Varroa Appears to Drive Persistent Increases in New Zealand Colony Losses

SIMPLE SUMMARY: New Zealand is a significant exporter of high-value honey, and honey bees are the major pollinator of many important food crops. Bee colonies naturally die over winter due to the pressures of the season, and we have been surveying beekeepers annually since 2015 to record these losses. The percentage of colonies that died over winter increased every year between 2015 and 2021. While problems with queen bees were previously the main issue to which beekeepers attributed losses, 2021 was the first year in which beekeepers identified the parasitic varroa mite as the main cause. The mite invaded New Zealand in 2000; despite being in the country for more than 20 years, New Zealand beekeepers are still struggling to control varroa. ABSTRACT: New Zealand’s temperate climate and bountiful flora are well suited to managed honey bees, and its geographic isolation and strict biosecurity laws have made sure that some pests and diseases affecting bees elsewhere are not present. Nevertheless, given the importance of pollination and high-value export honey to the economy, New Zealand began systematically measuring winter colony losses in 2015. The New Zealand Colony Loss Survey is modelled on the COLOSS survey but has been adapted to the New Zealand apicultural context. Some 49% of New Zealand beekeepers completed the winter 2021 survey. Between 2015 and 2021, overall colony loss rates increased monotonically from 8.37% [95% CI: 7.66%, 9.15%] to 13.59% [95% CI: 13.21%, 13.99%]. Whereas beekeepers most commonly attributed losses to queen problems between 2015 and 2020, attributions to varroa have escalated year-on-year to become the largest attributed cause of colony loss. Losses to varroa are perhaps amplified by the 23.4% of respondents who did not monitor mite loads and the 4.4% of beekeepers who did not treat varroa during the 2020/21 season. Indeed, most beekeepers consider their treatment to be effective and note that treating at the wrong time and reinvasion were major drivers of losses to varroa.