Extended starvation reduced and eliminated Wolbachia, but not Cardinium, from Metaseiulus occidentalis females (Acari: Phytoseiidae): a need to reassess Wolbachia's status in this predatory mite?

The presence of Wolbachia and Cardinium bacteria has been documented in many arthropod species, including the predatory mite Metaseiulus (=Typhlodromus or Galendomus) occidentalis (Nesbitt) (Acari: Phytoseiidae). We show that Tetranychus urticae, the prey of Metaseiulus occidentalis, contains Wolbachia and no detectable Cardinium using quantitative PCR (qPCR). Starvation for 72 h at 22°C eliminated most, if not all, Wolbachia in M. occidentalis adult females from 7 laboratory colonies. Refeeding of M. occidentalis with T. urticae after starvation for 72 h restored the amounts of Wolbachia in M. occidentalis to those of prestarvation levels, suggesting that Wolbachia detected in M. occidentalis starved for shorter periods of time in current, and some previous, studies likely came from T. urticae. Furthermore, eggs from all M. occidentalis colonies examined were free of Wolbachia if they were surface-decontaminated with 0.3% sodium hypochlorite before DNA extraction. Cardinium was present in 6 of 14 laboratory colonies of M. occidentalis. Starvation for 3, 24, 48, and 72 h had no effect on the amounts of Cardinium in adult females from the Cardinium-positive colonies. Eggs from these colonies were positive for Cardinium but contained less than 1% of the titers found in adult females. The data suggest that Cardinium, but not Wolbachia, is an endosymbiont in certain populations of M. occidentalis. In light of our current findings, we recommend specific practices for the identification of potential symbionts in predatory arthropod species using the PCR.