Complementary Sex Determination in the Parasitic Wasp Diachasmimorpha longicaudata

Abstract

We studied the sex determination in Diachasmimorpha longicaudata, a parasitoid braconid wasp widely used as biological control agent of fruit pest tephritid flies. We tested the complementary sex determination hypothesis (CSD) known in at least 60 species of Hymenoptera. According to CSD, male or female development depends on the allelic composition of one sex locus (single-locus CSD) or multiple sex loci (multiple-locus CSD). Hemizygote individuals are normal haploid males, and heterozygotes for at least one sex locus are normal diploid females, but homozygotes for all the sex loci are diploid males. In order to force the occurrence of diploid males in D. longicaudata, we established highly inbred lines and examined their offspring using chromosome counting, flow cytometry, and sex ratio analysis. We found that when mother-son crosses were studied, this wasp produced about 20% of diploid males out of the total male progeny. Our results suggest that this parasitoid may represent the second genus with multiple-locus CSD in Hymenoptera. Knowledge about the sex determination system in D. longicaudata is relevant for the improvement of mass rearing protocols of this species. This information also provides the necessary background for further investigations on the underlying molecular mechanisms of sex determination in this species, and a better insight into the evolution of this pathway in Hymenoptera in particular and insects in general.

Spermatogenesis in the parasitoid Diachasmimorpha longicaudata (Hymenoptera: Braconidae)

“…The size of the nuclei of their spermatocytes is significantly larger compared to that of haploid males, and they are also capable of producing mature spermatozoa (Carabajal Paladino et al . ). Diploid males have been described in at least 83 hymenopteran species (Harpur et al .…”

“…The similarities observed between D. longicaudata and H. juglandis , together with the observations made by Carabajal Paladino et al . () permit to infer that D. longicaudata diploid males may produce diploid gametes as well. This should certainly be investigated in the future.…”

Parthenogenesis in Hexapoda: holometabolous insects

“…Up to now, diploid males have been described in several dozen species of the Hymenoptera (Harpur, Sobhani, & Zayed, ). These males are often sterile, but fully functional and fertile ones were also found in a few hymenopteran species (Cowan & Stahlhut, ; Krieger, Ross, Chang, & Keller, ), thus showing that sex determination in this order is more complex than previously thought (Carabajal Paladino et al., ). Crosses of diploid females with these males can therefore produce triploid females (Krieger et al., ).…”

Transcriptome profiling of Diachasmimorpha longicaudata towards useful molecular tools for population management

“…Many studies performed on biological parameters [ 6 ], conditions of rearing [ 7 ], and behavior [ 4 , 8 , 9 ] are available for this parasitoid. Inbreeding experiments provided the first description of viable diploid males in this species, and the presence of a multiple-locus CSD mechanism [ 10 , 11 ] based on cytogenetic and cytological techniques and sex ratio analysis [ 12 ]. A deeper knowledge of D. longicaudata genomics is needed for a better understanding of the molecular basis of complex mechanisms, as the sex determination pathway.…”