Detection and characterization of bacterial endosymbionts in Southeast Asian tephritid fruit fly populations

Abstract

AbstractBackgroundVarious endosymbiotic bacteria, includingWolbachiaof the Alphaproteobacteria, infect a wide range of insects and are capable of inducing reproductive abnormalities to their hosts such as cytoplasmic incompatibility (CI), parthenogenesis, feminization and male-killing. These extended phenotypes can be potentially exploited in enhancing environmentally friendly methods, such as the sterile insect technique (SIT), for controlling natural populations of agricultural pests. The goal of the present study is to investigate the presence ofWolbachia,Spiroplasma,ArsenophonusandCardiniumamongBactrocera,DacusandZeugodacusflies of Southeast Asian populations, and to genotype any detectedWolbachiastrains.ResultsA specific 16SrRNAPCR assay was used to investigate the presence of reproductive parasites in natural populations of nine different tephritid species originating from three Asian countries, Bangladesh, China and India.Wolbachiainfections were identified inBactrocera dorsalis,B. correcta,B. scutellarisandB. zonata, with 12.2–42.9% occurrence, Entomoplasmatales inB. dorsalis,B. correcta,B. scutellaris,B. zonata,Zeugodacus cucurbitaeandZ. tau(0.8–14.3%) andCardiniuminB. dorsalisandZ. tau(0.9–5.8%), while none of the species tested, harbored infections withArsenophonus. Infected populations showed a medium (between 10 and 90%) or low (< 10%) prevalence, ranging from 3 to 80% forWolbachia, 2 to 33% for Entomoplasmatales and 5 to 45% forCardinium.Wolbachiaand Entomoplasmatales infections were found both in tropical and subtropical populations, the former mostly in India and the latter in various regions of India and Bangladesh.Cardiniuminfections were identified in both countries but only in subtropical populations. Phylogenetic analysis revealed the presence ofWolbachiawith some strains belonging either to supergroup B or supergroup A. Sequence analysis revealed deletions of variable length and nucleotide variation in threeWolbachiagenes.Spiroplasmastrains were characterized as citri–chrysopicola–mirum and ixodetis strains while the remaining Entomoplasmatales to the Mycoides–Entomoplasmataceae clade.Cardiniumstrains were characterized as group A, similar to strains infectingEncarsia pergandiella.ConclusionsOur results indicated that in the Southeast natural populations examined, supergroup AWolbachiastrain infections were the most common, followed by Entomoplasmatales andCardinium. In terms of diversity, most strains of each bacterial genus detected clustered in a common group. Interestingly, the deletions detected in threeWolbachiagenes were either new or similar to those of previously identified pseudogenes that were integrated in the host genome indicating putative horizontal gene transfer events inB. dorsalis,B. correctaandB. zonata.