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University of New South Wales (UNSW) 2016

Testing ideas about Australian insect migration using entomological radar observations and a regional scale meteorological model

Hao, Zhenhua

Titre : Testing ideas about Australian insect migration using entomological radar observations and a regional scale meteorological model

Auteur : Hao, Zhenhua

Université de soutenance : University of New South Wales (UNSW)

Grade : Doctor of Philosophy (PhD) 2016

Résumé
The primary objective of the present study has been to investigate the migratory flight characteristics of Australian insects and the influence of weather conditions on their migrations. The primary data were observations from an insect-monitoring radar (IMR) operated at Bourke (30.0392° S, 145.952° E, 107 m above MSL), NSW, Australia. The IMR provided direct measurements of the insects’ flight and an indication of their identities. Different species groups, such as Australian plague locusts Chortoicetes terminifera (Walker), large moths, medium moths and small insects were selected according to their size, shape and wing-beat frequency. A high-resolution numerical atmospheric model, TAPM Version 4, was used to estimate wind speed and direction at the radar site for the heights at which the insects were flying. A verification exercise demonstrated that root-mean-square errors for TAPM wind speeds were significantly smaller than typical insect flight speeds. Combining radar data and TAPM winds has enabled the identification of differences in flight behaviour between species groups and from season to season, including peak months, peak migration heights, airspeeds, temperature preferences, choices of wind direction and speed, and frequency of orientation. In addition, the utility of surface temperature and wind speed for forecasting locust migration events was assessed, with predictions proving effective in spring and autumn but not in summer. An investigation of insect heading directions showed that the migrants were sometimes carried backwards by the wind and that their headings changed with changing wind direction and showed a strong bias towards the right of the wind direction. This is consistent with proposals that orientation arises through a response to wind shear and turbulence but the bias direction is contrary to expectations from findings in the Northern Hemisphere ; however, it can be understood as a response to turbulence arising from the thermal wind instead of the Ekman spiral. Finally, the applicability to insect migration of analysis methods developed for determining whether migrating birds compensate for side winds or experience drift has been investigated. A number of difficulties were identified, but by partitioning the data it was shown that locusts undergo full or partial drift during spring.

Mots clés : meteorological model ; insect migration ; insect-monitoring radar

Présentation

Page publiée le 14 juillet 2017