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Title: Evaluations of the removal of Varroa destructor in Russian honey bee colonies that display different levels of Varroa Sensitive Hygienic activities

item KIRRANE, MARIA - University College Cork
item De Guzman, Lilia
item Frake, Amanda
item Rinderer, Thomas
item WHELAN, PADRAIG - University College Cork

Submitted to: Journal of Insect Behavior
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2018
Publication Date: 4/17/2018
Citation: Kirrane, M.J., De Guzman, L.I., Frake, A.M., Rinderer, T.E., Whelan, P.M. 2018. Evaluations of the removal of Varroa destructor in Russian honey bee colonies that display different levels of Varroa Sensitive Hygienic activities. Journal of Insect Behavior.

Interpretive Summary: Breeding honey bees to increase resistance to Varroa destructor has been successful with Russian honey bees (RHB). This has been accomplished by breeding for reduced mite population growth. This assessment is a complex procedure which is unsuitable for commercial honey bee breeders. In part, resistance to Varroa results from Varroa sensitive hygiene, the removal of mite infested brood. This study found a strong relationship between the ratios of older mites younger mites to the total mites collected on mite traps placed under colonies. This indicates that the ratios are indirect easy measurements of VSH activity which is also hard to measure. This relationship exists for RHB and any other honey bee stock which displays VSH indicating that evaluations of trapped mites as proportions of older or younger mites can be used to selectively breed honey bees for increased resistance to Varroa. Additionally, measurements of damaged mites have no relationship with levels of mite infestation and are not useful in selection programs.

Technical Abstract: The removal of Varroa destructor was assessed in Russian honey bee (RHB) colonies with known levels of Varroa Sensitive Hygienic (VSH) and brood removal activities. The expression of grooming behaviour using individual bees was also measured using three groups of RHB displaying different VSH levels: low hygiene (RHB-LH, < 35% VSH), medium hygiene (RHB-MH, 35-70%) and high hygiene (RHB-HH, > 70%). The Italian colonies (5.43-71.62% VSH) served as control. Our results demonstrated, for the first time, strong relationships between two hygienic responses (VSH activity measured as percent change in infestation and the actual brood removal of Varroa-infested donor comb) and two measurements of mite fall (trapped old mites/trapped mites or O/T and trapped young mites/trapped mites or Y/T). However, these relationships were only observed in RHB colonies. In addition, the RHB colonies that displayed the highest levels of hygiene (RHB-HH) also groomed longer in response to the presence of a V. destructor mite based on individual bee assays. The large positive regressions between the two hygienic measurements and O/T and their negative regressions with Y/T suggest that the removal of infested brood prevented successful mite reproduction, ultimately suppressing V. destructor infestations in the RHB colonies. Since hygienic measurements did not influence O/T or Y/T in the Italian colonies, the large negative regressions between adult infestations and O/T and large positive regression between adult infestation and Y/T may suggest that both old and young mites emerging with the bees were removed. Nonetheless, this removal was not sufficient to cause a significant decline in mite infestations, in Italian stock. Combined, these observations demonstrate that RHB resistance to V. destructor rests on both an increased hygienic response and the removal of phoretic mites, released by hygienic behaviour, through grooming. Additionally, both resistance traits are reflected in the O/T and Y/T ratios found in trapped mites from RHB colonies. Also, none of the measurements involving mite injuries [trapped injured mites/trapped mites (I/T), injured fresh/fresh mites (IF/F) and injured dry mites/dry mites (ID/D)] were associated with any measurements of hygiene and colony infestations indicating that mite injury is not a good measure of resistance.