The typical knee-jerk reaction of the novice gardener is to wage war against even the smallest of pest invasions. Fortunately the major fruit tree crops here don't require pesticides. Fungicides are helpful though, especially for mango. But if you don't require a clean looking fruit, then you can even bypass that (with some reduction in crop size).
As buddy green mentioned, providing a healthy soil environment is the first step in disease / pest defense. A healthy / vigorous tree can outgrow damage from pests like the sri lankan weevil. I also added compost to my soil, in the form of several hundred cubic yards of tree trimmer mulch, and it's had a very positive impact.
But, at the commercial level, where the goal is to make enough profit to pay for land, input, and labor costs (and have some left over), maximizing production by using pesticides (whether organic or conventional) only when necessary is probably a necessary evil.