Tom Bradman & Tony Bradman 
Bug Wars [PDF ebook] 

Trapped on a colony spaceship ever since Planet Earth became too
polluted to support human life, Luke whiles away his time playing computer games, just like any
normal boy. But when an alien battleship arrives demanding that Luke
comes aboard, it seems that his computer-whizz gaming skills have been
mistaken for genuine warfare! The aliens are determined to wipe out their enemies, and Luke either has to help defeat them, or
die! Does Luke have the skill it takes to beat the bugs and survive?