Economic and physical determinants of the global distributions of crop pests and pathogens

Abstract

Crop pests and pathogens pose a significant and growing threat to food security, but their geographical distributions are poorly understood. We present a global analysis of pest and pathogen distributions, to determine the roles of socioeconomic and biophysical factors in determining pest diversity, controlling for variation in observational capacity among countries. Known distributions of 1901 pests and pathogens were obtained from CABI. Linear models were used to partition the variation in pest species per country amongst predictors. Reported pest numbers increased with per capita gross domestic product (GDP), research expenditure and research capacity, and the influence of economics was greater in micro-organisms than in arthropods. Total crop production and crop diversity were the strongest physical predictors of pest numbers per country, but trade and tourism were insignificant once other factors were controlled. Islands reported more pests than mainland countries, but no latitudinal gradient in species richness was evident. Country wealth is likely to be a strong indicator of observational capacity, not just trade flow, as has been interpreted in invasive species studies. If every country had US levels of per capita GDP, then 205 ± 9 additional pests per country would be reported, suggesting that enhanced investment in pest observations will reveal the hidden threat of crop pests and pathogens.

Keywords: biogeography; biological invasions; crop protection; pest management; plant pathology; species distributions.

Figure 1

Observed pest number vs mean crop production 2001–2010. Islands, pink circles; coastal countries, blue squares; landlocked countries, green triangles.

Figure 2

Pests per unit agricultural production vs per capita gross domestic product (GDP). Each point represents a country. Lines show cubic spline smooths to the log-transformed data. Pink circles (solid line), island nations; blue squares (dashed line), coastal nations; green triangles (dotted line), are landlocked nations. Pest numbers are scaled by production to facilitate cross-country comparisons. Islands generally report more pests and pathogens for a given level of production and per capita GDP.

Figure 3

Observed pests vs scientific publications 1996–2012. Islands, pink circles; coastal countries, blue squares; landlocked countries, green triangles.

Figure 4

Effect of economic development on expected pest numbers reported by Myanmar. (a) Expected mean (solid line) and 95% confidence limits (dashed lines) for pest numbers vs per capita gross domestic product (GDP), with the current Myanmar-level investment in research and development (R&D) (0.11% of GDP). (b) Expected mean and 95% confidence limits for pest numbers vs per capita GDP, with US-level investment in R&D (2.64% of GDP). The circle in both panels shows the current reported pest number (351) and per capita GDP (US$904) for Myanmar.

Figure 5

Expected additional number of pests per country. Expected numbers were predicted from the model, in which crop production and crop diversity were held at current levels, but per capita gross domestic product (GDP) and investment in research and development (R&D) were set to current USA levels. Grey shading denotes missing data for that country.