Figure 3

Dynamics of B. aphidicola population during aphid development.

(a,b) Variation in the number of symbiont cells, quantified by flow cytometry analysis from whole aphids (a), or embryonic chains (b), in relation to host developmental stage. Results are reported as means ± SD; n = 3 independent biological replicates per stage (each biological replicate was composed of 10 aphids). Data (after log-transformation) were analyzed by one-way ANOVA followed by a post hoc multiple comparisons test (Tukey’s HSD test). Developmental stages labeled with different letters are significantly different (P < 0.05). (c) Variation in the number of B. aphidicola cells in maternal bacteriocytes, as calculated by subtraction of embryonic chains from whole aphids sample means, in relation to host developmental stage. Results are reported as means ± SD* . (d,e) Modeling of B. aphidicola population dynamics in whole aphids (d) or maternal bacteriocytes (e) during aphid development. A logistic model was applied for the first part of the dynamics (n0 fixed), followed by an exponentially decreasing model. The rupture point (vertical dashed line) was visually determined. The predicted value of the logistic model at this rupture point was used to fix Nmax in the exponentially decreasing model for ensuring continuity and improving the estimation of the population decreasing rate. Population growth, r and decreasing rates, l, are shown on the figure, with their 95% confidence interval. Abbreviations: LE, late embryos; N1 to N4, nymphal stages from 1 to 4; A9-A23, adult time points from day 9 to day 23. Shaded grey area indicates the laying period.