THE PATTERN OF SPREAD OF INVADING SPECIES - 2 LEAF-MINING MOTHS COLONIZING GREAT-BRITAIN

1. Two leaf-mining moths in the genus Phyllonorycter colonized Great Britain in the mid-1980s, both feeding on introduced garden and amenity plants: P. leucographelln on Pyracantha spp., and P. platani on Platanus spp. 2. Systematic surveys of the distribution and spread of the two species were carried out spanning a period of 5 and 3 years. The effect of humans in dispersing the two moths was also studied. 3. The relationship between the square root of the range and time was in both cases remarkably linear, suggesting that the spread of the moths can be viewed as a simple travelling wave. The velocity of this wave was 10.3 km year(-1) for P. leucographella and 8.6 km year(-1) for P. platani. 4. There were slight deviations from the predicted pattern of spread as a series of concentric circles. For P. leucographella these are partially explained by variations in urbanization, which is correlated with the density of host plants. 5. Several foci of colonization outside the main range were detected, due to human activities. There was also evidence of artificial spread in the vicinity of the main advance, but this was not sufficient to obscure the simple pattern detected.