A step towards understanding the link between honey bee (Apis mellifera) worker longevity and Varroa resistance

Honey bee, Apis mellifera (Hymenoptera: Apidae), worker longevity is crucial for colony productivity and survival. A recent study showed a 50% decrease in worker longevity over the past 5 decades that predicted overwinter and annual colony losses. Trait selection may inadvertently result in stocks with variable worker lifespan. This has not been examined for Varroa resistance. In a previous study, we established an observation hive to determine the lifespan and foraging onset of workers from Varroa-resistant (POL and RHB) and commercial (IHB) stocks. We found that POL and RHB workers lived significantly longer and started foraging much later compared to IHB workers. This increased lifespan might be associated with vitellogenin (vg) expression, a longevity marker. Thus, we hypothesized that workers from Varroa-resistant and commercial stocks have different vg expression. In this study, we quantified fat body vg expression of 1-, 7-, and 14-day old workers from the three stocks. We found that vg expression varied between ages and stocks. Expression of vg was the highest in POL workers at 7 days but showed a decline at 14 days. In contrast, RHB workers had the lowest vg expression at 7 days, but showed an increase at 14 days. IHB workers had a mean vg expression that was higher than that of RHB workers at 7 days, and the highest at days 14. However, the variance in their vg expression is too great to derive any conclusions. Therefore, more colonies per stock, and more individuals per colonies need to be sampled.