Flies in Evolutionary Flight
Most insects are specialists. ~ American biologist Andrew Forbes
Herbivorous insects are the most speciose animal group. Speciation is driven by 2 pressures: food and foes – plants and predation. Overbearing overlap on the same food source is a formula for shortage. Moreover, plants adapt to put the hurt on overpowering predators. Better to find something to eat that is not in high demand.
The tropics are full of flies; so many different flies; each species nibbling on a different plant.
The tropics are also full of parasitic wasps, specialized to lay their eggs in a specific fly. Larval offspring will not survive if a wasp lays its eggs in the wrong species.
As each fly is targeted by a specific wasp, changing food source lets a fly escape its nemesis, at least until the wasp finds it again, or another wasp adapts to take advantage. It is an evolutionary game of hide-and-seek, driving dodgy diversity amid the verdure allure.