Good to hear that you make use of what does want to grow locally. Totally sensible. I've heard insect pressure in the tropics can be off the charts. They're like superhappy with all the sun, totally energized to eat whatever and multiply, multiply. Hard to battle and heartwrenching to see them in action i'd think. I mostly have snails to beat, but they come in waves eating weak plants, i just resow in between waves. Saving seeds gives me that luxury to do that for free and bit by bit my plants seem to adapt to them. I saw one on top of a newly salad, he was "sniffing" it out and decided to move on. That was a good day. I don't know if coming year will be similar. Nature can be so eratic and hard to pin down.
That's why i'm grateful to be part of this community where we can freely exchange information and together creep forward at our own pace to hopefully obtain sustainability and a new balance and way of life with the land. A copyable template for future generations to build on where ever we live. It's where my energy lies anyway, sorry to bother you with it. Haha.
I respect you've moved away from growing melons if it's so difficult and you don't want to be part of a system using pesticides. In the adaptation gardening community we're trying to do similar, using as little inputs as possible by trying different genetics and not being afraid of hybridizing siblings. Breeding the fittest/tastiest/most resistant varieties we can in differing settings like mountains, marshes,high up north to islands and forests or the opposite deserts like situations.
Leaving you with some pics of watermelon seeds and what people grew this year.