I lived almost my whole life in tropical areas (Central America), so I can give you a tip or two about that!
First of all, the advice given above is really accurate. I would recommend you to travel will long pants and long-sleeve shirts. The military type you say is actually the one I use, since the fabric is very thick and protective. Use light colors to keep body temperature low. Most tourists I see on tropical areas wear very fresh (exposed) clothes because of the warmth, but that is a mistake. The reason is, you got it right, the insects. Mosquitoes ARE an issue on the tropics. So I prefer to be a little bit warmer and bite-free than the other way around. Also pack a jungle hat so protect against the sun, like this one: http://www.endicotts.co.uk/images/sf_d.p.m_jungle_hat_02.jpg
I also recommend wearing boots (jungle specific boots). They will protect your ankles when walking through uneven/slippery terrain and against insects.
Be sure to have your photo gear packed in weather-proof cases/bags. I don't know how's the weather on those places on January-February, but if it is a tropical rain forests, rain (HEAVY rain) is something to consider.
Pack extra batteries, specially if you are going to remote places, and extra food and water. If you can get some of those water-purifying pills, pack some of them, just in case.
I also like to disable all sounds of the camera when going to these places where you expect to photograph wild animals. These animals are very elusive, and get scared with the slightest sound (like the beep of the camera telling you it auto-focused correctly).
And the most important of all... post some pictures when you get back! That trip you are about to make is one I've been planning for some time...