I thought one of the big points was there's no M. structor females on the islands.
M. Ibericus produces 4 kinds of offsprings.
1. M. Ibericus queen + no male (unfertilized egg) -> M. Ibericus male.
2. M. Ibericus queen + M. Ibericus male -> M. Ibericus queen
3. M. Ibericus queen + M. Structor male -> M. Structor male, no genes from the mother
4. M. Ibericus queen + M. Structor male -> M. Structor/Ibericus hybrid female, (worker ant, infertile)