Comparison Between Apis Cerana And Apis Mellifera In The Host-Parasite Interactions With Varroa Destructor

Honey bees,Apis spp.,are the most important pollinators and play crucial roles in the balance of the ecosystem,sustainable agriculture and food security globally.In recent years,however,losses of the western honey bee Apis mellifera colonies are getting increasingly serious and the population of wild pollinators declines rapidly,which has triggered a lot of attention in the public as well as in the scientific communities.In a wealth of studies,there has been a consensus that an emerging ectoparasitic mite,Varroa destructor,is the principal threatening factor to the health of A.mellifera colonies.The ubiquitous mite originally parasitized in the eastern honey bee Apis cerana colonies and shifted host to A.mellifera when the latter were introduced into Asia,the natural distribution range of the former.As a result of insufficient coevolution,V.destructor has been the most severe biotic threat to A.mellifera worldwide.In the contrast,the ectoparasite shows no apparent damage to its original host A.cerana.Therefore,the notable difference of the susceptibility between the two closely related honey bee species to the same parasite provides an ideal model to study the coevolution and interactions in the host-parasite system.In this study,by comparing the susceptibility between A.cerana and.mellifera to V.destructor,we tried to better understand the interactions between the ectoparasitic mite and its original host.In addition,we hope to reveal the mechanism of host-parasite coevolution from a certain aspect and provide insights into the host specificity.1.The comparison of hygienic ability between A.cerana and A.melliferaTo study the role of honey bee brood and adults in the hygienic behavior,we found that A.cerana brood reacted more rapidly and intensely to benign wounding than A.mellifera.Meanwhile,A.cerana adult workers detected and removed freeze-killed brood consistently faster.This higher efficiency of detection was expressed within the first few hours of exposure.Taken together,the more susceptible brood and more efficient adults may enhance the group immunity.2.The effects of honey bee brood and adults on V.destructor reproductionTo study the antagonistic and complex interactions between the development of honey bee brood and V destructor reproduction,we tried to better understand the evolutionary arms race between host and parasite.By investigating a serious of V.destructor activities for the maintenance and growth of their population,including host finding,parasitism and successful reproduction,we further ascertained the role of honey bee brood and adults in the interactions with V.destructor.The results suggested that immature workers of the mite’s original host,A.cerana,are more susceptible to V.destructor infestations than those of its new host and the delayed development state highly correlated with the removed brood by adults.The invasive haplotype of V.destructor can reproduce in its original worker brood cells but the successful reproduction was prevented by abnormal host development and adult worker activities.The susceptible individuals of A.cerana enable more efficient social immunity and thus contribute to colony survival.This counterintuitive model of group immunity is analogous to the apoptosis in multicellular organisms,which is termed as social apoptosis.3.The relationship between different virulence and reproductive ability of V.destructorBy classifying the differential mortality of the original hosts,we proposed the different virulence of V.destructor.The reproductive ability of V destructor correlated with its virulence.The medium and low virulent ectoparasites showed higher fertility(reproductive rate)than the high virulent ones.Whereas the reproductive success rate and the efficient reproduction peaked in the low virulent ones.The reproductive activities of high virulent V destructor mites performed worst.4.Study on the mechanism of host brood death caused by V.destructorTo study the causes of honey bee brood death,we investigated the internal and external factors.We excluded the altruistic suicide of the brood since no significant up-or down-regulated apoptosis genes were observed on the parasitized hosts.The harm caused by virus infection to host was limited without mite parasitism.However,Deformed wing virus(DWV),Israeli acute paralysis virus(IAPV)and Kashmir bee virus(KBV)carried by V.destructor may play a key role in the delayed development and even the death of hosts.Meanwhile,the lethal mechanism of parasitized A.mellifera and A.cerana brood showed similar:the acute lethal toxicity of IAPV and KBV was likely to be responsible for the dead larvae;the chronic toxicity of DWV most likely caused the death of honey bee prepupae and pupae,5.The beneficial effects of V.destructor on the conservation of pollinator biodiversityV.destructor mites limit the growth and expansion of A.mellifera populations from establishment of wild colonies outside of the natural distribution.V.destructor hence reduces the competition for living space and food resource between the invasive A.mellifera and native pollinators.However,given V.destructor-resistant A.mellifera stock will be available in the near future,their further spread will be inevitable with most likely more severe consequences for native species,especially Asian honey bees.We thus urge taking preventive steps in regulating the trade of resistant stock,while providing efficient control alternatives and promoting established or novel endemic managed pollinators.