Arsenophonus nasoniae and Rickettsiae Infection of Ixodes ricinus Due to Parasitic Wasp Ixodiphagus hookeri

Abstract Arsenophonus nasoniae, a male-killing endosymbiont of chalcid wasps, was recently detected in several hard tick species. Following the hypothesis that its presence in ticks may not be linked to the direct occurrence of bacteria in tick's organs, we identified A. nasoniae in wasps emerging from parasitised nymphs. We confirmed that 28.1% of Ixodiphagus hookeri wasps parasitizing Ixodes ricinus ticks were infected by A. nasoniae. Moreover, in examined I. ricinus nymphs, A. nasoniae was detected only in those, which were parasitized by the wasp. However, in part of the adult wasps as well as in some ticks that contained wasp's DNA, we did not confirm A. nasoniae. We also found, that in spite of reported malekilling, some newly emerged adult wasp males were also infected by A. nasoniae. Additionally, we amplified the DNA of Rickettsia helvetica and Rickettsia monacensis (known to be Ixodes ricinus-associated bacteria) in adult parasitoid wasps. This may be related either with the digested bacterial DNA in wasp body lumen or with a role of wasps in circulation of rickettsiae among tick vectors

Arsenophonus nasoniae and Rickettsiae Infection of Ixodes ricinus Due to Parasitic Wasp Ixodiphagus hookeri

International audienceArsenophonus nasoniae, a male-killing endosymbiont of chalcid wasps, was recently detected in several hard tick species. Following the hypothesis that its presence in ticks may not be linked to the direct occurrence of bacteria in tick's organs, we identified A. nasoniae in wasps emerging from parasitised nymphs. We confirmed that 28.1% of Ixodiphagus hookeri wasps parasitizing Ixodes ricinus ticks were infected by A. nasoniae. Moreover, in examined I. ricinus nymphs, A. nasoniae was detected only in those, which were parasitized by the wasp. However, in part of the adult wasps as well as in some ticks that contained wasp's DNA, we did not confirm A. nasoniae. We also found, that in spite of reported male-killing, some newly emerged adult wasp males were also infected by A. nasoniae. Additionally, we amplified the DNA of Rickettsia helvetica and Rickettsia monacensis (known to be Ixodes ricinus-associated bacteria) in adult parasitoid wasps. This may be related either with the digested bacterial DNA in wasp body lumen or with a role of wasps in circulation of rickettsiae among tick vectors

The questionable role of parasitic wasps in the transmission of rickettsiae, illustrated on the tick’s life cycle.

<p>Adult female <i>I</i>. <i>hookeri</i> oviposits in larvae and nymphs of ixodid ticks, but the wasp eggs start to develop only in fully engorged nymphs. The immature parasitoid wasps consume the nymph’s tissue and its ingested blood meal, causing nymph death. During the tick’s life cycle (eggs, larvae, nymphs, adults), rickettsiae can pass from stage to stage. In our experiments we successfully amplified rickettsial DNA not just in unfed nymphs but also in emerged adult wasps. More experiments will be needed to demonstrate if <i>I</i>. <i>hookeri</i> may act as a biological vector of <i>A</i>. <i>nasoniae</i> and <i>Rickettsia</i> sp.</p

<i>Ixodiphagus hookeri</i> adults.

<p>(A) Habitus of a female after treatment with <i>Marc André</i> solution. (B) Magnified female genitalia. (C) Habitus of a male. (D) Magnified male genitalia. Scale bar represents 0.5 mm.</p

Reports on <i>Ixodiphagus hookeri</i> detected in hard ticks.

<p>Reports on <i>Ixodiphagus hookeri</i> detected in hard ticks.</p

Detection of bacteria and wasps in unfed <i>I</i>. <i>ricinus</i> nymphs.

<p>Overall 41 host-seeking <i>I</i>. <i>ricinus</i> nymphs were examined for the presence of <i>A</i>. <i>nasoniae</i> and <i>Rickettsia</i> sp. as well as for <i>I</i>. <i>hookeri</i> by PCR. The DNA of <i>A</i>. <i>nasoniae</i> was successfully amplified in 4 nymphs (9.8%) and the presence of rickettsiae was confirmed in 5 nymphs (12.2%). Six nymphs were parasitized by <i>I</i>. <i>hookeri</i> wasps (14.6%). As shown in the Venn-diagram, all nymphs that were positive for <i>A</i>. <i>nasoniae</i> were simultaneously parasitized by <i>I</i>. <i>hookeri</i>. Co-infection by both bacteria occurred only in one <i>I</i>. <i>ricinus</i> nymph which also contained wasp DNA.</p

Published studies on detection of <i>Arsenophonus nasoniae</i> in ticks.

<p>Published studies on detection of <i>Arsenophonus nasoniae</i> in ticks.</p

Workflow of laboratory experiments.

<p>A total of 360 <i>I</i>. <i>ricinus</i> nymphs were fed on 12 Balb/c mice. Of those, 50 engorged nymphs were parasitized by <i>I</i>. <i>hookeri</i> wasps. The obtained 96 parasitoids were subsequently screened for the presence of <i>A</i>. <i>nasoniae</i> and rickettsiae by PCR. The DNA of <i>A</i>. <i>nasoniae</i> was found in 27 wasps (28.1%), <i>Rickettsia</i> sp. in 22 wasps (22.9%). Eight wasps were positive for both bacteria—<i>A</i>. <i>nasoniae</i> and <i>Rickettsia</i> sp.</p