## 3 Results
### Virology  
Multiplex PCR results show viral co-infections (DWV-A, DWV-B, BQCV, ABPV, KBV, and IAPV with higher viral loads when honeybees were highly infested by varroa. A significant difference in viral loads (copies/actin) between infested and control groups was observed at each sampling time (\(p\) = 0.013, 0.036, 0.004, and \(<\)0.0001; \(t\)-test, Mann-Whitney and linear model) except for ABPV (Figures 3-5). Viral loads were significantly higher (\(p<0.05\)) in late September than in late July for DWV-A and BQCV (Figures 3a and 4a). There was also a trend toward an increased viral load throughout time for KBV and ABPV (Figures 4b and 5a) but not for DWV-B and IAPV. The ratios (copies/actin) of DWV-A, DWV-B, BQCV, ABPV, KBV, and IAPV in control hives were near zero or non-detectable over time (from late July to late September) (Table S4). DWV-A loads were significantly higher in infested hives at each time point (\(p<0.05\), Mann-Whitney test) than in the controls, with a significant increase (\(p=0.001\), Wilcoxon test) over time (from late July to late September) (Figure 3a). In July, most infested hives had DWV-A loads that were near zero, except for hives No. 345 and No. 593, with ratios of 2.33 and 3.11, respectively (Table S4). In late September, DWV-A ratios varied from 16.99 to 112.90 in the infested hive group (Table S4). Figure 2: Sugar (glucose and trehalose) concentrations in hemolymph through time. On 18 September 2019, highly infested hives showed a significantly lower concentration of combined sugars in hemolymph compared to control hives (\(\lx@math@degree\), \(p<0.001\), a priori contrasts in LMM). Figure 4: Viral loads in in honeybees of highly infested and control hives over time: (**a**) BQCV loads (copies/actin); (**b**) KBV loads (copies/actin). Viral copies/actin for BQCV and KBV were significantly different between the two studied groups (*, \(p\) < 0.001, linear model and Mann–Whitney test) at each period of the cohort study. There was a great increase of BQCV copies/actin in highly infested hives over time (*, \(p\) < 0.001, linear model). Figure 3: DWV loads on July and September in honeybees of highly infested and control hives: (**a**) DWV-A loads (copies/actin); (**b**) DWV-B loads (copies/actin). Overall, a predominance of DWV variant A is seen. DWV-A and DWV-B copies/actin were significantly higher in infested hives than in controls (*, \(p\) < 0.05, Mann–Whitney test), with a significant increase over time (**, \(p\) = 0.001, Wilcoxon test) for DWV-A. For each sampling time, DWV-B loads were significantly higher in the infested group than in the control (\(p<0.05\), Mann-Whitney test) (Figure 3b). Throughout the experiment (from late July to late September), the DWV-B loads in the infested group remained unchanged (\(p>0.10\), Wilcoxon test) (Figure 3b), with ratios (copies/actin) from 0.76 to 17.65 (Table S4). BQCV loads was significantly different between the two studied groups (\(p<0.001\), linear model) (Figure 4a). From late July to late September, there was a great increase of BQCV loads in highly infested hives (\(p<0.001\), linear model) (Figure 4a), with ratios (copies/actin) varying from 3.70 to 29.11 and reaching up to 170.36 for the hive No. 522 (Table S4). KBV loads from the hives with severe parasitic loads were significantly higher than the controls (\(p<0.001\), Mann-Whitney test) and without an increase over time (\(p>0.05\), Wilcoxon test) (Figure 4b). In late July, KBV ratios were relatively low, from 2.66 to 5.63 in highly infested hives (Table S4). In late September, ratios remained similar to the first time point for most hives: ratios were from 4.49 to 31.38 but were much higher in the hive No. 522, with a ratio of 65.02 (Table S4). In late September, ABPV ratios were 8.13 and 11.98 in infested hives No. 522 and No. 505 (Table S4). There were no significant differences between the two studied hive groups at each time point (\(p>0.10\), Mann-Whitney test) nor a significant increase in time (\(p=0.27\), Wilcoxon test) (Figure 5a).