bugs and from predators such as ladybugs. The
   presence of the ants is very important to the mealy bugs’ survival, and
   elimination of the ants using poisonous ant baits, will usually mean the
   destruction of the mealy bug colonies.

Avoid chemicals if you are environmentally conscious. Imidacloprid is toxic to beneficial insects (bees, lacewings, etc.). Try removing as much mealy bugs as you can with a Q-Tip dipped in alcohol, then apply insecticidal soap periodically till bugs disappear. Make sure to do it early in the morning o late in the evening, and rinse soap with a water spray before leaves and stem dry.

I am having a problem that I have not seen in any of the forums I have visited. I grow mango trees from seeds to plant around my neighborhood that is in need of shade trees. I do not expect to get any fruit from theses trees. All went well for several years but recently some pest has found them. What appears to be happening is that the new leaves get almost totally eaten before they reach maturity. There is no sign of any bugs or ants so I do not know what is eating the leaves. The entire leaf is not eaten. The part near the stem is left. See the attached photo. Anyone have any ideas as to what is ratings my trees and how to get rid of the pest.

apaul: Sprinkle the base of the tree with and the infested area with diatemacious earth. I had the same issue with my yard long bean stalks this summer . It was infested with so many ants and similar mealy bugs. I only sprinkled the base of the bean stalks, and I was very careful to not get it wet when I water the plant in the area that was sprinkled with diatemacious earth. It works for me. I don't see any more ants climbing up the bean stalk and black mealy bugs started to disappear.

pqmccutcheon: I think it's weevil. I had the same issue with my citrus, bean,herbs. I got flashlight at night to go check and saw it was weevil. I sprinkle diatemacious earth on the herbs and no longer have wholes and leaves missing anymore. The citrus are doing much better too. As a matter of fact, I'm going out there right now to check with flashlight for the weevil.