Molecular Pathogens 2024, Vol.15, No.3, 129-141 http://microbescipublisher.com/index.php/mp 130 understanding of the factors contributing to honeybee declines and to highlight potential strategies for mitigating these threats. The study will explore the interactions between different stressors and their cumulative impact on honeybee health, as well as discuss practical measures that can be implemented to support honeybee populations and ensure the sustainability of pollination services. 2 Pathogens Affecting Honeybee Populations 2.1 Viral pathogens Viral pathogens are a significant threat to honeybee populations, with Deformed Wing Virus (DWV) being one of the most prevalent and destructive. The spread of DWV is closely linked to the parasitic mite Varroa destructor, which facilitates the transmission of the virus among bees. The mite's role in the global epidemic of DWV has been well-documented, showing that the virus has spread rapidly from European honeybees (Apis mellifera) to other regions, driven by trade and movement of bee colonies (Giacobino et al., 2016). The interaction between Varroa mites and DWV has transformed the virus from a relatively benign pathogen into a highly virulent one, leading to significant colony losses (Nazzi et al., 2012). Studies have shown that the presence of Varroa mites increases the prevalence and load of DWV, reducing viral diversity and leading to the dominance of a single, more virulent strain (Martin et al., 2012). 2.2 Bacterial infections Bacterial infections, while less frequently discussed in the provided data, also pose a threat to honeybee health. One notable bacterial pathogen is Nosema apis, a microsporidian that affects the digestive system of bees. In a survey conducted in Kenya, Nosema apis was found at several sites, indicating its presence in honeybee populations (Muli et al., 2014). Although the impact of Nosema apis on colony size and survival was not as pronounced as that of Varroa mites and viruses, its presence still warrants attention as part of the broader spectrum of pathogens affecting honeybees. 2.3 Fungal diseases Fungal diseases, particularly those caused by Nosema species, are another concern for honeybee populations. Nosema apis and Nosema ceranae are microsporidian fungi that infect the gut of honeybees, leading to dysentery and reduced colony productivity. The survey in Kenya identified Nosema apis at multiple locations, suggesting that fungal infections are present but not yet causing significant colony declines (Muli et al., 2014). The interaction between fungal pathogens and other stressors, such as environmental changes and parasitic mites, could exacerbate their impact on honeybee health. 2.4 Parasitic infestations Parasitic infestations, particularly by Varroa destructor, are among the most critical threats to honeybee populations. Varroa mites not only cause direct damage by feeding on bee hemolymph but also act as vectors for various viral pathogens, including DWV (Wilfert et al., 2016). The mites' ability to spread rapidly and their increasing resistance to chemical treatments have made them a formidable challenge for beekeepers worldwide (Mondet et al., 2020; Traynor et al., 2020). Research has shown that Varroa mites destabilize the within-host dynamics of DWV, leading to lethal levels of the virus and contributing to colony collapse (Nazzi et al., 2012). Additionally, Varroa infestations have been linked to alterations in bee physiology, such as impaired water regulation, which further compromises bee survival (Annoscia et al., 2012). Efforts to breed Varroa-resistant honeybee populations have shown promise, with certain traits like brood removal and reduced mite reproduction being identified as key factors in natural resistance (Figure 1) (Mondet et al., 2020; Grindrod and Martin, 2021). The research of Grindrod and Martin (2021) presents a detailed framework for understanding the development of Varroa resistance in honeybee colonies. Central to this framework is the increased detection of mites by resistant bees, leading to several defensive behaviors and outcomes. Resistant bees demonstrate a higher rate of recapping infested cells and removing infested brood, which significantly reduces the number of viable mite offspring. This is depicted by the average recapping rates and brood removal percentages, which are higher in resistant bees compared to susceptible ones. Additionally, mite infertility rates are higher in resistant colonies, contributing to a
RkJQdWJsaXNoZXIy MjQ4ODYzNA==