Long-term presence of emerging pathogens in island honey bee colonies

Honey bees are recognised as the primary pollinators of most agricultural crops and numerous wild plant species worldwide. However, the colony losses reported over recent decades pose a serious threat to this essential ecosystem service. The spread of pathogens has been identified as a significant factor contributing to the decline of honey bee populations. Consequently, there is a considerable interest in expanding our knowledge on the prevalence of emerging pathogens on honey bee colonies, particularly trypanosomatids and neogregarines. Herein, we conducted a spatio-temporal analysis of the prevalence of trypanosomatids (Lotmaria passim and Crithidia mellificae) and a neogregarine (Apicystis bombi) in honey bee populations across the Canary Islands sampled over a 20-year period (1998-2017). We also examined whether pathogen prevalence was associated with the introduction of foreign honey bee queens to the islands and the implementation of a conservation programme of the local Canarian black honey bee. Our results indicate that L. passim has been present in the Canary Islands since at least 1998, whereas C. mellificae was not detected. This finding represents the earliest known global record of the L. passim worldwide. Apicystis bombi was found on several islands during the study period, though at low frequency. The prevalence of L. passim did not exhibit any correlation with the introduction of foreign honey bee queens, unlike other pathogens and parasites such as Nosema ceranae and Varroa destructor. Notably, the implementation of long-standing conservation measures in La Palma was associated with a higher prevalence of L. passim compared to Gran Canaria. These results suggest that L. passim may have been present in the Canary Islands prior to the introduction of foreign honey bees in recent decades. Further analyses of historical samples from additional regions, particularly from geographically isolated areas such as islands, are necessary to untangle the spread history of L. passim in honey bee populations.