Australian Bogong moths Agrotis infusa (Lepidoptera: Noctuidae), 1951–2020: decline and crash

Abstract

The Bogong moth Agrotis infusa is well known for its remarkable long‐distance migration – a return journey from the plains of southeast Australia to the Australian Alps – as well as for its cultural significance for Indigenous Australians. Each spring, as many as four billion moths are estimated to arrive in the Australian Alps to aestivate in cool mountain caves and in boulder fields, bringing with them a massive annual influx of energy and nutrients critical for the health of the alpine ecosystem. However, a massive decline in moths present at their aestivation sites has occurred over the past 3 years, with only a few individuals present where hundreds of thousands could earlier be found. In order to understand the possible sources of decline, we analysed historical records of Bogong moth numbers at aestivation sites in the Australian Alps, including observations on Mt. Gingera (NSW) in the early 1950s, observations from 1980 onwards in the Snowy Mountains (NSW) and an almost‐unbroken series of observations each summer over the past 53 years in three caves at different elevations on Mt. Buffalo (Victoria). This analysis shows that moth numbers were probably steady from 1951 until about 1980, fluctuated and slowly fell from then until 2016 and dramatically crashed in 2017. In the Murray–Darling Basin, the main winter breeding ground of Bogong moths, changes in farming practices, such as increasing land clearing for crops (which has removed around a quarter of a billion moths annually from the mountains compared to pre‐European levels), has probably driven some of the decline in Bogong moth numbers observed from 1980 to 2016. The impact of insecticide remains unclear and is in urgent need of further study. Even though we found little evidence that increasing global temperatures per se are responsible for the Bogong moth decline, the Australian climate has nonetheless become drier and warmer over past decades, possibly hampering the survival of immature stages in the breeding areas and confining adult aestivation to gradually higher elevations. The crash in moth numbers from 2017 is most likely due to the recent severe drought in the moth's breeding grounds.

Camera-based monitoring of Bogong moths in Alpine Australia reveals drivers of migratory behaviour

“…As well as being interesting in its own right, the answer to this question is rapidly becoming critical to the conservation of the unique Australian Alpine ecosystem, which accommodates many species that rely on the annual influx of nutrients brought by the Bogong moth migration (Gibson et al, 2018; Green, 2011, 2003). Concerningly, an estimated 200-fold reduction in the Bogong moth population was observed between the 2016–2017 and 2017–2018 summers, following a slow, but consistent decline since the early 1980s (Green et al, 2021; Mansergh et al, 2019). This has led to the recent listing of the Bogong moth as endangered on the IUCN Red List (Warrant et al, 2021).…”

“…However, reliable monitoring of Bogong moths in their breeding grounds remains an unsolved challenge (Wintle et al, 2021). At the end of their spring migration, a number of methods have been used to monitor Bogong moths close to their aestivation sites, including light trapping (Gibson et al, 2018; Wintle et al, 2021), light beam surveys, (Monk, 2021), aestivation site surveys (Caley and Welvaert, 2018; Green et al, 2021), ski surveys of Bogong moth carcasses on the snow (Green et al, 2021), and fox scat surveys (Green, 2010; Green and Osborne, 1981). Each of these methods have their idiosyncrasies, and are to varying degrees laborious, limiting their utility for large-scale long-term monitoring programs, such as the 100-site Bogong moth monitoring program recommended by Wintle et al (2021).…”

Inexpensive monitoring of flying insect activity and abundance using wildlife cameras

“…The Bogong moth is an important source of energy and nutrients in the fragile Australian alpine ecosystem (Green, 2011), and is a model species for studying directed nocturnal insect migration and navigation (Adden et al, 2020; Dreyer et al, 2018; Warrant et al, 2016). A dramatic drop in the population of Bogong moths has been observed in recent years (Green et al, 2021; Mansergh et al, 2019), adding it to the growing list of known invertebrate species whose populations are declining (Sánchez-Bayo & Wyckhuys, 2019). The present method will prove invaluable for ongoing efforts to understand the behaviour and ecology, and monitor the population of this iconic species.…”

Large-scale whole-genome sequencing of migratory Bogong moths Agrotis infusa reveals genetic variants associated with migratory direction in a panmictic population

“…This indicates that the Bogong moth population has likely recently recovered from a past genetic bottleneck, resulting in variation being dominated by mutations rather than genetic-drift-mediated partial fixation. It is known that Bogong moth population size can vary dramatically from year to year (Green et al, 2021), although it is thought that this has been underpinned by a slow downward trend over the last half-century ( ibid . ).…”

“…ACT = Australian Capital Territory. Adapted from Green et al (2021). Inset, upper left: The Australian Bogong moth Agrotis infusa (Boisduval, 1832).…”