Identification and Risk Assessment for Worldwide Invasion and Spread of Tuta absoluta with a Focus on Sub-Saharan Africa: Implications for Phytosanitary Measures and Management

Abstract

To support management decisions, molecular characterization of data and geo-reference of incidence records of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) were combined with data on the biology and ecology of the pest to estimate its climatic suitability and potential spread at regional and global scale. A CLIMEX model was developed and used for the global prediction of current and future climate-induced changes in the distributional shifts of T. absoluta. Results revealed that temperature and moisture characterized T. absoluta population growth while the pest ability to survive the cold, hot, wet and dry stress conditions are the primary characteristics defining its range frontiers. Simulated irrigation also played an important role in the model optimization. Model predictions suggest that T. absoluta represents an important threat to Africa, Asia, Australia, Northern Europe, New Zealand, Russian Federation and the United States of America (USA). Under climate change context, future predictions on distribution of T. absoluta indicated that the invasive nature of this pest will result in significant crop losses in certain locations whereas some parts of Africa may witness diminution in ranges. The following scenarios may occur: 1) T. absoluta damage potential may upsurge moderately in areas of Africa where the pest currently exists; 2) a range diminution in temperate to Sahel region with moderate upsurge in damage potential; 3) a range expansion in tropical Africa with reasonable upsurge of damage potential. These possible outcomes could be explained by the fact that the continent is already warm, with the average temperature in majority of localities near the threshold temperatures for optimal development and survival of T. absoluta. Outputs from this study should be useful in helping decision-makers in their assessment of site-specific risks of invasion and spread of T. absoluta with a view to developing appropriate surveillance, phytosanitary measures and management strategies.

Fig 1. Phylogenetic tree of T. absoluta samples from Kenya and others obtained from GenBank.

Fig 2. Global known geo-reference location points of T. absoluta.

Point locations in South America correspond to its native distribution, and were obtained from the published literature. Point locations in Africa correspond to survey conducted by the authors of the article.

Fig 3. CLIMEX climatic suitability indices for T. absoluta in South America considered as the native region of the pest.

Predictions are based on the eco-climatic index (EI), a measure of climatic suitability scaled from 1–100, for locations within CLIMEX’s platform station database. EI = (0–5) location is not suitable; EI = (5–20) moderate level of suitability; EI = (20–50) high risk of establishment and EI > 50 very high likelihood of long-term survival. The black dotes are the geo-reference points obtained from literatures.

Fig 4. CLIMEX climatic suitability indices for T. absoluta in Europe.

Predictionsare based on the eco-climatic index (EI), a measure of climatic suitability scaled from 1–100, for locations within CLIMEX’s platform station database. EI = (0–5) location is not suitable; EI = (5–20) moderate level of suitability; EI = (20–50) high risk of establishment and EI > 50 very high likelihood of long-term survival. The black dotes are the geo-reference points obtained from literatures.

Fig 5. CLIMEX climatic suitability indices for T. absoluta in the world.

Predictions are based on the eco-climatic index (EI), a measure of climatic suitability scaled from 1–100, for locations within CLIMEX’s station database. EI = (0–5) location is not suitable; EI = (5–20) moderate level of suitability; EI = (20–50) high risk of establishment and EI > 50 very high likelihood of long-term survival. The black dotes are the geo-reference points obtained from literatures.

Fig 6. CLIMEX climatic suitability indices for T. absoluta at in Africa.

Predictions are based on the eco-climatic index (EI), a measure of climatic suitability scaled from 1–100, for locations within CLIMEX’s station database. EI = (0–5) location is not suitable; EI = (5–20) moderate level of suitability; EI = (20–50) high risk of establishment and EI > 50 very high likelihood of long-term survival. The black dotes are the geo-reference location points obtained from surveys.

Fig 7. CLIMEX climatic suitability indices for T. absoluta in East Africa.

Predictions are based on the eco-climatic index (EI), a measure of climatic suitability scaled from 1–100, for locations within CLIMEX’s station database. EI = (0–5) location is not suitable; EI = (5–20) moderate level of suitability; EI = (20–50) high risk of establishment and EI > 50 very high likelihood of long-term survival. The black dotes are the geo-reference points obtained from surveys.

Fig 8. (A) Potential range shifts in the distribution of T. absoluta in Africa using the eco-climatic indices EI under climate change scenario (a rise of 1.5°C Africa wide temperature and 10% increase of rainfall from March 2—September 30 and 10% decrease in the rest of the year). The map was produced from the difference between the values of EI of the predicted future T. absoluta distribution (obtained when applying climate change criteria) and the distribution of the pest originated from current climate (year 2000) in Africa. EI = 0 demonstrates no range shift; EI < 0 signifies a reduction of climatic suitability EI > 0 represents an increase in the likelihood of survival and permanent establishment of the species. (B) Potential range of increase in number of generations per year of T. absoluta under the selected climate change scenario.