What type of reproduction system in parasitic hymenopterans results in all females?

The correct answer is thelytoky. This type of reproduction is characterized by the production of offspring that are all female, typically without the involvement of males. In thelytoky, unfertilized eggs develop into females. This reproductive strategy is particularly advantageous in stable environments where the existing female population can effectively exploit available resources and reproduce without the need for mating.

In contrast, arrhenotoky, which is another form of reproduction observed in some parasitic hymenopterans, results in the development of males from unfertilized eggs while fertilized eggs develop into females. Epitoky refers to a method of reproduction usually associated with polychaete worms, involving a specific phase of maturation leading to reproductive capability, and does not pertain to hymenopterans. Autotoky is a term not commonly used in the context of hymenopteran reproduction, as it focuses on a broader phenomenon of asexual reproduction. Thus, thelytoky clearly defines the mechanism by which parasitic hymenopterans produce only female offspring.