Absence of complementary sex determination in two Leptopilina species(Figitidae,Hymenoptera)and a reconsideration of its incompatibility with endosymbiont-induced thelytoky

Complementary sex determination(CSD)is a widespread sex determination mechanism in haplodiploid Hymenoptera.Under CSD,sex is determined by the allelic state of one or multiple CSD loci.Heterozygosity at one or more loci leads to female development,whereas hemizygosity of haploid eggs and homozygosity of diploid eggs results in male development.Sexual(arrhenotokous)reproduction normally yields haploid male and diploid female offspring.Under asexual reproduction(thelytoky),diploidized unfertilized eggs develop into females.Thelytoky is often induced by bacterial endosymbionts that achieve egg diploidization by gamete duplication.As gamete duplication leads to complete homozygosity,endosymbiont-induced thelytokous reproduction is presumed to be incompatible with CSD,which relies on heterozygosity for female development.Previously,we excluded CSD in four Asobara(Braconidae)species and proposed a two-step mechanism for Wolbachia-induced thelytoky in Asobara japonica.Here,we conclusively reject CSD in two cynipid wasp species,Leptopilina heterotoma and Leptopilina clavipes.We further show that thelytoky in L.clavipes depends on Wolbachia titer but that diploidization and feminization steps cannot be separated,unlike in A.japonica.We discuss what these results reveal about the sex determination mechanism of L.clavipes and the presumed incompatibility between CSD and endosymbiont-induced thelytoky in the Hymenoptera.

Thelytokous Diglyphus wani:A more promising biological control agent against agromyzid leafminers than its arrhenotokous counterpart

Diglyphus wani(Hymenoptera:Eulophidae)is a dominant parasitoid that attacks agromyzid leafminers.Two reproductive types occur in D.wani:arrhenotoky(in which virgin females produce only male offspring;and virgin females mate with males to produce bisexual offspring)and thelytoky(in which virgin females produce female offspring).As a potential biological control agent,exploring the differences in the relevant biological parameters of both strains is necessary.In this study,comparisons between the two strains of D.wani were performed by evaluating the life table and host-killing rate.The thelytokous strain exhibited significantly better life table parameters than its arrhenotokous counterpart.Higher values for the intrinsic rate of increase,finite rate of increase,net reproductive rate,and fecundity were found in the thelytokous strain.The thelytokous strain also performed better than the arrhenotokous strain in terms of net parasitism,host-feeding,host-stinging,and total host-killing rates.Thus,populations of the thelytokous strain could grow fast and kill more hosts.In conclusion,the thelytokous strain of D.wani may be the more promising biological agent against agromyzid leafminers compared to its arrhenotokous counterpart.Also,since the thelytokous strain of D.wani is only known to produce females,it should be given priority in future biocontrol applications owing to the cost savings of breeding only females.

First molecular genetic evidenee for automictic parthenogenesis in cockroaches

Parthenogenesis is an asexual mode of reproduction that plays an important role in the evolution of sex, sociality, and reproduction strategies in insects. Some species of cockroach exhibit thelytoky, a type of parthenogenesis in which female offspring are produced without fertilization. However, the cytological and genetic mecha? nisms of parthenogenesis in cockroaches are not well understood. Here we provide the first molecular genetic evidence that cockroaches can reproduce through automixis. Using the American cockroach Periplaneta aniericana, we performed microsatellite analysis to investigate the genetic relationship between parthenogenetically produced nymphs and the parent virgin females, and found that all parthenogenetic offspring were homozygous for autosomal microsatellite markers, whereas the female parents were heterozygous. In addition, flow cytometry analysis revealed that the parthenogenetic offspring were diploid. Taken together, our results demonstrate that P. americana exhibits automixis-type thelytoky, in which diploidy is restored by gamete duplication or terminal fusion. These findings highlight the unique reproduction strategies of cockroaches, which are more varied than was previously recognized.