An asexual strain of Lysiphlebus fabarum (Hymenoptera: Braconidae) gains fitness in superparasitised hosts, but a sexual strain pays costs

Abstract

Abstract. 1. The fitness impacts of two levels of superparasitism were compared in a sexual and an asexual strain of Lysiphlebus fabarum (Marshall) developing in black bean aphids.2. Asexual females were larger than sexuals, had higher eggs loads, and better adult emergence in two of three treatments, but parasitised fewer available aphids in 24 h (80% fewer when foraging alone).3. Superparasitism resulted in wasps that were larger than those emerging from singly parasitised aphids, and asexual females had larger ovaries, without delayed development. In contrast, sexual wasps took about 2 days longer to develop in superparasitised hosts, and females had smaller ovaries with lower egg loads.4. The growth of host aphids bearing asexual larvae was not reduced relative to healthy aphids, except when heavily superparasitised, whereas sexual larvae reduced aphid growth in all treatments.5. Elimination of supernumerary larvae was virtually complete at 4.5 days after parasitism by sexual females, but no elimination occurred among asexual larvae. The evolution of diminished aggression in asexual larvae may be facilitated by greater genetic similarity, without necessarily leading to gregarious development, assuming the extended life of supernumeraries somehow improves survivor fitness.6. Sons of virgin sexual females developed faster than sons of mated females, implicating parental effects that slowed development of the latter.7. It is concluded that asexual females of this strain use superparasitism to improve host quality, and thus the fitness of their daughters, whereas females of the sexual strain prioritise offspring number.