Abstract
The cabbage root fly Delia radicum is a worldwide pest that causes yield losses of many common cabbage crops. The bacteria associated with D. radicum are suggested to influence the pest status of their host. In this study, we characterized insect-associated bacteria of D. radicum across multiple life stages and of their diet plant (turnip, Brassica rapa subsp. rapa) by sequencing the V3–V4 region of 16S rRNA genes using the Illumina MiSeq platform. In total, over 1.2M paired-end reads were obtained, identifying 1006 bacterial amplicon sequence variants (ASVs) in samples obtained from the eggs, larvae, pupae and adults of D. radicum, as well as turnips that were either fresh or infested with D. radicum larvae. The microbial community in D. radicum was dominated by Wolbachia, a common endosymbiont of arthropods which we found in all of the investigated insect samples, with the pupal stage having the highest relative abundance. Moderate amounts of Firmicutes were found only in adult D. radicum flies, but not in previous life stages. Actinobacteria were mostly found on the eggs and on the skin of fresh plants on which the eggs were deposited. These plants also harbored a large amount of Pseudomonas. The bacterial diversity of the healthy turnip was low, whereas the microbial community of decaying turnips that were heavily infested by D. radicum larvae and showing symptoms of advanced soft rot was characterized by a high bacterial diversity. Taken together, this work provides insights into the bacterial communities associated with the cabbage pest D. radicum and its associated disease symptoms.
Highlights
Studies that characterize the microbial community profiles of different insect species are gaining increasing attention, yet not much is known about the microbiome of the cabbage root fly Delia radicum
We identified the major differences of bacterial communities that were associated with healthy the feed plants Brassica rapa subsp. rapa pre-predation, compared to plants that were macerated after being invaded by D. radicum larvae
Bacterial species richness in the microbiome of D. radicum is highest in the larval stage, most likely due to the presence of a gut that is filled with decaying plant matter that is, as we show here, characterized by a highly complex bacterial community
Summary
Studies that characterize the microbial community profiles of different insect species are gaining increasing attention, yet not much is known about the microbiome of the cabbage root fly Delia radicum. This crop pest can cause devastating yield losses on many popular vegetable crops, e.g., cabbage, kohlrabi or rapeseed (Soroka et al, 2004; Dosdall et al, 2012). The females of this species deposit their eggs onto or near the stem of cruciferous plants and emerging larvae bore into root tissue. This study showed that certain gut symbionts of P. xylostella can have significant impact on fitness, the intestinal tracts of caterpillars are typically characterized by short transit times and a high pH which make microbial colonization difficult, and wild Lepidoptera (caterpillars) have been suggested to typically lack resident gut symbionts (Hammer et al, 2017)
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