Prevalence of maternally-inherited bacteria in native and invasive populations of the harlequin ladybird beetle Harmonia axyridis

Harmonia axyridis Pallas (Coleoptera: Coccinellidae) has attracted a growing body of research trying to understand its invasion success in North America and Europe after being introduced from its original range central and east Asia. Its endosymbiotic microorganisms along with the introduction are often assumed to play a potential role in the invasion. We examined the prevalence of three common bacterial groups Rickettsia, Wolbachia and Spiroplasma in H. axyridis populations from 30 geographical locations across mainland China and nine across the Americas. Rickettsia was not detected in both native and non-native H. axyridis populations. Wolbachia infected only one native population at 9.5% but three non-native populations at rates from 3.6 to 25%. All Wolbalchia sequences were aligned to four haplotypes in two groups in the phylogenetic reconstruction. Spiroplasma was not found infecting non-native populations while it infected 15 native ones at rates from 1.6 to 20%. All Spiroplasma sequences were aligned to six haplotypes, among which five were new to H. axyridis populations from China and one was identical to that from Japan. All Spiroplasma lineages in native H. axyridis populations were representative of S. ixodetis. This geographic infection pattern across native and non-native H. axyridis populations suggests that these three groups of maternally-inherited bacteria may not be influential at the initial stages of invasion of H. axyridis in North America.