Parasite host shifts can impose a high selective pressure on novel hosts. Even though
the coevolved systems can reveal fundamental aspects of host–parasite interactions,
research often focuses on the new host–parasite relationships. This holds true for
two ectoparasitic mite species, Varroa destructor and Varroa jacobsonii, which have
shifted hosts from Eastern honey bees, Apis cerana, to Western honey bees, Apis
mellifera, generating colony losses of these pollinators globally. Here, we study infestation
rates and reproduction of V. destructor and V. jacobsonii haplotypes in 185
A. cerana colonies of six populations in China and Thailand to investigate how coevolution
shaped these features. Reproductive success was mostly similar and low,
indicating constraints imposed by hosts and/or mite physiology. Infestation rates
varied between mite haplotypes, suggesting distinct local co-evolutionary scenarios.
The differences in infestation rates and reproductive output between haplotypes did
not correlate with the virulence of the respective host-shifted lineages suggesting
distinct selection scenarios in novel and original host. The occasional worker brood
infestation was significantly lower than that of drone brood, except for the V. destructor
haplotype (Korea) from which the invasive lineage derived. Whether mites infesting
and reproducing in atypical intraspecific hosts (i.e., workers and queens) actually
predisposes for and may govern the impact of host shifts on novel hosts should be
determined by identifying the underlying mechanisms. In general, the apparent gaps
in our knowledge of this coevolved system need to be further addressed to foster
the adequate protection of wild and managed honey bees from these mites globally.