Effect of Comb Cell Width on the Activity of the Proteolytic System in the Hemolymph of Apis mellifera Workers

Large cells suppress the reproduction of Varroa destructor

BACKGROUND

The parasitic mite, Varroa destructor has posed a threat to the health and survival of European honey bees, Apis mellifera worldwide. There is a prevailing belief that small comb cells could provide a management tool against Varroa mites. However, the hypothesis that smaller cells can impede Varroa reproduction has not been fully tested. Here, we tested this hypothesis under laboratory conditions by using two distinct Varroa in vitro rearing systems: one involved gelatin capsules of different sizes, specifically size 00 (0.95 mL) versus size 1 (0.48 mL), and the second consisted of brood comb cells drawn on 3D printed foundations with varying cell sizes, ranging from 5.0 mm to 7.0 mm at 0.5 mm intervals.

RESULTS

The results showed that mother mites in size 00 cells had significantly lower fecundity and fertility compared to those in size 1 cells. Interestingly, the reproductive suppression in larger cells could be reversed by adding an extra worker larva. Similarly, gonopore size of mother mites was smaller in size 00 cells, but restored with another host larva. Furthermore, both the fecundity and fertility of mother mites decreased linearly with the size of brood comb cells.

CONCLUSIONS

Our results suggest that the reproduction of V. destructor is hindered by larger cells, possibly because larger brood cells disperse or weaken host volatile chemical cues that are crucial for Varroa reproduction. The insights derived from this study are expected to hold significant implications for the implementation of Varroa management programs. © 2024 Society of Chemical Industry.

Workers of Apis mellifera Reared in Small-Cell Combs Show Higher Activity of the Proteolytic System in Hemolymph than Workers Reared in Standard-Cell Combs in Laboratory Cage Tests

The aim of the study was to compare the activities of proteases and their inhibitors in the hemolymph of honeybee workers reared in small-cell combs (SMC) and standard-cell combs (STC) in laboratory cage tests. The analyses conducted in laboratory conditions facilitated assessment of the impact of the comb cell width (small vs. standard) along with eliminating the influence of many environmental factors on the results. The width of the comb cells in which the workers were reared had a significant effect on the protein concentrations and proteolytic system activities in the hemolymph. Irrespective of the age of the workers, higher protein concentrations were found in the hemolymph of the SMC workers. In turn, the activities of proteases and their inhibitors in the hemolymph of 1-day-old bees were higher in the STC workers. In older bees, aged 7-21 days, activity was higher in the SMC workers. The role of the considerable cell width variability in natural combs that were built without the use of an artificially produced wax foundation is worth investigating. It is highly probable that the impact of the comb cell width on the features of workers reared in these combs modifies the age polyethism in the worker caste as well. The investigation results of one-season studies of honeybees could be seriously affected by random factors. To reduce the risk of these effects, it is advisable to continue experiments over a few consecutive years.

Effect of Rearing in Small-Cell Combs on Activities of Catalase and Superoxide Dismutase and Total Antioxidant Capacity in the Hemolymph of Apis mellifera Workers

Honeybee nests constructed without man-made wax foundation have significantly more variability of cell widths/sizes than those in commercially-kept colonies. The effects of this natural variability in comb cell widths on individual and colony traits have not been explained to date. The investigation of this problem can lead to new findings about the biology, physiology, and possibly, the evolution of the honeybee. The aim of the study was to compare the catalase and superoxide dismutase activities and the total antioxidant capacity levels in the hemolymph of honeybee workers reared in small-cell combs and standard-cell combs in colonies kept simultaneously on standard- and small-cell combs. The ratio of the small-cell combs to the standard-cell combs in the nest was 1:1. The workers reared in small-cell combs were characterized by higher antioxidant activities in the hemolymph than those reared in standard-cell combs. Consequently, their hemolymph had a greater antioxidant capacity, which indicates that they may be better predisposed to be foragers than workers reared in standard-cell combs. To describe the physiological differences between worker bees reared in small- and standard-cell combs in the same colony, the role of the considerable variation in the cell width in natural combs built without the use of artificially produced wax foundation is worth elucidating. The comparison of the apiary and cage experiments indicated that changes in antioxidant activities predominantly result from worker activities, especially those requiring the intensification of metabolism, rather than the age of the worker bees. To reduce the impact on the results of random environmental factors potentially present in one-season studies of honeybee research, investigations should preferably be carried out over a few consecutive years.