The origin of soldiers in the gall-inducing thrips of Australia (Thysanoptera: Phlaeothripidae)

Abstract  For 7 of the 23 described species of Australian gall-inducing thrips, the first individuals of the foundress' brood to eclose are gall-bound soldiers, which are morphologically and behaviourally specialised for defending the fully winged dispersing brood. Additional support is provided for the hypothesis that these self-sacrificing soldiers evolved only once and that there have been two subsequent reversions to a solitary life. Furthermore, this single origin of eusociality took place approximately six million years ago and perhaps four million years after the origin of gall induction in the Acacia thrips. The two losses of the soldier caste may have happened at very different times. One loss may have occurred very soon after the origin of soldiers (approximately 300 000 years later), and the other may have occurred another three million years after that.