Pests on the move

Going hungry: The Irish Famine of the 1840s may appear a distant memory, but new strains of the pathogen that triggered it are still emerging and threatening food security. The image shows the Famine Monument at Dublin. (Photo: Professor Colin R. Howard (http://www.colinhoward.co.uk/photography.htm).) A simple line graph can tell a story of unimaginable tragedies. The population of Ireland increased steadily to reach just over eight million in 1848, then dropped to below six million by 1860. It took a century to return to growth but hasn’t recovered to this day. What happened between these two dates was that the island largely living from potato farming was hit by an outbreak of the late blight, a potato disease caused by the oomycete Phytophthora infestans. (Oomycetes or water moulds are a group of single-cell organisms originally described as fungi, but now classified as protists.) The total loss of the island’s main crop, combined with equally catastrophic mismanagement from the ‘absentee landlords’ and the epidemics sweeping through the starved population, left more than one million Irish people dead. The remainder of the population loss was due to emigration, mainly to North America, which is now home to many more people of Irish descent than their home island. We would like to think that such events belong to a dark and distant past. It happened just before photography became available to document world events, so we only have sketchy drawings, a few monuments and literary impressions like Liam O’Flaherty’s novel Famine as reminders of the tragedy. However, dangerous plant diseases are still around, and human activities such as globalised trade, large-scale farming and climate change provide new opportunities for pests to wreak havoc.