AbstractMales of haplodiploid species develop from unfertilized eggs. An unmated female, or a female in some other way prevented from fertilising eggs, is thus still able to produce male offspring. The presence of females constrained to produce only male progeny distorts the population sex ratio and leads to selection on unconstrained females to produce a daughter‐biased sex ratio. With panmictic mating, the response of unconstrained females maintains a population sex ratio of equality. In populations with strong local mate competition, the presence of constrained females has only a minor affect on the sex ratio of unconstrained females. If unconstrained females modulate their sex ratio in response to all‐male oviposition, there is still no penalty to the production of all‐male broods as constrained oviposition becomes more common, providing less than 50% females are so constrained. When there is local mate competition or if there is no sex ratio response by unconstrained females, there will be unequal costs and benefits to all‐male production, some of which are discussed. The paper also contains a review of the factors leading to constrained oviposition in parasitic wasps and a discussion of how the percentage constrained oviposition can be measured in natural populations.