Legoguerin since you didn't use the Quote button we don't know what you're responding to when you say "Oh no!"
As long as I'm here, now that I've lived here a while, I will add some info that I've learned.
1) bringing in seeds. I "know someone" who's done it many times with no problems at all. They don't even have to be hidden, in fact I think it's best just to scatter them around in various places in various pieces of luggage. IMHO.
Many things are not available here and that's why people bring them in. They never heard of kale where I live. They don't have lavender or certain chili peppers or giant sunflowers or numerous other things one may want including certain varieties of tomatoes or etc veges ...
2) Leaf cutter ants. Mirex works sometimes but not always. Some won't carry it back to the nest. Somehow they know better.
There is NO magic bullet to kill leaf cutters that I have heard of. Sure you can dynamite them and burn them out but more will come. It's a constant battle if you live in certain areas.
Just because Costa Rica in general uses a lot of chemicals on food and weeds and has bad environmental practices in many places, that doesn't mean you can't or shouldn't do better and teach the locals better practices. Yes they use roundup indiscriminately because they don't know better. Teach them a better way and explain why. Yes they drain black water into the rivers and ocean, so educate them as best you can why that's bad.
Nothing against Ticos but the truth is they just are not well educated in general, especially regarding things like chemicals in foods (preservatives, pesticides etc) and protecting the water and soil and air. They're better than they were though so progress is happening, it's just slow.
Where I live, when we don't use certain foods because of the preservatives they look at us like we're crazy. They have never thought of reading the labels for such things, or to avoid sugar in orange juice or canned corn for example. BPA, forget it!
They are learning. Now I see some organic markets and organic vege vendors at the farmers market. Health stores are popping up. But they have a long way to go and yes they use tons of chemicals on crops and weeds.