Reproductive strategy of Dinarmus vagabundus Timb. (Hym., Pteromalidae): real sex ratio, sequence of emitting diploid and haploid eggs and effects of inbreeding on progeny

Abstract

One ovipositing adult female D. vagabundus will give rise to three females and one male on the average. In order to test the hypothesis of the preferential death of one sex, we experimentally determined if the sex ratio at ovipositing was the same as that of the emerging adults. Newborn larvae were used after first determining that their number was the same as that of the eggs deposited. When six larvae were transferred to a paralyzed host, there was no selective elimination of larvae by competition between sexes, since all developed up to the adult stage. The sex ratio observed at emergence of the adults was thus the same as that at ovipositing. The emission sequence of haploid and diploid eggs showed that the majority of the first eggs oviposited are fertilized, the haploid eggs being emitted last. Mating between genetically close D. vagabundus parents occurs with 60 to 89 % of the females. The productivity of females after six generations of sibling crosses was unaffected and there was no significant change in the sex ratio of the progeny. Résumé Stratégie reproductive chez Dinarmus vagabundus Timb. (Hym.; Pteromalidae): taux‐sexuel réel, sequence de ponte des oeufs diploïdes et haploïdes et effets de la consanguinité sur la descendance Chez D. vagabundus en présence d'une seule femelle pondeuse, il émerge en moyenne 3 filles pour 1 fils. Pour tester la validité d'une mort préférentielle d'un sexe sur l'autre, nous avons expérimentalement analysé si le rapport des sexes à la ponte correspondait à celui des adultes émergés. Nous avons expérimenté avec des larves néonates estimant que leur effectif correspondait à celui des oeufs pondus. Quand six larves néonates sont transférées sur un hôte paralysé, il n'y a pas une élimination sélective des larves par compétition entre sexes puisque toutes se développent jusqu'au stade adulte. Le taux sexuel observé à l'émergence des adultes correspond au taux sexuel à la ponte. L'observation de la séquence de ponte des oeufs haploïdes et diploïdes montre que les premiers oeufs pondus sont dans la majorité des cas fécondés; l'oeuf haploïde étant pondu en dernière position. Chez D. vagabundus, les accouplements entre parents génétiquement proches affectent de 60 à 89 % des femelles. Examinée sur 6 générations, la productivité de ces femelles n'en est pas affectée et il n'y a pas de variation significative du taux sexuel. Zusammenfassung Zur Reproduktionsstrategie von Dinarmus vagabundus Timb. (Hym., Pteromalidae): reales Geschlechterverhältnis, Reihenfolge der Ablage diploider und haploider Eier und Wirkungen von Inzucht auf die Nachkommen Aus der Eiablage eines Weibchens von D. vagabundus gehen Nachkommen mit einem Geschlechterverhältnis von i.M. 3:1 zugunsten der Weibchen hervor. Zwecks Untersuchung der Hypothese über den vorzugsweisen Tod eines Geschlechts wurde experimentell geprüft, ob das Geschlechterverhältnis zur Eiablage mit jenem der Nachkommen‐Adulten übereinstimmt. Die Zahl frischgeschlüpfter Larven erwies sich als gleich mit jener der abgelegten Eier. Wen...

Sex determination in the hymenopteran Diadromus pulchellus (Ichneumonidae): validation of the one-locus multi-allele model

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Insemination Capability of Male Pteromalus Venustus (Hymenoptera:Pteromalidae), A Gregarious Parasitoid of Megachile Rotundata(Hymenoptera: Megachilidae)

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