Wolbachia in scale insects: a distinct pattern of infection frequencies and potential transfer routes via ant associates

Abstract

Wolbachia is one of the most successful endosymbiotic bacteria of arthropods. Known as the 'master of manipulation', Wolbachia can induce a wide range of phenotypes in its host that can have farreaching ecological and evolutionary consequences and may be exploited for disease and pest control. However, our knowledge of Wolbachia's distribution and the infection rate is unevenly distributed across arthropod groups such as scale insects. We fitted a distribution of within-species prevalence of Wolbachia to our data and compared it to distributions fitted to an up-to-date dataset compiled from surveys across all arthropods. The estimated distribution parameters indicate a Wolbachia infection frequency of 43.6% (at a 10% prevalence threshold) in scale insects. Prevalence of Wolbachia in scale insects follows a distribution similar to exponential decline (most species are predicted to have low prevalence infections), in contrast to the U-shaped distribution estimated for other taxa (most species have a very low or very high prevalence). We observed no significant associations between Wolbachia infection and scale insect traits. Finally, we screened for Wolbachia in scale insect's ecological associates. We found a positive correlation between Wolbachia infection in scale insects and their ant associates, pointing to a possible route of horizontal transfer of Wolbachia.

Host phylogeny and ecological associations best explain Wolbachia host shifts in scale insects

“…In a previous study, a positive correlation between Wolbachia infection in scale insects and their associates indicated that ants may play a role in host‐shifting (Sanaei, Lin, et al, 2021). Here, we found that only one out of five cases of infected ant–scale insect pairs shares the same Wolbachia strain (Table S2, Figure S4).…”

“…In a previous study, we screened 689 scale insect specimens for Wolbachia (Sanaei, Lin, et al, 2021). Among samples with positive Wolbachia infection, we selected those whose multilocus sequence typing (MLST) genes (Baldo et al, 2006) were successfully amplified.…”

“…In particular, many are usually observed in close interactions with ants through trophallaxis (where the honeydew produced by the scale insects is consumed by ants) (Buckley & Gullan, 1991; Gullan et al, 1993; Hölldobler et al, 1990). Despite several similarities with other hemipterans, Sanaei, Lin, et al (2021) found that most species are predicted to have low to intermediate Wolbachia prevalence, in contrast to a u‐shaped distribution (most species have a very low or very high prevalence) predicted for other groups (Hilgenboecker et al, 2008). Also, a positive correlation between Wolbachia infection in scale insects and their associate ants indirectly points to a plausible route of transfer (Sanaei, Lin, et al, 2021).…”

“…Despite several similarities with other hemipterans, Sanaei, Lin, et al (2021) found that most species are predicted to have low to intermediate Wolbachia prevalence, in contrast to a u‐shaped distribution (most species have a very low or very high prevalence) predicted for other groups (Hilgenboecker et al, 2008). Also, a positive correlation between Wolbachia infection in scale insects and their associate ants indirectly points to a plausible route of transfer (Sanaei, Lin, et al, 2021). These preliminary results provided a broad view of the Wolbachia infection dynamics in scale insects and thus inspired us to investigate Wolbachia strain diversity and consequently host‐shifting in scale insects.…”

Mutualism enhances Wolbachia infection rates in ant-attended Tuberculatus aphid species (Hemiptera: Aphididae)

“…Thus, the horizontal transmission of endosymbionts via the parasitoids of insects represents a potential pathway. Besides parasitoid wasps, ants are also known to harbour Wolbachia (Keller et In the study of scale insects and their associated groups (ants, wasps, beetles, ies, mites, moths, and thrips), Sanaei et al (2021) showed that signi cant differences in Wolbachia infection rates in the scale insects were found in ant attendance and the associated groups but wasps, suggesting a possible route of horizontal transfer between ants and scale insects. Nonetheless, it is unlikely that Wolbachia was transported by ants into Tuberculatus aphids because the two nonattended species, T. higuchii A-and B-types, showed over 10% infection rates and a mean infection rate of 30% in ant-attended species seems to be a low score considering constant contact with ants.…”