Sex allocation of three solitary ectoparasitic wasp species on bean weevil larvae: Sex ratio change with host quality and local mate competition

Abstract

Sex ratio manipulation by ovipositing females was surveyed in 3 solitary ectoparasitic wasp species, Dinarmus basalis (Pteromalidae), Anisopteromalus calandrae (Pteromalidae), and Heterospilus prosopidis (Braconidae), that parasitize azuki bean weevil (Callosobruchus chinensis (L) (Coleoptera: Buruchidae)) larvae within azuki beans (Vigna angularis). Variables were local mate competition (LMC) and host quality (HQ). We used host age as a measure of host quality (from 9- to 16-day-old hosts), changed the number of ovipositing females to control the level of local mate competition (1 female and 10 females), and examined oviposition patterns of the wasps. The offspring sex ratios (proportion of females) of the 3 wasp species respond qualitatively same to HQ and LMC. The common qualitative tendency among the 3 species is an increase of sex ratios increase with host age. In the process of changing the sex ratio (9- 13-day-old) 3 wasp species respond only to HQ. In the hosts that end development in size (14-16-day-old) wasps respond to LMC. The response of sex ratio change to LMC in the old host age-classes are different among the 3 species. In the situation that there exists LMC (10 females) sex ratios are the same among the 3 wasps. However, the sex ratios in no LMC (single female) are heterogeneous among the 3 wasps.