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Predicting the future climate-related prevalence and distribution of crop pests and diseases affecting major food crops in Zambia [1]

['Wilson Nguru', 'The Alliance Of Bioversity International', 'International Center For Tropical Agriculture', 'Ciat', 'Rome', 'Caroline Mwongera']

Date: 2023-01

Environmental factors determine the suitability of natural habitats for crop pests and often facilitate their proliferation and that of the crop diseases they carry. Crop pests and diseases damage food crops, significantly reducing yields for these commodities and threatening food security in developing, predominantly agricultural economies. Given its impact on environmental factors, climate change is an important determinant of crop pest and disease distribution. This study uses Targeting Tools, a climate suitability analysis and mapping toolkit, to explore the potential impact of climate change on select environmental factors linked to crop pest and associated diseases’ proliferation. Based on the existing literature, prediction modeling was performed on 21 key pests and diseases that impact the major food crops for Zambian consumption. Future changes in habitat suitability for these crop pests and diseases were mapped based on their optimal temperature and relative humidity conditions for proliferation. Results project that there will be an overall increased geographical spread of suitable habitats for crop pests (and as follows, crop diseases) that thrive in warmer environments. By the 2030s, crop pests and diseases will increasingly spread across Zambia, with a higher likelihood of occurrence projected under RCPs 2.6, 4.5, and 8.5. Crop pests and diseases that thrive in cooler environments will experience decreasing habitat suitability in the 2030s, but will transition to a slower decrease in the 2050s under RCPs 2.6 and 4.5. Overall crop pest and disease habitat suitability will continue to rise slowly in the 2050s; RCP 8.5 shows an increased habitat suitability for crop pests and diseases that thrive in warm environments, with a decreased likelihood of occurrence for crop pests and diseases that thrive in cooler environments. The results highlight the need for future-facing, long-term climate adaptation and mitigation measures that create less suitable microclimates for crop pests and diseases.

Data Availability: Data for current climate trends (i.e temperature and precipitation) was obtained from Worldclim historical monthly weather data for years 1990 to 2018 ( https://www.worldclim.org/data/monthlywth.html ) Worldclim Citation: Fick, S.E. and R.J. Hijmans, 2017. WorldClim 2: new 1km spatial resolution climate surfaces for global land areas. International Journal of Climatology 37 (12): 4302-4315. Data for the future climate trends was obtained from the CCAFS climate portal - See Direct Link to data ( http://www.ccafs-climate.org/data_spatial_downscaling/ ). CCAFS climate portal citation: Navarro-Racines, C., Tarapues, J., Thornton, P., Jarvis, A., and Ramirez-Villegas, J. 2020. High-resolution and bias-corrected CMIP5 projections for climate change impact assessments. Sci Data 7, 7, doi: 10.1038/s41597-019-0343-8 Base layer for Fig 1 – Fig 10 was obtained from this Geopackage ( https://gadm.org/download_country.html ); The license information can be found here ( https://gadm.org/license.html )-- it states that using the data to create maps for publishing in PLoS (and other journals) of academic research articles is allowed. Additional data used for the generation of mapping results in this article (including Fig 2 ) is provided in the manuscript and in Supporting Information files (includes explicit written permission and signed permission form by copyright owners, and reflected permission on the corresponding figure caption).

Introduction

Crop pests and crop diseases damage food crops and are a major cause of yield losses in agriculture (up to 40% crop loss globally) [1–3]. Climate change has been found to be an important determinant of the abundance, distribution and level of activity of these crop pests and the pest-related diseases they carry [4,5]. According to the Intergovernmental Panel on Climate Change (IPCC), global temperatures have increased by 0.6 ± 0.2°C compared to pre-industrial levels, and are expected to reach a global climate warming of over 1.5–2°C and up to 5.4°C by 2100 [6]. The IPCC also predicts that if temperatures rise by 2°C over the next 100 years, there will be negative effects on living organisms, including crops and livestock [7]. Climatic variability with increased temperature, increased carbon dioxide concentration, changes in precipitation patterns, and extended periods of drought already negatively affect agricultural sectors and exacerbate poverty and food insecurity in developing economies [8,9]. This is especially observed in Sub-Saharan Africa, where agriculture employs more than half of the working population, and drives economic growth [10,11].

