Abstract
Background
Various endosymbiotic bacteria, including Wolbachia of 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 of Wolbachia, Spiroplasma,Arsenophonus and Cardinium among Bactrocera,Dacus and Zeugodacus flies of Southeast Asian populations, and to genotype
any detected Wolbachia strains.
Results
A specific 16S rRNA PCR 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. 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 the
species tested, harbored infections with Arsenophonus. Infected populations showed a medium (between 10
and 90%) or low (< 10%) prevalence, ranging from 3 to 80% for Wolbachia, 2 to 33% for Entomoplasmatales and 5 to
45% for Cardinium. Wolbachia and 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. Cardinium infections were identified in both countries but only
in subtropical populations. Phylogenetic analysis revealed the presence ofWolbachia with some strains belonging
either to supergroup B or supergroup A. Sequence analysis revealed deletions of
variable length and nucleotide variation in three Wolbachia genes. Spiroplasma
strains were characterized as citri–chrysopicola–mirum and ixodetis strains
while the remaining Entomoplasmatales to the Mycoides–Entomoplasmataceae clade.Cardinium strains were characterized as
group A, similar to strains infecting Encarsia
pergandiella.
Conclusions
Our results indicated that in the Southeast natural populations
examined, supergroup A Wolbachia strain
infections were the most common, followed by Entomoplasmatales and Cardinium. In terms of diversity, most strains of
each bacterial genus detected clustered in a common group. Interestingly, the
deletions detected in three Wolbachia genes
were either new or similar to those of previously identified pseudogenes that
were integrated in the host genome indicating putative horizontal gene transfer
events in B. dorsalis, B. correcta and B.
zonata.
Comparative genomic and transcriptomic analyses of chemosensory genes in the citrus fruit fly Bactrocera (Tetradacus) minax
