Xenocide

The ethical problem is stated in the premise. Lusitania is home to three species whose survival depends on one another: human beings, the native pequeninos and the Hive Queen, and the descolada virus is simultaneously lethal to humans and necessary to the pequeninos' development. That interdependence is what makes the planet worth saving and impossible to leave alone.

Against that, the Starways Congress has decided that the risk of the virus spreading justifies destroying the planet and everyone on it, and a fleet is already on its way. The title refers to the killing of an entire people, and the novel's question is whether a second xenocide can be prevented, which is why the book is read as the point where the series becomes a study of political decision-making rather than of combat. The book was published in 1991 as the third in the sequence, and it takes in material from a shorter story the author published earlier the same year. Its concerns are communication and the fear of difference, which is why the political decision and the life of the settlement on Lusitania are treated as the same kind of problem.