Harvesting Terra

They came, they harvested, they conquered, leaving few oxygen-breathing creatures on the face of the planet. The advanced insectile-like race then disseminates a vast biomass of oxygen producing plants to alter the environment in preparation for the coming of the mother ships. Advance scouting missions rid Earth of toxic waste as more scouts usher clouds to irrigate plants that voraciously expand to blanket the planet.
In a hair-raising struggle to survive, three young protagonists, Tavis, a brainiac with a sense of purpose, Dana, not yet a teen with the compassion of a nightingale, and Bree, a tempestuous Amazonian-like goddess band together and seek sanctuary in Las Vegas, then watch as alien scouts methodically disintegrate the city. Although they are generally ignored in their excursions, they soon realize they won't survive in harmony with the aliens as the vast transformation of the planet continues. With vivacity amid burgeoning romance, they resolve to confront the reality that survival will require outsmarting the aliens and risking their lives in the process of making Earth a place the aliens can't live.