Integrated Pest Management Strategies to Control Varroa Mites and Their Effect on Viral Loads in Honey Bee Colonies

Innovations in Varroa mite management

Varroa mites, the main pest of honey bees, are notoriously difficult to control. We present a novel approach to mite management emphasising the role of immigration. We argue that how mite numbers increase within the colony determines the most effective varroa management techniques. That is, varroa infestations go through phases, where their rate of increase is either driven by varroa reproduction (Chronic phase) or is strongly influenced by immigration into the hive (Acute phase). Identifying chronic and acute phases will enable current varroa control methods to be better targeted. For example, control methods reducing reproduction rates will be most effective during the chronic phase. Identifying when immigration is important to varroa in-hive population increases (acute phase) may enable existing bee management techniques, for example, those that limit the access of some bees into hives, to be co-opted into varroa management. This change in perspective emphasises that in-hive varroa control will be improved by understanding the subtleties of how and when varroa enter hives; it will also identify other gaps in our knowledge of varroa's behavioural ecology that could lead to new varroa control methods. Therefore, this novel approach to mite management will enable Integrated Pest Management to be better tailored to this pest.

The status of pyrethroid resistance mutation frequencies in Varroa destructor populations in the most important beekeeping areas of Türkiye

The Varroa destructor (hereafter referred to as Varroa) is a major pest of honeybees that is generally controlled using pyrethroid-based acaricides. However, resistance to these insecticides has become a growing problem, driven by the acquisition of knockdown resistance (kdr) mutations in the mite's voltage-gated sodium channel (vgsc) gene. Resistance mutations in the vgsc gene, such as the L925V mutation, can confer resistance to pyrethroids like flumethrin and tau-fluvalinate. Monitoring genotypic resistance through molecular mutation screening is crucial for tracking and mitigating resistance spread. In this study, the frequency of resistance mutations in the vgsc was examined using a Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) approach in Varroa populations sampled throughout the Mediterranean, Aegean, and Black Sea regions of Türkiye. Considering all the samples analyzed, the results demonstrated a mean resistance allele frequency of 83.29%, indicating a relatively high frequency of resistant alleles. We observed 94.58%, 85.71%, and 69.58% resistant allele frequencies in populations sampled from the Mediterranean, Aegean, and Black Sea regions, respectively, in our study. The results of our investigation demonstrated substantial regional variations in the frequencies of resistant alleles among Varroa populations throughout Türkiye, with notably elevated resistance levels observed in the Mediterranean and Aegean regions. Due to the significant resistance mutation frequency differences between both provinces and regions, long-term monitoring of resistance alleles and the planning of regional control strategies are required for effective control of this pest.

Selection and Multiplexing of Reverse Transcription-Quantitative PCR Tests Targeting Relevant Honeybee Viral Pathogens

Verifying the inclusivity of molecular detection methods gives indications about the reliability of viral infection diagnosis because of the tendency of viral pathogens to undergo sequence variation. This study was aimed at selecting inclusive probes based on reverse transcription-quantitative PCR (RT-qPCR) assays for the diagnosis of the most widespread and detrimental viruses infecting honeybees, namely the acute bee paralysis virus (ABPV), the black queen cell virus (BQCV), the chronic paralysis bee virus (CBPV), the deformed wing virus variants A (DWVA) and B (DWVB), and the sacbrood virus (SBV). Therefore, previously described detection methods were re-evaluated in silico for their specificity and inclusivity. Based on this evaluation, selected methods were modified, or new ones were designed and tested in duplex RT-qPCR reactions. The limits of detection (LODs), effect of multiplexing on sensitivity and the viral RNA quantification potential in bees and hive debris were assessed. This study made available diagnostic assays able to detect an increased number of virus variants compared with previously described tests and two viral pathogens in a single PCR reaction.