Figure 1.
Colony development for adult bees, worker brood, and Varroa destructor mites.
The daily number of individual adult bees (dotted line) and worker brood (striped line) was modelled over one year. The number of mites (solid line) was modelled as being the second year of mite infestation with a starting population of 100 mites in the first year. Figure was redrawn from Martin [9].
Figure 2.
Expected infestation levels of Varroa destructor manipulated using acaricide treatment.
Infestation levels of V. destructor (mites/bee) were manipulated using acaricide treatment applied at different moments (July, August, September or not treated at all). For the expected mite infestation, we used a simplified curve from mite infestation in Figure 1, with an exponential increase in mite infestation until October, after which the infestation remained equal. Efficacy of the acaricide Thymovar (July, August, September) was assumed to be 90%, while efficacy of oxalic acid (December) was assumed to be 95%.
Figure 3.
Mean daily mite fall in 2005/2006 (A) and 2006/2007 (B).
Colonies were treated with Thymovar® in July (white bars), August (grey bars), September (dark grey bars), or not treated at all (black bars). All colonies were treated in December using oxalic acid (3%). Letters denote significant differences between treatments within each month. No letters mean no significant differences between treatments were found. Differences between months were not given.
Figure 4.
Bee survival as a function of time and treatment in 2005/2006 (A) and 2006/2007 (B).
Bee survival (fraction d100) was the predicted fraction of bees that was still alive at the age of 100 days, and calculated using a Cox Proportional Hazards Model. Time was the marking date of the cohort (scatterplot). Different months of acaricide application show the treatments, where letters denote significant differences (over all marking dates).
Figure 5.
Mean number of capped brood cells in 2005/2006 (A) and 2006/2007 (B).
Colonies were treated with Thymovar® in July (white bars), August (grey bars), September (dark grey bars), or not treated at all (black bars). Number of capped brood cells between December 2005 and March 2006 were not measured due to cold winter temperatures. Letters show significant differences between months.
Figure 6.
Bee survival as a function of brood in 2005/2006 (A) and 2006/2007 (B).
Bee survival (fraction d100), the predicted fraction of bees that was still alive at the age of 100 days, as function of the number of capped brood cells for the different months of acaricide application. Symbols show means per marking day.
Figure 7.
Winter survival as a function of bee survival in November 2005 (B) and 2006 (B).
Fraction of frames occupied with bees in a colony in April in relation to bee survival at 100 days for the cohorts marked in November 2005 (A) and November 2006 (B). We used the data for November as an example, the relationship is similar for all days of marking, the trend only showed lower bee survival for cohorts marked earlier. Inserts show the differences in the fraction of frames occupied between for the different treatments (timing of acaricide application, NT = not treated). Letters indicate significant differences.