Precise Sex Allocation, Local Mate Competition, and Sex Ratio Shifts in the Parasitoid Wasp Trichogramma pretiosum

We determined the sex, order, and clutch size of eggs laid by the parasitoid wasp, Trichogramma pretiosum Riley, in the eggs of one of its natural hosts, Trichoplusia ni (Hübner). The parasitoid allocated sex non-randomly to hosts in the laboratory with a variance significantly less than that of a b...

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Bibliographic Details
Published in:Behavioral ecology and sociobiology 2001-03, Vol.49 (4), p.311-321
Main Authors: Luck, R. F., J. A. M. Janssen, J. D. Pinto, E. R. Oatman
Format: Article
Language:English
Subjects:
Animal and plant ecology
Animal, plant and microbial ecology
Animals
Autoecology
Biological and medical sciences
Eggs
Female animals
Fundamental and applied biological sciences. Psychology
Insect eggs
Laboratorium voor Entomologie
Laboratory of Entomology
Male animals
Mating behavior
Noctuidae
Parasite hosts
Parasitism
Parasitoids
PE&RC
Protozoa. Invertebrata
Sex allocation
Sex ratio
Trichogramma pretiosum
Trichogrammatidae
Trichoplusia ni
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Summary:We determined the sex, order, and clutch size of eggs laid by the parasitoid wasp, Trichogramma pretiosum Riley, in the eggs of one of its natural hosts, Trichoplusia ni (Hübner). The parasitoid allocated sex non-randomly to hosts in the laboratory with a variance significantly less than that of a binomial (random) distribution, our null model. More clutches of two or more eggs contained a single male egg as the second or third egg laid than would be expected by chance and none contained two or more male eggs. T. pretiosum also increased the sex ratio (% male) of its offspring with increasing foundress numbers by increasing the frequency of male offspring as the second egg in a two-egg clutch allocated to unparasitized hosts and as the single egg allocated to previously parasitized hosts. These results indicate that T. pretiosum allocates the sex of its offspring precisely. Precise sex allocation is favored under local mate competition because it reduces variation in the number of sons per patch thus maximizing the number of inseminated daughters emigrating from the patch. Similar combinations of female and male offspring emerged from T. ni eggs parasitized by T. pretiosum in the field, again with a sex ratio variance less than that expected for a binomial distribution. These results strongly suggest that this parasitoid species manifests local mate competition.
ISSN:0340-5443
1432-0762
DOI:10.1007/s002650000294