Climate change can drastically affect the dynamics of insect pest populations and the diseases they carry [12,13]. These effects are either direct, through the influence of weather conditions on pest physiology and behavior, or indirect, mediated by habitat conditions, host plants, competitors species, and pests’ natural enemies [14]. Indirect effects of climate change on crop pests and diseases also include changes in phenology, distribution, and community composition of ecosystems. In the face of rapid climate-change-related environmental changes, for many species, survival depends on adapting to shifting climates, as these changes can lead to the extinction or the increased proliferation of pest species [15,16].

Insect crop pests are poikilothermic, i.e., cold-blooded organisms, and are highly sensitive to environmental changes [14,17]. For example, many orthopterans—insects often native to warmer regions—have a very limited distribution in higher altitudes and cooler climates. Such crop pests are found in tropical and subtropical regions. The size of the geographical range occupied by a species at any one time is determined by ecological factors including habitat availability, as well as climatic and other environmental parameters [18]. For crop pests to survive, they often adapt to new emerging climate conditions, or create shifts in their geographical distribution to populate more suitable areas [19]. This often leads to an increase in the diversity and abundance of these crop pests and pest-related diseases. Thus, crop pest species that thrive in cooler climates or cooler seasons could be more negatively impacted by global warming as temperatures rise, while species that are adapted to warmer climates like orthopterans could benefit from global warming, with higher altitude areas becoming warmer and more conducive to their survival [20]. Additionally, by altering land use patterns, recent studies have shown that climate change also allows for viral sharing across species that were historically geographically isolated from one another. Thus, the impacts of climate change can lead to zoonotic spillover: cross-species pathogen transmission phenomenon between animals and humans, linking environmental changes and zoonotic disease emergence [16]. Using climatic factors have also been effective predictors for human disease incidence [21–23].

Climate variability has been shown to increase directly transmitted diseases of wildlife [22]. Although zoonotic spillover is primarily a concern for animal and human health, it remains important to consider the potential long-term impacts of climate change on disease emergence stemming from crop pest’ and related diseases’ distribution. In fact, zoonoses can be facilitated by multiple host taxa; historically, at least 5 zoonoses have been attributed to the order of Dipterans [24], which includes common crop pest species like the rice gall midge. This further highlights a need to better predict potential crop pest distribution.

The observed climate change-related rise of global temperatures alters two important, agriculturally relevant characteristics of insect pests: their metabolic rates, and the length of their life cycles. On one hand, individual insects’ metabolic rates increase with temperature, and in turn, so do their growth and food consumption rates, leading to increased rates of crop destruction by said pests [25,26]. On the other hand, insect crop pest populations change as their growth rates vary with temperature. For instance, increases in mean annual temperatures result in some crop pest species growing faster, and completing their life cycles two to three weeks early [27]. The resulting shortened life cycles often lead to rapid population growth with an increased abundance of crop pests and pest-related diseases, and more destructive effects on crops [13,28]. This can be observed particularly in temperate regions and high-altitude areas. The global increase in temperatures will likely cause 10–25% yield losses from crop pests [12].

Climate change also impacts crop pests through changing precipitation patterns. For instance, climate change-related decreases in precipitations can lead to the extinction of some species of crop insect pests for lack of adequate water resources, and to the growth of other species that are more adapted to low humidity such as aphids [29]. Alternatively, increasing average precipitation and rainfall intensity can also facilitate or impede proliferation of certain species of crop pests and pathogens [30–32]. Such extreme events can in some cases disrupt both natural and implemented biocontrol methods, namely by impacting the growth and proliferation of biological control agents and their host targets [33]. In other instances, warmer environmental conditions stemming from climate change may increase the effectiveness of many natural enemy species of said crop pests, making them more vulnerable to control measures [34]. The extinction of crop pest natural enemy species can also occur as a result of changing precipitation patterns, leading to increased crop pest proliferation.

