Figure 2

The egg surface sterilization treatment reduced the bacterial microbiota of the I. ricinus larvae. The labels ‘Water’ and ‘Bleach’ (on the X-axis) refer to the control and surface sterilization treatments that were applied to the eggs that had been laid by the 10 engorged adult female I. ricinus ticks. For each of the 20 batches of larvae (10 tick families × 2 egg surface treatments), we froze subsets of  ~ 200 larvae at 6 weeks after hatching and extracted the DNA in pools of ~ 100 larvae (total of 40 pools). We used qPCR to determine the ratio of the bacterial 16S rRNA gene copy number to the tick calreticulin gene copy number, which measures the abundance of the tick-associated bacterial microbiota. This ratio was 28 times higher for the control larvae that hatched from the control eggs (‘Water’ treatment) compared to the dysbiosed larvae that hatched from the surface-sterilized eggs (‘Bleach’ treatment), and this difference was highly significant (p = 0.0000005). The ratios of the bacterial 16S rRNA to tick calreticulin gene copy numbers were log10-transformed to improve normality and the appearance of the graph. The boxplots show the median (black line), 25th and 75th percentiles (edges of the box), and minimum and maximum values (whiskers).