Kleptocytosis: Comparative Proteomics and Functional Imaging Show Varroa destructor Co-Opts Intact Host Proteins for Rapid Reproduction.

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 mite’s fitness zero, establishing evolutionary pressure to accelerate reproduction and development. Through micro-computed tomography and modeling Varroa’s energy budget, we found each egg grows to constitute ~18% of the foundress’s 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 Varroa’s 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 parasite’s direct reproductive investment. We then expressed recombinant Halotag labelled Apis vitellogenin to determine the route conveying exogenous proteins into the mite’s 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 functional molecules from host to a parasite cell. Given their fixed developmental timeline, this pathway presents a promising target for novel Varroa management strategies.