I Find Two Closely Related Species of Fly, One (P)

I find two closely related species of fly, one (P) of which appears to reproduce parthenogenetically while the other (S) reproduces sexually. In the same location, I find a bizarre third kind of insect, a sterile defensive form with enlarged mandibles. Because it is sterile, I conclude this form must be produced by either P or S. Which of the following explanations is the MOST likely for the origin of the sterile defensive flies?

A) P because they reproduce parthenogenetically and this increases their relatedness and likelihood of kin-based altruism to other P individuals in the colony.
B) P because they reproduce parthenogenetically and the third type is sterile. Sterility may be a by-product of parthenogenesis.
C) S because they reproduce sexually and this increases their relatedness and likelihood of reciprocal altruism to other S individuals in the colony.
D) S because they reproduce sexually and the third type is sterile. The sterile individuals are altruistic (defending all members of the group) .