The endosymbiotic bacterium Wolbachia reduces longevity but seems essential for ongoing culture of the parasitoid wasp, Diadegma semiclausum, a commercially important biocontrol agent.

AIMS: Diadegma semiclausum is an important parasitoid wasp and biological control agent of diamondback moth, Plutella xylostella. Diadegma semiclausum is naturally infected with the endosymbiotic bacterium Wolbachia. In other hymenopterans, Wolbachia can influence host reproduction and fitness, but its effects in D. semiclausum are unknown.

METHODS AND RESULTS: Preliminary experiments suggested Wolbachia could not be cured from D. semiclausum with antibiotics, and multi-generational exposure to antibiotics ultimately crashed lines. This led us to infer that Wolbachia is essential for reproduction. We then examined phenotypic effects following partial suppression of Wolbachia using six antibiotic concentrations (0, 0.06, 0.6, 6, and 60 mg ml⁻¹ tetracycline and rifampicin) and a non-injected control. In the exposed G0 generation, control wasps exhibited negative associations between longevity and Wolbachia density, suggesting that high Wolbachia densities reduced life span. Antibiotic-treated G0 wasps exhibited reduced Wolbachia densities but did not exhibit associations between Wolbachia density and longevity. In the next G1 generation, Wolbachia densities generally recovered across treated groups and converged on longevity patterns seen in the control group.

CONCLUSION: We highlight the resilience of the Wolbachia infection in D. semiclausum wasps but also its potential costs at a high density. Future work could explore whether artificial selection could produce strains that exhibit better performance under mass-rearing conditions.