Bacterial associates of seed-parasitic wasps (Hymenoptera: Megastigmus)

Abstract

BackgroundThe success of herbivorous insects has been shaped largely by their association with microbes. Seed parasitism is an insect feeding strategy involving intimate contact and manipulation of a plant host. Little is known about the microbial associates of seed-parasitic insects. We characterized the bacterial symbionts of Megastigmus (Hymenoptera: Torymidae), a lineage of seed-parasitic chalcid wasps, with the goal of identifying microbes that might play an important role in aiding development within seeds, including supplementing insect nutrition or manipulating host trees. We screened multiple populations of seven species for common facultative inherited symbionts. We also performed culture independent surveys of larvae, pupae, and adults of M. spermotrophus using 454 pyrosequencing. This major pest of Douglas-fir is the best-studied Megastigmus, and was previously shown to manipulate its tree host into redirecting resources towards unfertilized ovules. Douglas-fir ovules and the parasitoid Eurytoma sp. were also surveyed using pyrosequencing to help elucidate possible transmission mechanisms of the microbial associates of M. spermotrophus.ResultsThree wasp species harboured Rickettsia; two of these also harboured Wolbachia. Males and females were infected at similar frequencies, suggesting that these bacteria do not distort sex ratios. The M. spermotrophus microbiome is dominated by five bacterial OTUs, including lineages commonly found in other insect microbiomes and in environmental samples. The bacterial community associated with M. spermotrophus remained constant throughout wasp development and was dominated by a single OTU – a strain of Ralstonia, in the Betaproteobacteria, comprising over 55% of all bacterial OTUs from Megastigmus samples. This strain was also present in unparasitized ovules.ConclusionsThis is the first report of Ralstonia being an abundant and potentially important member of an insect microbiome, although other closely-related Betaproteobacteria, such as Burkholderia, are important insect symbionts. We speculate that Ralstonia might play a role in nutrient recycling, perhaps by redirecting nitrogen. The developing wasp larva feeds on megagametophyte tissue, which contains the seed storage reserves and is especially rich in nitrogen. Future studies using Ralstonia-specific markers will determine its distribution in other Megastigmus species, its mode of transmission, and its role in wasp nutrition.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-014-0224-4) contains supplementary material, which is available to authorized users.

Influence of host phylogeny, geographical location and seed harvesting diet on the bacterial community of globally distributed Pheidole ants

“…The second most prevalent was the genus Acinetobacter, with 20% relative frequency, which was already documented as common in arthropod microbiota (Esposti & Romero, 2017), in Solenopsis ant species (Ishak et al, 2011), in Nasonia (Brucker & Bordenstein, 2012), wasps (Paulson, Von Aderkas & Perlman, 2014) and present in the microbiota of Atta fungus-growing ants (Meirelles et al, 2016).…”

“…In Carabid beetles (which consume insect prey as well as seeds), these bacteria were found associated with dietary treatment of seeds (Lundgren & Lehman, 2010). In a study to determine the bacterial symbionts associated with the seed-parasitic insect Megastigmus (Hymenoptera: Torymidae) Paulson, Von Aderkas & Perlman (2014) also found Ralstonia as the dominant bacteria genus. In a subsequent study of Megastigmus with transcriptome analysis, many mobile genetic elements transcripts from Ralstonia were discovered (Paulson et al, 2016), corroborating the association of this bacterial genus with Megastigmus.…”

Transcriptome analysis provides insight into venom evolution in a seed‐parasitic wasp, Megastigmus spermotrophus

“…Nearly half (47.3%) of nonredundant annotations assigned to the M. spermotrophus transcriptome were from the model parasitoid and close relative N. vitripennis and 77.3% of all nonredundant annotations were of insect origin. Interestingly, many transcripts (10.6% of nonredundant annotations) were assigned from the bacterial genus Ralstonia (Betaproteobacteria), which corroborated the recent findings that this bacterium is pervasively associated with different life stages of M. spermotrophus (Paulson et al ., ). Interestingly, the four most highly expressed Ralstonia ‐attributed contigs are related to mobile genetic elements, including transposase IS66 (YP_001899056.1), ISPsy11 transposase OrfB (ZP_10987507.1), resolvase domain protein (ZP_10982688.1) and putative cointegrate resolution protein T (ZP_07678195.1).…”

Metagenomic analysis of microbial community of a parasitoid wasp Megaphragma amalphitanum

“…1). Nevertheless, its composition differs from much bigger parasitoid wasps - Nasonia , Asobara , Megastigmus [9], [10], [11]. Moreover, microbiota samples of M. amalphitanum from Northern Italy do not have representatives of Rickettsia and Wolbachia genus.…”