Date of Award

1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Entomology

First Advisor

Thomas E. Rinderer

Abstract

Comparative resistance or tolerance of four stocks of Apis mellifera L. to Varroa jacobsoni Oudemans, Acarapis dorsalis Morgenthaler, Acarapis externus Morgenthaler and Acarapis woodi (Rennie), was investigated using choice (bioassay) and field experiments. A. m. carnica from Yugoslavia (ARS-Y-C-1), A. m. carnica from Canada (Hastings), F$\sb1$ hybrid between ARS-Y-C-1 and Hastings and a general Louisiana stock were evaluated. A tolerance index showed that Hastings, ARS-Y-C-1 and F$\sb1$ hybrid exhibited some degree of tolerance to V. jacobsoni. These stocks lived longer with higher levels of Varroa infestation in worker pupae and on adult honey bees. Louisiana stock was more susceptible to Varroa infestation showing an earlier death with lower levels of infestation. Regardless of the stock, Varroa had similar reproductive success based on the number of mites per infested pupa (1 to 10 mites), number of foundress Varroa per infested pupa (1 to 3 females), number of progeny per female (0 to 5 progeny), number of progeny per infested pupa (0 to 7 progeny), and proportion of infested pupa containing infertile foundresses (0 to 47%). Apparently, differences in the duration of the capped stage of the four stocks did not influence the ability of Varroa to reproduce. ARS-Y-C-1 stock had the longest capped period and the shortest was observed in the F$\sb1$ hybrid. Louisiana stock seemed to have a better grooming behavior than the three other stocks as shown by the higher number of recovered dead Varroa mites. However, this characteristic did not influence the stock's ability to tolerate mite infestations. ARS-Y-C-1 and the F$\sb1$ hybrid also showed considerable resistance to A. woodi. Colonies of these stocks consistently maintained about 10% tracheal mite infestations in two field trials. This level is well below the level (25%) reported to cause economic damage in honey bees. Using a bioassay, resistance to A. woodi displayed by ARS-Y-C-1 stock was comparable to that of Buckfast and their reciprocal hybrids. Louisiana and Hastings stocks had the highest levels of tracheal mite infestation. A. dorsalis was most prevalent in the Hastings stock and levels of A. externus were higher on ARS-Y-C-1, F$\sb1$ hybrid, and Louisiana stocks.

Pages

169

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