During her mating flight, the queen will leave the hive and be mated with, mid-air, with on average, a dozen drones. This flight provides her with enough sperm to fertilize generations of eggs. But when the queen fails to lay enough fertilized eggs to maintain the population, the death of the colony is ensured. The phenomenon of queen failure is a worsening problem for commercial beekeepers. Whereas in past years, queens could be kept for 2 to 3 years, at present it is not uncommon for some operations to replace queens after as little as 6 months.
As there are no observable symptoms to queen failure, the underlying causes are not well understood. It is believed that several factors play a role, such as varroa and virus’s, pesticide and miticide exposure and environmental conditions, however the exact dynamics remain largely a mystery. Various research projects are helping to provide insight into this important issue.
Temperature and pathogens
One such study, lead by Dr Allison McAfee from the University of British Columbia, sought to investigate how extreme heat, cold and pesticide exposure can impact stored sperm viability. The research team firstly identified specific proteins that are heightened in queens exposed to conditions of cold (1 hour at 4°C), heat (1 hour at 40°C), and pesticides. This enabled them to identify any correlation between exposure to these conditions and queen reproductive performance. They then analysed a sample of both successful and failed queens and discovered that the failed queens had higher expressions of heat shock and pesticide protein markers, than the otherwise successful queens. Interestingly, cold exposure didn’t have an impact.
It is surmised that the logistical operations of queen replacement may be responsible for diminished sperm viability. Queens are a booming business, and once queens have been sold by breeders, they will often spend many hours in cargo holds and warehouses, before being placed in their new colonies. During this trip, they are not able to regulate their body temperatures as they naturally would. Whereas in a hive environment, temperatures are regulated by worker bees fanning and activating their flight muscles, in transit this isn’t possible.
Virus
Various viral infections have been shown to heavily impact the biology of queens, and thus, their reproductive output.
In 2022, a team from British Columbia lead by Dr Agigail Chapman, conducted a research project aimed at investigating the threat of virus’s on social insect reproduction, with honey bee queens serving as the model social insects. In a sample of queens obtained from 10 commercial operations, they found a correlation between high levels of natural viral infection and decreased ovary mass.
«Failed (poor quality) queens displayed higher levels of viral infection, reduced sperm viability, smaller ovaries, and altered ovary protein composition compared to healthy queens.»
(Chapman, 2022)
While the direct physiological impact of virus’s is more evident, the indirect impact is often overlooked. Viral infections can indirectly hinder reproductive capacity by activating a trade-off between the reproductive and immune systems. As both processes require substantial energy resources, reproductive capacity will often be reduced when energy is required for the immune system.
Drones
The burden of queen failure is often assigned solely to the queen. However, the role of drones is just as significant, as healthy drones are necessary in producing and transferring viable sperm. When drones are exposed to pathogens such as agricultural pesticides, the viability of their sperm suffers.
Researchers from the University of Bern examined the viability of sperm in drones that were fed pollen containing neonicotinoid pesticides, compared to drones fed pesticide-free pollen (Straub et al., 2016).
The study revealed a significant decrease of 39% in the number of live sperm within drones that consumed the pesticide laced pollen. Additionally, the drones fed pesticide-laden pollen exhibited a notable reduction in their lifespan when compared to the control group.
As with all things in the colony, these factors do not operate independently, and the impact of one is often amplified by another. The more research undertaken in this field, the better stakeholders, such as policy makers, farmers, beekeepers and the public are equipped to protect and nurture the bees.
Resources
Alison McAfee, Joseph Milone, Abigail Chapman, Leonard J. Foster, Jeffery S. Pettis, David R. Tarpy. Candidate stress biomarkers for queen failure diagnostics. BMC Genomics, 2020; 21 (1),
https://bmcgenomics.biomedcentral.com/articles/10.1186/s12864-020-06992-2
Pettis et al. Colony failure linked to low sperm viability in honey bees (Apis mellifera) queens and an exploration of potential causative factors, 2020,
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0147220
Abigail Chapman, Esmaeil Amiri, Bin Han, Erin McDermott, Olav Rueppell, David R. Tarpy, Leonard J. Foster & Alison McAfee. Fertility costs of cryptic viral infections in a model social insect, 2022,
https://www.nature.com/articles/s41598-022-20330-4
Lars Straub, Laura Villamar-Bouza, Selina Bruckner, Panuwan Chantawannakul, Laurent Gauthier, Kitiphong Khongphinitbunjong, Gina Retschnig, Aline Troxler, Beatriz Vidondo, Peter Neumann and Geoffrey R. Williams. Neonicotinoid
insecticides can serve as inadvertent insect contraceptives, 2016,
https://royalsocietypublishing.org/doi/10.1098/rspb.2016.0506