How Drones Get Fit for Action

Introduction

Happy New Year Everyone. I hope you are having a lovely time over the holidays and looking forward to the days getting longer and the bee season starting.

My hive scales tell me that the colonies are not eating much of their precious honey stores, but that will change as soon as the queen increases egg laying and the colonies need to provision increasingly more brood. Annoyingly, only one of out of the five hive temperature sensors is working so I can’t look forward to seeing the graphs showing a rise in brood nest temperatures. However, the colony of rescued bees from the wild has a laying queen right now. For two consecutive days, I’ve seen the tell-tale signs of egg laying on the varroa floor—tiny clear wax flakes. Why else would they produce such a costly substance in the middle of winter if they didn’t need to repair brood cells and cap brood?
Although I look forward to opening up hives for the first colony inspections, I’ll not be doing that till I see the first drones of the season flying. That’s my reminder that swarm season will start soon. Nothing will happen without drones on the scene. Having said that, I shall nip in quickly and check on the temperature sensors without too much disruption as soon as its warm enough.
Speaking of drones, what do they do when they’re not out on orientation and mating flights? Have you ever wondered about that? When I was putting together a PowerPoint presentation on drone biology and behaviour I was curious to know more about their lives inside the hive. I checked out some research by Dr Michael Smith¹ and colleagues from 2023 and here is what I discovered. I’ve mentioned drone hyperactivity before in a previous blog but not how I systematically studied the paper.

Reason for Research

Previous drone research has focused on drone behaviour involving mating flights outside the hive. The scientists wanted to learn more about what drones do inside the hive given that they spend most of their short lives there.

How do drones move around the nest? and how do they spend time inside the nest?

Methods used to test these questions

The researchers used observational methods involving 192 newly emerged and marked (tagged) drones in an observation hive at Konstanz University in Germany. Sophisticated cameras and imaging were employed, and data were collected by a video tracking system called BeesBook which was linked to the individual drone tags. The drones were observed constantly throughout the experiment and their movements tracked and recorded for analysis.

The observation hive was illuminated (for the video recording) with infrared light, which bees do not see, so the drones were not confused in finding their way to the hive’s entrance (to which they orientated by going to the bright light coming in the hive’s entrance).

A simulation model of drone movement called accumulation-to-threshold was used for comparison to what was observed. This involved feeding social information into the simulated model and comparing this with what actually happened in real life. Reassuringly, there was a good match with the researchers’ observations.

The major findings of this paper

Like previous researchers, the authors found that for most of the time the drones hung around on the edge of the brood nest doing very little. However, drones had periods of hyperactivity when they moved about faster than the other bees in the colony. In fact, drone speed was several times faster than worker speed on the comb. These bouts of hyperactivity started after the drones reached 7 days of age and they occurred at the same time in the afternoons that drones normally start taking short orientation flights. What was interesting was that all the drones of the same age shared this activity at the same time of day. The length of the in-hive activity depended upon the weather, and if it was good and suitable for mating flights then the time spent inside moving fast increased.

The beginning of these periods of hyperactivity related to the stages of drone sexual maturity. The sperm moves from the testes to the seminal vesicles at around 7-8 days from emergence. Sperm viability peaking at day 7, which is when the bouts of hyperactivity commence. Short orientation flights commence at 6-9 days in preparation for longer flights (1-5km from nest) to drone congregation areas where a lucky drone might mate with a queen when he is over 11- 12 days of age.

By resting on the periphery of the brood nest, before day 7, the drone is conserving his energy for when he needs it most during these energetic mating flights in which only the fastest drone catches up with and mates with a queen.

These findings give us a better understanding of drone behaviour inside the hive and how it relates to preparing for their key roles in providing sperm for colony reproduction, and mating with a queen.

The main questions have certainly been answered and the findings are statistically significant and are very unlikely to have been found by chance. I know this because the probability values are P 0.001. A P value of P 0.05 is considered significant, meaning that there is less than a 5% chance that the same observation would be seen by random chance.

Surprising results

I was surprised initially to learn that drones have bouts of hyperactivity because when I see them inside a hive they are usually ambling slowly along the comb, or hanging out peacefully on the outside of a brood frame. That their movements are synchronized in order to maximize mating opportunities is not a surprise though given the wondrous way that a superorganism works. Every single bee behaviour appears to have evolved to promote a colony’s success in passing on its genes, and in this case drones are working together to prepare to fulfill their roles.

Why the findings of this paper are important

The findings are important because they provide new information in addition to what we already know about honey bees, and in particular the role of drones. This work shows that drones are very important and that they have specialized behaviours inside the nest which prepare them for getting to the drone congregation areas ahead of the queens, and at the right time of the day for their subspecies.

This paper led me to fascinating information about how different subspecies go out on mating flights at different times of the day. Also, some drone subspecies have different lengths of endophalluses. These strategies increase the chances of the different subspecies that occupy the same habitat mating with their own subspecies.

How these findings can help beekeepers better manage their colonies

When beekeepers understand the dynamics of drone production, development, and preparation for mating they know that drones require high energy and good nutrition at every stage of their life cycle. Knowing that even more energy is used up during these bouts of hyperactivity reinforces the need for healthy, disease-free, well- nourished drones.

Some of the following measures may improve management.

• Focus on good nutrition and be alert to poor quality forage and income dearth. Supplement as necessary, especially when drones are developing.
• Reduce exposure to pesticides and varroacides which are known to negatively impact quality of drone sperm. Amitraz (Apivar) and Coumaphos are particularly toxic and harmful.
• Be mindful of culling too many drones during Varroa destructor (varroa) control.
• Promote drone production and provide frames with drone cell foundation.
• Keep virus levels low, and varroa levels below harmful threshold (1000mites/colony).
• Keep disease-free colonies and monitor for Vairimorpha spp. (nosema) which negatively impacts drone sperm.
• In hot climates, protect apiaries from sunshine, and colonies from overheating as extreme heat negatively impacts drone sperm.

Reference:

¹Louisa C. Neubauer, Jacob D. Davidson, Benjamin Wild, David M. Dormagen, Tim Landgraf, Iain D. Couzin, & Michael L. Smith, (2023) Honey bee drones are synchronously hyperactive inside the nest, Animal Behaviour,  https://doi.org/10.1016/j.anbehav.2023.05.018