, Volume 136, Issue 3, pp 365–373 | Cite as

Superparasitism and sex ratio adjustment in a wasp parasitoid: results at variance with Local Mate Competition?

  • Serena Santolamazza-CarboneEmail author
  • Adolfo Cordero Rivera
Population Ecology


Anaphes nitens is a solitary parasitoid of the egg capsules of the Eucalyptus snout beetle, Gonipterus scutellatus. Some traits of its natural history suggest that Local Mate Competition (LMC) could account for sex ratio adjustment in this species. We tested whether males emerged early, a prerequisite for fully local mating, and investigated the occurrence and effect of superparasitism on adult size and pre-emergence mortality, factors that might influence sex ratio adjustment. We found in field-collected egg capsules that males emerged first. To investigate the effects of superparasitism on adult size, we compared the sizes of parasitoids that emerged early and late from egg capsules collected in the field, and from egg capsules parasitized and superparasitized in the laboratory. Superparasitism reduced parasitoid size, affecting females more strongly than males, and increased pre-emergence mortality. We estimated A. nitens sex ratio and parasitism rate in the field during 2 years in five localities and during 4 years in a sixth. Following LMC we expected an increase in sex ratio (proportion of males) with increasing parasitism rate (assumed to reflect parasitoid density). We found that sex ratio decreased from 0.38 when the parasitism rate was low (0–20%) to 0.21 when parasitism was high (80–100%). In contrast with field results, a laboratory experiment showed that: (1) at a low parasitism level sex ratio was clearly female biased (0.28±0.04), (2) at a high parasitism level sex ratio increased (0.40±0.07), (3) male larval survivorship was not lower than female survivorship, and (4) low-quality hosts (i.e. superparasitized) were allocated more males. We conclude that LMC cannot explain the sex ratio adjustment observed in the field, even at low parasitism rates, and alternative explications for highly female-biased sex ratios must be found. One such alternative is female-biased dispersal.


Anaphes nitens Body size Host density Mymaridae Pre-emergence mortality 



We are grateful to David J. Thompson for his revision of English on a previous version of this manuscript. Funding was provided by the Spanish Ministry of Education and Culture as a doctoral grant to SSC, and as research grants to ACR (DGES PB97–0379) and Cátedra Filgueira Valverde, Universidade de Vigo.


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Copyright information

© Springer-Verlag 2003

Authors and Affiliations

  • Serena Santolamazza-Carbone
    • 1
    Email author
  • Adolfo Cordero Rivera
    • 1
  1. 1.Grupo de Ecoloxía Evolutiva, Departamento de Ecoloxía e Bioloxía AnimalUniversidade de VigoPontevedraSpain

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