The tower and the hive - Anne McCaffrey

In this, the fifth book in the Tower and the Hive series, the children of Damia and Afra Lyon take up new and demanding responsibilities - trying to discover the whereabouts of all the Hiver-occupied worlds. For the Hivers are still a terrible threat and can bring total annihilation to both humans and their furry allies the Mrdini unless the remaining Hiver Queens can be prevented from further colonization. And a startling additional problem has arisen with the Mrdini. No longer dying as drastically as they once had in their ceaseless struggle against the Hivers, they face a serious population explosion and need the help of the Medical Prime Zara Lyon.