453 INTRODUCTION Wolbachia is a genus of maternally inherited intracellu- lar α-proteobacteria which infect a wide range of arthro- pods and nematodes (Werren, 1997; Braig et al., 1998; Stouthamer et al., 1999), estimated to occur in about 66% of all known insect species (Hilgenboecker et al., 2008). They are abundant intracellular symbionts and have at- tracted signifcant attention in terms of their ability to ma- nipulate host reproduction through cytoplasmic incompat- ibility (CI), feminization, induction of parthenogenesis and male killing (Werren, 1997; Stouthamer et al., 1999). In CI, infected males are incompatible with uninfected females or females infected with some other strains of Wolbachia; however, infected females are compatible with infected or uninfected males (Yen & Bar, 1971; O’Neill & Karr, 1990). This is the most commonly observed Wolbachia- induced reproductive phenotype in most of insect orders. Feminization is the reproductive phenotype whereby all genetic males are converted into functional females, and is found in some terrestrial isopods as well as one particular species of butterfy (Rigaud et al., 1991; Kageyama et al., 2002). However, in other lepidopteran species such as the corn borer, Ostrinia scapulalis (Crambidae), Wolbachia causes lethal feminization of genotypic males (Kageyama & Traut, 2004; Sugimoto & Ishikawa, 2012). During par- thenogenesis, unfertilized eggs develop into males (arrehe- notoky) or females (thelytoky) (Werren et al., 2008). Each of these reproductive anomalies enhances female produc- tion and hence the reproduction of the bacterium and is col- lectively referred to as “reproductive parasitism” (Werren et al., 2008). The effect of Wolbachia depends on a number of factors, including host genetic background, atmospheric tempera- ture, resource quality and host age. These factors directly affect Wolbachia densities within its host, which in turn have context specifc effects on the respective host popu- lations. Among these, temperature has a remarkable ef- fect upon Wolbachia, associated bacteriophage, involved in horizontal gene transfer (Bordenstein & Wernegreen, 2004) and on host population dynamics (Bordenstein & Werren, 2003; Bordenstein & Bordenstein, 2011; Kraaije- veld et al., 2011). Nesolynx thymus (Hymenoptera: Eulophidae) is an ecto- pupal-gregarious parasitoid of the “uzify”, Exorista sorb- illans (Diptera: Tachinidae), itself an endo-larval parasi- toid of the silkworm moth, Bombyx mori L. (Lepidoptera: Bombycidae), and accounting for some 8–10% yield loss in India and other silk growing countries. N. thymus is of- ten used as a primary biocontrol agent to regulate the popu- lations in nature (Narayanaswamy & Devaiah, 1998). Ear- lier investigations have associated the effcacy of this agent with its phenomenal host searching ability and parasitiza- tion capacity (Kumar et al., 1993; Narayanaswamy & De- vaiah, 1998). The successful expansion of the parasitoid is based on its ability to tolerate highly variable temperatures ranging from 15 to 35°C (Jyothi et al., 1993). The overall developmental time of the parasitoid from egg to adult is around 16 days, whilst gravid females can produce around 300 offspring during their lifetime. Interestingly, the sex ratio of the parasitoid has been found to vary considerably between studies (ChannaBasavanna et al., 1993; Aruna & Manjunath, 2010). In addition to its use as a biocon- trol agent against uzify, N. thymus also hyper-parasitizes Eur. J. Entomol. 111(4): 453–456, 2014 doi: 10.14411/eje.2014.059 ISSN 1210-5759 (print), 1802-8829 (online) Sex ratio distortion in the Nesolynx thymus (Hymenoptera: Eulophidae), an ecto-pupal parasitoid of uzify, Exorista sorbillans (Diptera: Tachinidae) Bandekodigenahalli M. PRAKASH  1 , aswathaiah PRATHIMA 2 , hoolageri C. HUCHESH  2 , hemagirigowda RAVIKUMAR 2 , shankaranarayan SAMPATHKUMAR 2 and hosagavi P. PUTTARAJU  2 1 Evolutionary Biology Laboratory, Evolutionary and Organismal Biology Unit, Jawaharlal Nehru Centre for Advanced Scientifc Research, Jakkur PO, Bangalore 560064, Karnataka, India; e-mail: prakashbm@gmail.com 2 Department of Biological Sciences, Bangalore University, Bangalore 560056, Karnataka, India; e-mails: prathima2805@gmail.com; hucheshbt@gmail.com; ravikumarh79@gmail.com; sam82kumar@gmail.com; puttarajuhp@hotmail.com Key words. Hymenoptera, Eulophidae, Diptera, Tachinidae, Wolbachia, Nesolynx thymus, Exorista sorbillans, sex ratio distortion, parthenogenesis, temperature treatment Abstract. The reproductive alterations induced by maternally inherited α-proteo-bacteria Wolbachia to their hosts is a well-document- ed phenomenon. In Nesolynx thymus, a gregarious hymenopterous ecto-pupal parasitoid of the uzify, Exorista sorbillans, diagnostic PCR assay using specifc primers revealed the presence of Wolbachia. Following genetic crossing experiments, we observed a female biased sex ratio of 1 : 9.5 at 25°C and 1 : 3 male to female ratio when the populations were exposed to heat shock 33°C for six hours. Furthermore, we found infection polymorphism, where female parasitoids are infected by Wolbachia but males are not infected. In- fected eggs develop into females, whereas uninfected eggs develop parthenogenetically into males. The results are discussed in the context of the possible mechanism of sex-ratio bias caused by Wolbachia.