Unique Brood Ester Profile in Varroa Destructor Resistant European Honey Bee Population
Varroa destructor poses a significant threat to Apis mellifera, often leading to colony death within two years if untreated. A population of honey bees on Gotland, Sweden, has survived with minimal chemical intervention for over 25 years, exhibiting traits that reduce the reproductive success of Varroa. This study aims to explore the brood ester pheromone (BEP) profile of this resistant population and its potential role in mitigating Varroa infestation.
Background
Varroa mites depend on honey bees for nourishment and reproduction, primarily within the brood cells. Their presence is linked to the transmission of viruses like the Deformed Wing Virus (DWV), which diminishes bee health and increases colony mortality. Conventional treatments for Varroa, while effective, can harm bee health and lead to resistance. Selective breeding for Varroa resistance has shown promise but often targets adult bee behaviors rather than brood characteristics.
The Gotland Population
The honey bee population on Gotland has demonstrated a unique resistance mechanism, allowing only about 50% of Varroa mothers to produce viable offspring. This trait appears to be genetic rather than a result of mite virulence. The focus of this study is to understand how brood characteristics contribute to this resistance, particularly through chemical communication via BEP profiles.
Chemical Signaling and Brood Ester Pheromones
BEPs are volatile compounds produced by developing brood, serving to communicate with adult bees about brood age and caste. The same compounds can act as kairomones for Varroa, signaling when to invade brood cells. Changes in the BEP profile could disrupt this communication, affecting mite reproduction.
Methods
We established twelve honey bee colonies using six non-resistant and six resistant queens. The brood was monitored at various time points post-capping to analyze the BEP profile using gas chromatography. We compared the quantity and timing of specific BEP compounds between the resistant and non-resistant populations.
Results
The resistant population produced significantly lower amounts of BEP compounds, particularly at the crucial 0-hour post-capping mark, indicating a potential chemical camouflage strategy. This reduction in BEP production may hinder the mites' ability to synchronize their reproduction with brood development.
Discussion
The findings suggest that the Gotland population's resistance may stem from an evolutionary adaptation in chemical signaling. By producing fewer BEP compounds, the honey bees may make it more challenging for Varroa to initiate reproduction, thus contributing to the population's long-term survival against infestation.
Conclusion
This study highlights critical differences in the BEP profiles of Varroa-resistant honey bees compared to non-resistant counterparts. Understanding these mechanisms provides valuable insights into potential breeding strategies for enhanced Varroa resistance, fostering healthier bee populations globally. Further research is needed to explore the implications of these findings on brood development and the broader host-parasite dynamic.
