Hygienic behaviour selection via freeze-killed honey bee brood not associated with chalkbrood resistance in eastern Australia

Abstract

35 Hygienic behaviour is a social immune response in honey bees shown to help 36 provide resistance to honey bee pests and diseases. A survey of hygienic behaviour 37 and brood diseases was conducted on 649 colonies in eastern Australia to initiate a 38 selective breeding program targeting disease resistance and provide a level of 39 resistance to Varroa (Varroa destructor Anderson and Trueman and V. jacobsoni 40 Oudemans) mites should they become established in Australia. The test population 41 showed a remarkably high baseline level of hygienic behaviour with 17% of colonies 42 meeting or exceeding breeding selection thresholds. Colonies belonging to a 43 breeding program were 5.8 times more likely to be highly hygienic and colonies 44 headed by queens raised from hygienic queen mothers were 2.2 times more likely.45 Nectar availability (nectar yielding flowering plants within honey bee forage range) 46 influenced hygienic behaviour expression but was not a significant predictor of level 47 of hygienic behaviour. Surprisingly, hygienic behaviour was not a significant predictor 48 of the presence of infection of the honey bee brood disease chalkbrood 49 (Ascosphaera apis) and was not influential in predicting severity of chalkbrood the 50 infection in surveyed honey bee colonies. This study, along with reports from 51 commercial beekeepers that chalkbrood infection is on the rise, warrants a deeper 52 exploration of the host-pathogen relationship between Apis mellifera and 53 Ascosphaera apis in Australia. Introduction55 European honey bees (Apis mellifera), are an integral component of food security 56 worldwide. In Australia, honey bees provide essential pollination services for food 57 production, contributing directly to between $8.35 billion and $19.97 billion worth of 3 58 horticultural and agricultural production annually and produce between 20,000 and 59 30,000 tons of honey a year valued at $90 million [1]. Honey bee contribution to 60 Australian food security is only possible because of limited pest and disease 61 exposure as a direct consequence of the country's isolation. Although several major 62 brood diseases are endemic such as, American Foulbrood (Paenibacillus larvae) 63 European Foulbrood (Melissococcus pluton), and chalkbrood (Ascosphaera apis), 64 Australia remains the only country with a significant apicultural industry free of 65 Varroa mites (Varroa destructor Anderson and Trueman and V. jacobsoni 66 Oudemans). 67 V. destructor is the foremost cause of honey bee colony losses globally [2,3], 68 impacting both pollination services and honey production. Varroa parasitism has 69 been shown to vector deadly viruses [4] while chemical treatments used to control 70 Varroa in honey bee hives can affect reproduction [5,6,7] and interact negatively with 71 other agricultural chemicals [8]. Furthermore, Varroa species have been shown to 72 develop resistance to acaricides [9,10] rendering the reliance on these chemicals 73 unsustainable in the long term. 74 Once established, the mite will have devas...