A single parasitoid segregating factor controls immune suppression in Drosophila

Abstract

Encapsulation has evolved as an efficient mechanism whereby an insect host can survive infection by parasitoids This ability is controlled by a major gene in Drosophila melanogaster hosts. The parasitoid Leptopilina boulardi (Hymenoptera Eucoilidae) can suppress the Drosophila immune reaction by injecting viruslike particles. Analysis of Mendelian crosses between strains of L. boulardi of opposite immune suppressive abilities indicated that the trait is controlled by a single chromosomal factor with semidominant effect. We developed a method to test the monogenic hypothesis. The range of possible genotypic values in back-crosses was studied using various progeny that were genotypically homogenous. These could be obtained because of the arrhenotokous mode of reproduction. The progeny groups were divided into two clusters according to the major gene classification and the hypothesis of another unlinked genetic factor was rejected. Lastly, there was a residual progeny effect within the major groups, indicating that minor genes are also present. This study rules out the polygenic effect for a trait governing the interaction between the insect and parasitoid. It demonstrates that the genefor-gene model commonly found in plant-parasite interactions may also explain natural variations in insect-parasitoid traits.

Genetic dimension of the coevolution of virulence–resistance in Drosophila – parasitoid wasp relationships

“…The parasitoid reference strain (Gif stock no. 486) was obtained from an isofemale strain selected from a population collected in Brazzaville (Congo), as described in Dupas et al (1998). The level of encapsulation of the 940 reference host strain parasitised by the 486 reference strain was 97.3% (675 eggs tested).…”

Drosophila resistance genes to parasitoids: chromosomal location and linkage analysis

“…Its level of encapsulation was 97.3% (675 eggs tested) against L. boulardi and 100% (34 eggs tested) against A. tabida. Strain 249 has a Canton S strain origin and was demonstrated to be susceptible to A. tabida (Benassi et al 1998) The origins of the avirulent strains of L. boulardi (Gif stock number 486) and A. tabida (Gif stock number 490, Leiden stock WOV) are described elsewhere (Dupas et al 1998;Benassi et al 1998). Encapsulation occurs only in the case of parasitism of resistant D. melanogaster strains by the avirulent parasitoid strains.…”

Variability and genetic components of innate fruit odour recognition in a parasitoid of Drosophila

“…Indeed, 42% of the parasitic eggs are encapsulated due to the poor ability of Brazzaville females to suppress the immune defence of D. melanogaster. By contrast, it is fully suppressed by the strain originating from Nasrallah (Carton & Nappi, 1991;Dupas et al, 1998).…”

“…These strains have been used extensively to investigate the genetic basis of host±parasite immune interactions because they differ genetically in their ability to suppress the encapsulation of their egg by larvae of D. melanogaster (Dupas et al, 1998).…”

“…Kaiser & De Jong, 1995;Hedlund et al, 1996;Vet et al, 1998;Couty et al, 1999), and strains characterized by genetic differences in various traits are available (e.g. Carton et al, 1986;Fleury et al, 1995;Dupas et al, 1998), In Leptopilina sp., females locate their digging host larvae by repeated ovipositor insertions into the breeding substrate. This probing behaviour is triggered innately upon the perception of larval products and/or vibrations (Vet & Bakker, 1985;Vet & Van Alphen, 1985;Vet et al, 1993).…”