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Wild rabbits in Australia developed genetic resistance to the myxoma virus, which was introduced as a biological control agent. However, little is known about the rate at which this evolutionary change occurred. We collated data from challenge trials that estimated rabbit resistance to myxomatosis in Australia and expressed resistance on a continuous scale, enabling trends in its development to be assessed over 45 years up to 1995. Resistance initially increased rapidly, followed by a plateau lasting ten years, before a second rapid increase occurred associated with the introduction of European rabbit fleas as myxoma virus vectors. By contrast, in the United Kingdom, where rabbit flea vectors were already present when the myxoma virus initially spread, resistance developed more slowly. No estimates of rabbit resistance to myxomatosis have been made for almost 30 years, despite other highly lethal rabbit pathogens becoming established worldwide. Continued testing of wild-caught rabbits in Australia to determine current levels of resistance to myxomatosis is recommended to assess its current effectiveness for managing pest rabbits. Given the economic and environmental significance of invasive rabbits, it would be remiss to manage such biological resources and ecosystem services poorly. [ABSTRACT FROM AUTHOR]

European rabbit fleas were released among Australian wild rabbits in the late 1960s to supplement mosquitoes as vectors of myxoma virus. Data from study sites across southern Australia in the 1960s and 1970s are reviewed to discern common elements of flea-borne myxomatosis epizootics and a simple model is proposed to explain how virus virulence and food quality interact to determine rabbit abundance. Low, stable populations of rabbits implied that, despite virus attenuation and increased rabbit disease resistance, flea-borne myxomatosis was extremely important in controlling rabbit populations. Despite the enhancement of myxomatosis, livestock producers benefitted little from the additional pasture because marketing difficulties were not conducive to industry growth. Native wildlife likely benefitted, nonetheless. European rabbit fleas, Spilopsyllus cuniculi (Dale), enhanced myxomatosis as a biological control agent in Australia. They spread myxoma virus among young rabbits in early spring, causing extremely high mortality, reducing grazing pressure, increasing the availability of pasture vegetation in early summer. New insights into the interactions between virus virulence and food quality that determine rabbit abundance are provided. Photograph from 'Distribution of British Fleas' (https://britishfleas.myspecies.info/). [ABSTRACT FROM AUTHOR]