For the best results with those infestations, start by getting your hands on incendiary bolts since they're really efficient with kerosene, using just 3 bolts per can. While you're working towards unlocking those, keep an eye out for propane tanks and other explosives near the nests, since you can trigger those from safely far away to take out multiple nests at once.

When you're forced to use molotovs, try to position yourself at maximum throwing distance, and look for opportunities where nests are clustered together in places like bridges or warehouses. That way, you can sometimes get two or three with one throw which is a huge help for conserving resources. Night raids are actually pretty effective too, since fewer freakers tend to pop out of the nests after dark, though you'll want to watch for roaming hordes.

Something that helps a lot is parking your bike at a good angle for a quick escape after you light up a nest. The red zones on your map will show you where the infestations are, and they often bunch up in predictable spots like bathrooms and under bridges. Getting these cleared out is definitely worth the effort since it'll make the area safer and open up fast travel options, assuming you're not playing on survival mode.