The cell invasion preference of Varroa destructor between the original and new honey bee hosts

Authors: LI, WENFENG - Guangdong Institute Of Applied Biological Resources; ZHANG, YI - Guangdong Institute Of Applied Biological Resources; PENG, HUI - Guangdong Institute Of Applied Biological Resources; ZHANG, RUONAN - Guangdong Institute Of Applied Biological Resources; WANG, ZHENGWEI - Guangdong Institute Of Applied Biological Resources; HUANG, ZACHARY - Michigan State University; Chen, Yanping - Judy; HAN, RICHOU - Guangdong Institute Of Applied Biological Resources

Submitted to: International Journal for Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2021
Publication Date: 9/17/2021
Citation: Li, W., Zhang, Y., Peng, H., Zhang, R., Wang, Z., Huang, Z., Chen, Y., Han, R. 2021. The cell invasion preference of Varroa destructor between the original and new honey bee hosts. International Journal for Parasitology. 52:125-134. https://doi.org/10.1016/j.ijpara.2021.08.001.
DOI: https://doi.org/10.1016/j.ijpara.2021.08.001

Interpretive Summary: The Varroa mite is the most serious pest for honey bee colonies. Since shifting its target from the Asian honey bee to its European counterpart, the mite has enacted catastrophic damage to its new host. Over the past few decades, the mechanisms underlying Varroa parasitism have attracted extensive research interest. In order to further our understanding of these complex host-parasite interactions, we conducted a study to investigate whether Varroa mites show a preference during the initial host invasion between the two host species. Our results showed that they display a significant preference for invading the European honey bees during the cell invasion when compared to Asian honey bees. Further chemical analysis revealed that there were qualitative differences in volatile chemical emissions between the two types of the insect, which could also be useful for the development of mite control in the future. The information gained from this study should be of interest to researchers, graduate students, beekeepers, and policymakers worldwide.

Technical Abstract: Honey bees are important pollinators for many kinds of agricultural crops and wild plants, but are facing great threats from pathogens and parasites, especially the Varroa mites Varroa destructor. As an obligate ectoparasite of honey bees, Varroa mites cause severe damage to the hosts by direct feeding on them and transmitting various bee viruses. Cell invasion is the process through which the mother mites enter the cells with worker or drone larvae of a certain age, which is a key step for the parasites to reproduce. Varroa mites display significant host preference during the cell invasion. However, it is still unknown whether the mites show cell invasion preference between the two bee hosts, the Asian honey bee Apis cerana and the European honey bee A. mellifera, although although it is a well-known fact t that V. destructor made its host-shift from its original host A. cerana to A. mellifera over decades ago. By using a series of binary-choice tests on modified four-well arenas, we tested the cell invasion behavior of Varroa mites between the Chinese bee (A. cerana cerana, Acc) and Italian bee (A. mellifera ligustica, Aml) larvae, and the results indicated that V. destructor significantly preferred to invade the cells with Aml worker (drone) larvae, suggesting that the new host was signficantly more attractive to the mites than the original one. Considering the signaling role of insect cuticular hydrocarbons (CHCs) in chemical communication, we compared the differences of CHC composition between Acc and Aml worker (drone) larvae by using gas chromatography-mass spectrometer analysis on the hexane-extracts of larvae body surfaces. The data revealed a remarkable difference between the CHC profiles of the two bee hosts, as though they shared the majority of all CHC compounds. Quantitative comparison of individual CHCs reveals that more significant differences were observed in the methyl-branched alkanes and alkenes (unsaturated CHCs) than in n-alkanes, Aml larvae expressed significantly more methyl-alkanes, while Acc larvae produced quite higher levels of alkenes. The Varroa invasion preference of A. mellifera to A. cerana revealed by our study may explain to some extend its better adaption to the new host and the rapid global population expansion. The differences of CHCs between the two bee hosts provide the foundation for future selection and verification of specific semiochemicals underpinning the host preference of Varroa mites, which could also be useful for the development of mite control in the future.