ABSTRACT
After abnormal weather events, there is often a rapid upsurge in pests and diseases with the potential to threaten human food security. An outbreak of potato blight disease (Phytophora infestans) in mid-nineteenth-century Ireland was triggered by unusually warm and wet weather in 1845. This led to at least 1.5 million famine-related
deaths over the following three years and the emigration of about 1 million people. Like most organisms, pests produce more offspring than are required for replacement of the adults when they die, and the stability of populations is maintained through high juvenile mortality. If the environ - mental factors controlling juvenile mortality are eased, many species have the capacity to attain plague proportions. This is most likely to occur in arid and semi-arid areas that can be transformed by rains.
