Male altruism and wing polymorphism in a parasitic wasp

Males ofTrichogramma sp., a gregarious parasitoid which attacks eggs of the yellow-legged tussock mothIvela auripes (Lepidoptera: Lymantriidae), are polymorphic for wings. In mating within host eggs, no difference in mating success was observed between winged (large) males and wingless (small) males, whereas in mating outside eggs, the former were superior to the latter. Some wingless males were observed to perform sneaking copulation on egg masses. In the 1-male brood, which is thought to be founded by 1 mother wasp, the male size tended to decrease as the number of females per brood increased. But in the 2-male brood, which is assumed to be added with 1 more smaller male produced by the second mother wasp in double parasitism, the larger male did not reduce his size, compared with the male of the 1-male brood with an equal number of females. This phenomenon can be explained reasonably by a version of the kin-selection theory: When there is only 1 male in a host egg, he transfers resources in the egg to his sister females, but, when another male appears, he decides to act to the females less altruistically.