Local mate competition and precise sex ratios in Telenomus fariai (Hymenoptera: Scelionidae), a parasitoid of triatomine eggs |
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Authors: | Jorge E Rabinovich Martín Torres Jordá C Bernstein |
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Institution: | (1) Laboratoire de Biométrie et Biologie Evolutive, UMR CNRS 5558, Université Claude Bernard-Lyon 1, 43 Bd. du 11 de Novembre 1918, 69622 Villeurbanne Cedex, France e-mail: carlosbe@biomserv.univ-lyon1.fr Tel.: +33-4-72431438, Fax: +33-4-78892719, FR;(2) Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón II, Ciudad Universitaria, (1428) Buenos Aires, Argentina, AR;(3) Departamento de Parasitología y Microbiología, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155, (1121) Buenos Aires, Argentina, AR |
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Abstract: | Telenomus fariai is a gregarious endoparasitoid of the eggs of several species of Triatominae (Hemiptera) with a high degree of sibmating:
males fertilize their sisters inside the host egg before emergence or emerge first and copulate with their sisters as these
emerge. Our results show that, when laying alone, T. fariai behaves adaptively, minimizing offspring mortality and conforming to the prediction of local mate competition (LMC) theory
by laying a single male, which is sufficient to fertilize all the sisters. When more than one wasp was placed with one host,
sex ratios still conformed to LMC predictions but, despite the decreasing number of eggs laid per wasp, clutch size could
not be completely adjusted to avoid mortality. This is not surprising, as superparasitism is rare in the field. Offspring
production was independent of the contacts between conspecifics but was affected by the number of mothers laying on a single
host egg. The sex of the progeny was precisely determined: a female produced one male per clutch when laying on both unparasitized
or previously parasitized hosts. On the other hand, a mother produced less daughters when superparasitizing. Under crowded
conditions, the number of eggs laid per female wasp and per host decreased as the number of mothers increased. Developmental
mortality also increased with the number of T. fariai eggs per host, determining a maximum of approximately 14 emerged adults. Host resources per individual affected male and
female adult size with similar intensity, and male adult mortality was slightly higher than that for females. These results,
and previous findings, suggest that T. fariai attains Hamiltonian sex ratios by laying one male and a variable number of females, and that the detection of chemical marks
left by conspecifics provides information on the number of foundresses sharing a patch.
Received: 4 February 2000 / Received in revised form: 19 April 2000 / Accepted: 20 May 2000 |
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Keywords: | Telenomus fariai Scelionidae Local mate competition Sex ratio Evolutionarily stable strategy |
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