Detection and characterization of bacterial endosymbionts inSoutheast Asian tephritid fruit fly populations

Abstract

BackgroundVarious endosymbiotic bacteria, including Wolbachia of the Alphaproteobacteria, infect a wide range ofinsects and are capable of inducing reproductive abnormalities to their hostssuch as cytoplasmic incompatibility (CI), parthenogenesis, feminization andmale-killing. These extended phenotypes can be potentially exploited inenhancing environmentally friendly methods, such as the sterile insect technique(SIT), for controlling natural populations of agricultural pests. The goal ofthe present study is to investigate the presence of Wolbachia, Spiroplasma,Arsenophonus and Cardinium among Bactrocera,Dacus and Zeugodacus flies of Southeast Asian populations, and to genotypeany detected Wolbachia strains.ResultsA specific 16S rRNA PCR assay wasused to investigate the presence of reproductive parasites in naturalpopulations of nine different tephritid species originating from three Asiancountries, Bangladesh, China and India. Wolbachia infections were identified in Bactrocera dorsalis, B.correcta, B. scutellaris andB. zonata, with 12.2–42.9% occurrence,Entomoplasmatales in B. dorsalis, B. correcta, B.scutellaris, B. zonata,Zeugodacus cucurbitae and Z. tau (0.8–14.3%) and Cardinium in B. dorsalis andZ. tau (0.9–5.8%), while none of thespecies tested, harbored infections with Arsenophonus. Infected populations showed a medium (between 10and 90%) or low (< 10%) prevalence, ranging from 3 to 80% for Wolbachia, 2 to 33% for Entomoplasmatales and 5 to45% for Cardinium. Wolbachia and Entomoplasmatales infections were found both intropical and subtropical populations, the former mostly in India and the latterin various regions of India and Bangladesh. Cardinium infections were identified in both countries but onlyin subtropical populations. Phylogenetic analysis revealed the presence ofWolbachia with some strains belongingeither to supergroup B or supergroup A. Sequence analysis revealed deletions ofvariable length and nucleotide variation in three Wolbachia genes. Spiroplasmastrains were characterized as citri–chrysopicola–mirum and ixodetis strainswhile the remaining Entomoplasmatales to the Mycoides–Entomoplasmataceae clade.Cardinium strains were characterized asgroup A, similar to strains infecting Encarsiapergandiella.ConclusionsOur results indicated that in the Southeast natural populationsexamined, supergroup A Wolbachia straininfections were the most common, followed by Entomoplasmatales and Cardinium. In terms of diversity, most strains ofeach bacterial genus detected clustered in a common group. Interestingly, thedeletions detected in three Wolbachia geneswere either new or similar to those of previously identified pseudogenes thatwere integrated in the host genome indicating putative horizontal gene transferevents in B. dorsalis, B. correcta and B.zonata.