Comment by cmpb

Don't stop there: fungi and beetles are some other stressors that could be modeled alongside caterpillars using similar techniques. Like lepidopterans, they are very host-specific, though they have somewhat different transmission vectors, so you could see the defoliation (or other foliage impacts like leaf curling and yellowing) spread / not spread depending on factors such as proximity, moisture, wind and the parasite's lifecycle.