The occurrence, prevalence, and severity of crop diseases are impacted by climate change [35], which have numerous implications for how diseases and crops interact. The time, preference, and effectiveness of using chemical, physical, and biological control techniques, and their application within integrated pest management (IPM) strategies can also be impacted by climate change factors, which have an impact on both the host and the pathogen [36]. For instance, some temperature patterns can encourage pathogen growth or increase host resistance to pathogenic diseases. This is seen in wheat and oats, which become more susceptible to rust diseases with increased temperature, while other forage species become less susceptible to these diseases under the same conditions [37]. Furthermore, temperature changes may lead to certain pests going through between 1 and 5 additional lifecycles per season, increasing their associated pathogens’ capacity to overcome plant resistance [38].

Warmer, wetter weather, and higher CO 2 levels are favorable conditions for the growth of many weeds, crop pests, and fungi [39,40]. High CO 2 concentrations may result in slower plant decomposition rates, which can raise fungal inoculum levels and aid the development of more fungal spores [39]; alternatively, elevated CO 2 levels can alter the physiological makeup of crops and increase their resistance to some crop diseases. Thus, crop fungal diseases threaten crops in areas where climate-related environmental changes can be observed [29], potentially exacerbating issues related to pest-transmitted crop diseases.

These climate change impacts on crop pests and crop diseases bring about major implications for crop production and food security, particularly in developing countries like Zambia where the need to increase and sustain food production is urgent. While many studies have investigated the isolated impacts of climate change factors on crop pests and diseases [33,41–44]; a notable gap in the available literature is the absence of an approach that assesses interacting environmental factors that are conducive to crop pests proliferation in specific contexts (e.g. agroecology), and analyzes these environmental factors’ impacts on crop pests’ habitats.

To help predict climate change impacts and plan for mitigation efforts, the IPCC 5th assessment report adopted four potential pathways to describe a range of probable climate futures that can be expected in the coming decades [45]. These pathways, known as the Representative Concentration Pathways (RCPs), capture assumptions regarding future temperature increases due to carbon concentration and radiative forcing. This collection of predictive greenhouse gas (GHG) concentration and emissions pathways (or scenarios) were created to support research on the impacts of climate change and associated policy responses [46]. They include RCPs 2.6, 4.5, 6.0, and 8.5, which cover a spectrum of more to less optimistic climate change outcomes. The different climate futures projected in the RCPs are all considered likely, based on the volume of greenhouse gases expected to be emitted in the near future, and can be used to define predictive modeling parameters [47].

The negative global impacts stemming from the spread of the Coronavirus during the COVID-19 pandemic highlighted the importance of assessing the role of environmental drivers in explaining pathogen proliferation to forecast future outbreak risks. Agriculture is one of the sectors most exposed to climate change and to the impacts of crop pests and crop diseases; it is hence increasingly important to accurately predict the future distribution of these harmful agents to enhance preparedness measures and mitigate crop losses due to climate change-related pest infestations. In this study, we combine global studies and a habitat suitability analysis and mapping tool (Targeting Tools) to develop an approach linking habitat suitability for crop pests and crop diseases to their proliferation patterns. We also infer some impacts of crop pests and crop disease proliferation on local food security under a spectrum of climate change scenarios. This approach will contribute to the development of recommendations that support forward-facing climate adaptation in vulnerable areas, with a strong focus on measures to mitigate the potential future climate change effects on crop pest and crop disease distribution in Zambia.

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[1] Url: https://journals.plos.org/climate/article?id=10.1371/journal.pclm.0000064

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