Submitted to: Insect Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/2012
Publication Date: 1/15/2013
Citation: Cabrera Cordon, A.R., Shirk, P.D., Duehl, A.J., Evans, J.D., Teal, P.E. 2013. Variable induction of vitellogenin genes in the varroa mite, Varroa destructor (Anderson & Trueman) by the honeybee, Apis mellifera L, host and its environment. Insect Molecular Biology. 22(1):88-103.
Interpretive Summary: The varroa mite is a major parasite pest of the honey bee in North America. Scientists at the USDA ARS, Center for Medical, Agricultural and Veterinary Entomology identified the genes for two vitellogenin proteins (Vgs) that function as major components of yolk in the eggs of the varroa mite. A sensitive bioassay was developed based on the transcripts for the Vgs that presents a method for assessing the reproductive state of these mites. The levels of Vg transcripts were found to be tightly linked with the metamorphosis of the bee larval. This bioassay will provide a means of testing various cues from the bee, its cell environment and various hormonal stimulants to control or disrupt the reproduction of the pest varroa mites.
Technical Abstract: Transcript levels of vitellogenins (Vgs) in the varroa mite, Varroa destructor (Anderson & Trueman) were variably induced by interactions between the developing honeybee as a food source and the capped honeybee cell environment. Transcripts for 2 Vgs of varroa mites were sequenced and putative Vg protein products characterized. Sequence analysis of VdVg1 and VdVg2 proteins showed that each had greater similarity with Vg1 and Vg2 proteins from ticks respectively than between themselves and were grouped separately by phylogenetic analyses. This suggests there was a duplication of the ancestral acarine Vg gene prior to the divergence of the mites and ticks. Low levels of transcript were detected in immature mites, males and phoretic females. Following cell invasion by phoretic females, VdVg1 and VdVg2 transcript levels were upregulated after cell capping to a maximum at the time of partial cocoon formation by the honeybee. During oviposition the 2 transcripts were differentially expressed with higher levels of VdVg2 being observed. A bioassay based on assessing the transcript levels was established and experimentally, increases in VdVg1 and VdVg2 transcripts were induced in phoretic females when they were placed inside a cell containing a early metamorphosing last instar bee but not when exposed to the metamorphosing bee alone. The variable response of Vg expression to food source as well as environmental cues within the capped cell demonstrates that perturbation of host-parasite interactions may provide avenues to disrupt the reproductive cycle of the varroa mites and prevent varroasis.