Ramsey, S. D. | Search bioRxiv

bioRxiv2024

Evaluation of efficacy of formic acid and thermal remediation for management of Tropilaelaps and Varroa mites in central Thailand

The western honey bee, Apis mellifera, faces a new threat from the spread of parasitic Tropilaelaps (Tropi) mites, specifically T. mercedesae, which adds additional complexity to an apicultural landscape heavily impacted by Varroa destructor. In this study conducted in central Thailand, we investigated the efficacy of two methods of applying formic acid and a thermal remediation technique in controlling Tropi mites and Varroa, focusing our attention on the reproductive stage of the mites which is restricted to capped brood cells. Results revealed that both formic acid treatments (Formic Pro and liquid formic acid) demonstrated an immediate and substantial reduction in live Tropi and Varroa populations, maintaining near-zero levels for the 3- week duration of the study. In contrast, thermal remediation, employing heating pads, exhibited a more gradual decline, achieving an 85.42% reduction in Tropi mites and a 92.33% reduction in Varroa mites by week three. Notably, heat-treated colonies experienced an unexpected resurgence in mite populations during week two. The findings contribute valuable insights into potential strategies for mitigating the threat of Tropi mites and highlight the urgency of further research to safeguard global honey bee populations.

zoology↗

bioRxiv2022

Kleptocytosis: A Novel Parasitic Strategy for Accelerated Reproduction via Host Protein Stealing in Varroa destructor

Varroa destructor must produce mature offspring within the inflexible nine-day window framing the pupal development of their honey bee host. Missing this deadline renders the foundress mites fitness zero, establishing evolutionary pressure to accelerate reproduction and development. Through micro-computed tomography and modeling Varroas energy budget, we found each egg grows to constitute [~]18% of the foundresss body volume in 30 hours, yet accounts for less than 10% of her energy usage. We hypothesized that this small energy investment is a successful strategy because of Varroas long-ignored ability to traffic intact host proteins. Through gel electrophoresis, concomitant immunodetection, and MS/MS, we detected several intact, bee-derived proteins in mite eggs, including metamorphic proteins (hexamerins) and egg-yolk precursors (vitellogenin and apolipophorin) which likely reduce the parasites direct reproductive investment. We then expressed recombinant Halotag labelled Apis vitellogenin to determine the route conveying exogenous proteins into the mites oocyte. We detected fluorescent vitellogenin in the lyrate organ and observed a tube-like extension of the lyrate organ connecting to the ovum, likely providing an avenue for intact host proteins. Finally, we tested the hypothesis that exogenous proteins maintain functionality in the parasite. Varroa metamorphose despite their inability to produce hexamerins, critical metamorphic proteins. Through label-free quantification of proteins in metamorphosing mites, we observed a hexamerin depletion pattern consistent with usage as a metamorphic amino acid reservoir. We describe this process as "kleptocytosis," denoting movement of stolen intact macromolecules from host to a parasite cell. Given their fixed developmental timeline, this pathway presents a promising target for novel Varroa management strategies. Significance StatementGlobal honey bee health is threatened by the parasitic mite Varroa destructor; its success due in part to its rapid reproduction and accelerated development. By combining biological modeling, micro-computed tomography, fluorescence imaging, and quantitative proteomics, we show that Varroa siphon intact, ostensibly functional host proteins conveying them directly to their oocyte. This avoids the energetically inefficient process of digesting and reconstructing ingested proteins and affords the capacity to utilize proteins that it does not produce de novo facilitating rapid reproduction and accelerated development. We call this process "kleptocytosis," and identify anatomical adaptations which apparently facilitate protein movement. This work exposes a new target in Varroas physiology, providing a promising direction for more effective management strategies.

zoology↗