Quantifying long-range migration in Lepidoptera: integrating population dynamics and flight behaviour

Some common British butterflies (e.g. the Large White and Small White) and moths (e.g. the Silver Y) are known to make long-distance seasonal migrations, sometimes over hundreds of kilometres. These butterflies and moths are pests of agricultural crops in the south of their range (southern Europe), and with climate warming they may migrate to the UK in greater numbers in the future and become important pests. However, we are still far from understanding how these movements are achieved. For example, all earlier observations have made very close to the ground , so we know very little about the heights at which the species generally fly, nor whether the wind at these heights is blowing in the direction that the species are trying to tarvel. Equally, we don't know if the butterflies and moths can control their flight direction when they are flying near the ground if the wind is blowing acros them. We will use two types of radar specially-designed for studying insect migration to investigate whether the butterflies and moths choose to fly at particular times and heights so that they can use winds blowing in a favourable direction to help them migrate in the most advantageous direction. We will also use purpose-built flight simulators, where a tethered insect can choose its flight heading at will, to test whether seasonal factors (such as the hours of daylight) or larval rearing conditions (such as overcrowding or a lack of food) are more important in promoting migratory flight. Finally, we will assess how migration affects the population sizes of the selected species in the UK, and how this is likely to change under the influence of climate change.

Many Lepidoptera have evolved continental-scale migrations to temperate latitudes in order to exploit temporary breeding habitats in which they are unable to over-winter. Given that such movements will become more frequent under climate warming, it is desirable to obtain a better understanding of the mechanisms that underpin them, as this is certain to be needed for integrated pest management strategies in the future. However, we are still far from understanding how these movements are achieved. For example, all earlier observations have been limited to heights within a few 10s of m above the ground, so almost nothing is known about preferred flight-heights, nor whether these are related to favourable winds. Equally, very little is known about how the species influence their displacement directions by means of their flight heading, even when they are flying near the ground. Now, however, the two novel radar techniques that we will employ have removed these constraints, and they thus provide a timely opportunity to characterise the migration syndromes of our target species. We will use our vertical-looking radars to investigate high-altitude flight in relation to meteorological factors, and to monitor temporal fluxes of migration intensity. Flight-paths of species migrating close to the ground will be examined by harmonic radar to determine if they can compensate for lateral wind-drift and thus maintain their preferred flight direction. We will also have access to population data in both the north (UK) and south (Gibraltar) of the species' European ranges. In addition, the role that environmental factors play in promoting migration will be examined using state-of-the-art flight simulators. Taken together these resources represent by far the most powerful suite of observational techniques that have ever been assembled to investigate the population dynamics of insect migrants, and a commensurate level of discoveries into this topic can be expected.