Veterinary Science Collected Works - Theses
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ItemThe Likely Effect of Varroa destructor on Australian Honey Bee Populations( 2021)Varroa destructor, an invasive ectoparasitic mite of honey bees, is believed to be responsible for a large proportion of reported honey bee deaths globally. Australia remains the only Varroa-free country in the world with a beekeeping industry and horticulture sector reliant on Apis mellifera, the European honey bee. This thesis addresses issues essential to prevent the introduction of Varroa into Australia and better manage Varroa if an incursion (and then establishment) were to occur. The managed honey bee population in Australia is unusual, compared with other livestock industries, because a large sector of the industry (hobby beekeepers) are concentrated in locations where incursions of exotic diseases are likely to occur — urban areas adjacent to sea and international airports. For this reason, hobby beekeepers play an important role in early detection of honey bee diseases and limiting the spread of these diseases once an incursion has occurred. Hobby beekeeper networks need to be documented and appropriate communication and biosecurity resources developed for this sector of the industry to ensure roles and responsibilities are clearly defined (Chapter 3). A quantitative assessment of the Sugar Shake Team surveillance program for Varroa surveillance using scenario tree methods was made in Chapter 4 showing that if one of the 23,300 feral and managed apiariesin the Melbourne Metropolitan area were infested with Varroa there was only a 0.40% chance that it would be detected using the Sugar Shake Team surveillance program during one of the three or four surveillance events held each year. Reasons for low surveillance system sensitivity include poor sensitivity of the sugar shake method as a diagnostic test for the presence of Varroa in a colony and the relatively low frequency of testing of high-risk colonies in the greater Melbourne area. If the Sugar Shake Team program is to be used as a credible means for Varroa incursion detection the frequency of testing and the number of participants in the program needs to be increased. Research effort should be directed towards identifying more sensitive diagnostic tests to detect the presence of Varroa in honey bee colonies. If Varroa were to be introduced into Australia and there was a need to control the parasite using miticides, the cost per hive per year, if recommended controls were applied, would be in the order of AUD 51 (Q1 40; Q3 65) per hive per year (Chapter 5). In 2020 this represents a 17% reduction in net hive profitability. Assuming colony annual mortality rates attributable to Varroa ranging from 30% to 50% the percentage of apiary-year simulations where the cost of recommended Varroa controls was less than a suboptimal Varroa control strategy ranged from 32% to 43% (assuming a 30% Varroa attributable mortality rate) and 40% to 57% (assuming a 50% Varroa attributable mortality rate). While the use of suboptimal controls may be a pragmatic and rational economic choice for a beekeeper this represents a classic ‘tragedy of the commons’ situation whereby individual users, acting independently according to their own self interest, behave contrary to the common good of the industry. On the basis of these analyses, thought should be given to what changes can be made to the industry to make application of recommended Varroa controls cost effective for beekeepers. The first is to consider ways by which Varroa inspection and treatment times might be reduced. The second is to ensure that the cost of colony replacement is kept relatively high. A model was developed to simulate the introduction and spread of resistant Varroa Sensitive Hygienic (VSH) genetics into the managed honey bee population as a means for enhancing resistance of the feral population (Chapter 6). Introduction of VSH queens into the managed honeybee population had relatively little effect on the development of resistance in the feral population because the spread of Varroa resistance from the managed population to the feral population is slow compared with the rapid collapse of the feral population following Varroa the introduction of the mite. The only exception to this is that if the size of the resistant, managed population is large relative to the size of the feral population. This being the case there is scope for managed honey bee colonies in high risk areas to be seeded with Varroa-resistant queens to form a ‘barrier’ to limit the spread of the mite away from its point of entry into the country. If VSH genetics are to be used in this way as a means for either promoting Varroa resistance in the feral colony population or for iideveloping a Varroa resistance barrier around likely incursion sites (i.e., ports and international airports) it is essential that programs are established well in advance of a Varroa introduction.