An insect isoscape of UK and Ireland.

Jason Newton

doi:10.1002/rcm.9126

Abstract

The study of insect migration is problematic due to the small size of insects. Stable isotope analysis can be used to elucidate movement, either by geographic assignment of location of a species, or by simply distinguishing migrant from resident populations. There are few isoscapes of any kind in the UK/Ireland available for interrogation. Thus, I have measured stable isotope ratios (of H, C, N and S) of 299 individuals of the non-migratory Brimstone moth (Opisthograptis luteolata) collected from 93 locations around the UK and Ireland by citizen scientists. After removing lipids, stable isotope ratios were measured by continuous flow isotope ratio mass spectrometry, using either a conventional elemental analyser (C, N and S) or a high-temperature, thermal conversion elemental analyser in reductive mode. Maps (isoscapes) were constructed that illustrate the stable isotope spatial distribution of this insect. These are the first isoscapes of H, C, N and S of biological samples covering both UK and Ireland. The insect isoscape patterns can be explained from what we know of moth diet, climate and geology. Sulfur isotopes may be of particular use for distinguishing individuals from areas of unique geology. Isoscape patterns may (with care) predict isotope compositions of other, herbivorous, non-aquatic, chitinous taxa. Such isoscapes, when extended beyond the UK and Ireland, would provide a useful tool to elucidate insect migration.

Highlights

Migration in insects is widespread[1] and in some species exceeds well-known mammalian and avian migrations in terms of biomass.[2]
Size is the main barrier to tracking individual insects over long distances; this is unfortunate, since many insect migrations may be multigenerational where each individual participates in only a section of the migratory circuit
This concurs with other work on non-aquatic fauna whereby the δ2H values of tissue largely reflect the δ2Hp values[36] and, by extension, the δ2H value of wing tissue is largely controlled by latitude, longitude and temperature. δ18O values were not considered given the small amount of material available and that the isoscape would largely mirror that of the δ2H values

Summary

Introduction

Migration in insects is widespread[1] and in some species exceeds well-known mammalian and avian migrations in terms of biomass.[2]. Our understanding of insect migration is surpassed by that of vertebrates because of the small size of insects. Size is the main barrier to tracking individual insects over long distances; this is unfortunate, since many insect migrations may be multigenerational where each individual participates in only a section of the migratory circuit. Extrinsic markers (e.g. tags) require both capture and recapture but this has been popular for insects given the inherent challenges of their small size. The monarch butterfly migration of North America has been extensively studied using numbered adhesive tags.[3] this does require considerable effort since the recovery rate of tagged individuals in such a large population is quite low, 0.046 to 1.27%.4. This does require considerable effort since the recovery rate of tagged individuals in such a large population is quite low, 0.046 to 1.27%.4 Recent technological

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