Effect of exposure to insecticides on <i>N. ceranae</i> spore production.

<p>The spore production in the digestive tract (midgut and rectum) was assessed at 20 days p.i. Data represent the mean numbers of spores/honeybee (×10⁶ +/− standard deviation, sd) from 15 honeybees, 20 days p.i. Asterisks indicate the level of significance at p<0.05 (*) and p<0.01 (**).</p

Effect of <i>N. ceranae</i> infection on ECOD (A) and GST (B) activities at 10 days p.i. in midgut and fat body of honeybees.

<p>Data represent the mean of specific activity (nmoles/min/mg of proteins +/− standard deviation, sd) from 6 replicates (45 honeybees/replicate) of control and infected honeybees. Asterisks indicate the level of significance at p<0.01 (**). ECOD: 7-ethoxycoumarin-O-deethylase; GST: Glutathione-S-Transferase.</p

Effect of <i>N. ceranae</i> infection on honeybee sensitivity to insecticides.

<p>(A) Percentage of honeybee mortality of (i) uninfected control (light green square), (ii) <i>N. ceranae</i>-infected (dark green square), (iii) uninfected and chronically exposed to fipronil (light red circle), (iv) uninfected and chronically exposed to thiacloprid (light blue triangle), (v) <i>N. ceranae</i>-infected then chronically exposed to fipronil (dark red circle) and (vi) <i>N. ceranae</i>-infected then chronically exposed to thiacloprid (dark blue triangle). The arrow indicates the time of exposure to insecticides (10 days p.i.). Data represent the percentage of cumulative mortality calculated from 3 cages, each containing 50 honeybees. The means of fipronil (B) and thiacloprid (C) consumptions (pg or ng/bee/day +/− standard deviation, sd) were daily-monitored until 20 days p.i. for both infected (dark red or blue) and uninfected (light red or blue) honeybees.</p

Infection monitoring.

<p>(A) Semi-thin sections of midgut epithelium of control (left) and infected (right) honeybees stained with toluidin blue. Arrows indicate <i>N. ceranae</i> foci. Bar = 25 µm. (B) Effect of <i>N. ceranae</i> infection on sucrose consumption. Data represent the mean of cumulative sucrose consumption (mg/bee +/− standard deviation, sd) from 9 replicates, each containing 50 honeybees.</p