Use of tetracycline in larval diet to study the effect of Wolbachia on host fecundity and clarify taxonomic status of Trichogramma species in cured bisexual lines

Endosymbionts of the genus Wolbachia were efficiently cured from Trichogramma species by incorporating 0.02% tetracycline into the artificial diet used to rear larvae. Use of this technique yielded stable cured lines (bisexual and arrhenotokous lines) in which no Wolbachia organisms were detected by PCR for up to 14 generations after curing. Four cured strains of Trichogramma pretiosum showed a significantly lower total fecundity compared to their Wolbachia-infected counterpart. However, the fecundity of a single cured strain of Trichogramma evanescens was similar to its Wolbachia-infected counterpart. These differences in the effect on fecundity may be due to differences between the Wolbachia strains infecting T. pretiosum or T. evanescens, providing additional evidence for the hypothesis that a specific interaction exists between some Trichogramma species and their Wolbachia symbionts. Tetracycline in larval diet was also used to generate bisexual strains of Trichogramma oleae and Trichogramma cordubensis so that these species could be crossed with the closely related species, respectively, T. pretiosum and T. evanescens, to test their compatibility. These crosses showed a lack of compatibility, validating maintenance of these as distinct species.