Monday, December 11, 2006

Chemical mimicry by the ectoparasitic mite Varroa destructor infesting Apis cerana and Apis mellifera

Zachary Y. Huang, bees@msu.edu1, Yves Le Conte, leconte@avignon.inra.fr2, M. Navajas, navajas@ensam.inra.fr3, J. P. Christides4, Z. J. Zeng5, and A. G. Bagnères4. (1) Michigan State University, Department of Entomology, 243 Natural Sciences, East Lansing, MI, (2) UMR 406 INRA/UAPV Ecologie des Invertébrés, Laboratoire Biologie et Protection de l'abeille, Site Agroparc, Domaine Saint-Paul, Avignon, Cedex 9, France, (3) CBGP, INRA, Campus international de Baillarguet, CS 30016, Montferrier-sur-Lez cedex, France, (4) Université de Tours, Faculté des Sciences, IRBI, UMR CNRS 6035, Tours, France, (5) Jiangxi Agricultural University, Honeybee Science Institute, College of Animal Science, Nanchang, Jiangxi, China

The mite Varroa destructor is a honeybee ectoparasite. Its original host is Apis cerana (Ac) in Asia but it has become a severe threat for A. mellifera (Am) in Europe and the rest of the world. Analysis of mitochondrial polymorphism further indicated that Varroa parasiting Ac colonies presented a different haplotype from Varroa parasiting Am colonies, even if the colonies of the two bee species were located in the same place. Contact between the founding Varroa female and Apis larvae prior to cell capping is a key factor in triggering mite reproduction. From the egg and adulthood, mite reproduction involves three life stages, i.e., larvae, protonymph, and deutonymph. Study of chemical signatures at each stage for each sex has demonstrated great sexual dimorphism. Chemical mimicking by the mite probably plays an important adaptative role in the infestation process since the original host Ac has a highly developed capacity for detection whereas the detection capacities of the new host Am are extremely limited. To study factors underlying this chemical mimicking, we performed tests involving transfer of mites from an Ac brood to either another Ac brood or an Am brood, or of mites from an Am brood to either another Am brood or to an Ac brood. The chemical signatures of both Apis nymphs and their Varroa parasites were studied for all 4 transfer situations. Our findings showed that Varroa always mimicked host cuticular components independently of the mitotype origin, even when the mites were transferred to a different host species.

Species 1: Acari Varroidae Varroa destructor (varroa mite)
Species 2: Hymenoptera Apidae Apis mellifera (western hive bee, honey bee)
Species 3: Hymenoptera Apidae Apis cerana (eastern hive bee, Asian honey bee)