ISSN:
1570-7458
Keywords:
Pteromalidae
;
Dinarmus vagabundus
;
Bruchidae
;
Callosobruchus maculatus
;
Ectoparasite grégaire
;
Rapport des sexes
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Description / Table of Contents:
Summary The effect of the density of ♀ parasitoids upon their hosts (Callosobruchus maculatus) was studied by the sex-ratio of the offspring of one, two or three ♀ parasitoids, each put in an experimental box. Each group of females received daily four seeds of Vigna radiata infested by the host; each seed contained on average two host larvae of 18–20 days old. After 24 hours with the parasites, the 4 seeds were removed to separate containers so the parasites emerging from each could be examined. The number of larvae/host increases when two or three ♀ parasitoids (D. vagabundus) attack the same host. The average number of offspring (daughters and sons) during the first 20 days of the reproductive activity rises significantly with the number of ovipositing ♀♀. When the density of ovipositing ♀♀ is increased from one to three, the sex-ratio of the offspring ♂/♀ changes towads the value one, with the proportion of emergent sons increasing more quickly than that of the daughters. The increase of the parasitoid numbers in one host causes a modification of the sexratio, favouring ♂ ♂. In our experimental conditions we find 1) significant increase in emergent daughters in the presence of three ovipositing ♀♀, 2) elevation in number of emergent sons as soon as there is more than one ovipositing ♀. In the presence of only one ovipositing ♀, an average of one ♂ emerges per host, this average production of 0.5 increases in the presence of two ovipositing ♀♀ and is doubled in the presence of three ♀.
Notes:
Abstract Lorsque 2 femelles ou 3 femelles de l'ectoparasite D. vagabundus parasitent conjointement un même lot d'hôtes l'intensité du grégarisme larvaire s'accroît par rapport à celui observé en présence d'une seule femelle pondeuse. Cela se traduit par une augmentation significative du nombre moyen de descendants des 2 sexes mais la production moyenne en fils est toujours très inférieure à celle des filles. Cependant, lorsque la densité de femelles pondeuses passe de 1 à 3, le rapport des sexes mâles/femelles des descendants évolue vers l'unité traduisant une augmentation plus rapide de l'effectif des fils que des filles.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00186932
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