Cyril Piou’s research while affiliated with Institut Agro Dijon and other places

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Publications (107)


Environmental factors associated to breeding areas of the South American locust Schistocerca cancellata on a regional scale
  • Article

August 2024

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15 Reads

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1 Citation

Austral Ecology

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Cyril Piou

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Locusts are globally recognized as major pest threats. In the first half of the 20th century, the South American locust caused great economic losses. After the implementation of preventive management, large‐scale upsurges ceased. In 2015, resurgence of S. cancellata led to swarms affecting northern Argentina, Paraguay, and Bolivia, prompting control agencies to address an almost forgotten problem. After six decades without a major locust outbreak, there were limited and outdated studies on this species. This study aims to identify key environmental factors associated with the spatial distribution of S. cancellata oviposition sites. We focus on explanatory variables that represent physical and chemical properties of soil and vegetation cover. To understand the relationships between each potential explanatory variable and the presence‐absence of S. cancellata oviposition sites, we first performed regression analyses applying a linear and quadratic structure for each explanatory variable. Then, we performed comparisons of logistic regression models in a multi‐model inference framework, where CAIC and weights of evidence were analysed. Our results show that the South American locusts chose to lay their eggs in areas with a low proportion of natural forest and flooded grasslands and a high proportion of non‐vegetated areas, where the soils are flat, with neutral pH, and low salinity. We also determined that an increase in the proportion of cultivated areas is associated with an increase in the probability of breeding presence of this species. The locust's habitat falls within the Dry Chaco, a global deforestation hotspot, evidencing a rapid replacing of forests for plantations. Since both the diminish of forest and the increase in cultivated areas are associated with an increase in oviposition sites, we consider that breeding areas will likely increase. The results found herein can be used to map the potential breeding habitats to help preventive management against the South American locust.


Conceptual diagram of main processes simulated in the BOOSTIT model. Dotted rectangle: immature stages of fruit flies. Dashed rectangle: adult flies. Bold rectangle: released sterile flies. The colours represent the entities involved in the processes: The fly's processes are in brown and the landscape cell's ones are in green. Grey arrows: demographic parameters. Bold arrows: interactions between sterile and wild flies. Dotted arrows: interactions between flies and the environment.
Proportion of mango fruits saved by the boosted SIT according to the day of first release (x axis), number of releases (columns), release interval (box shade), and the sterile/wild ratio (rows).
Proportion of saved fruits under the best boosted SIT and SIT scenarios. Best boosted SIT corresponds to the parameter value combination that allowed the best fruit protection in the boosted SIT scenario (rt = 91, rn = 7, ri = 15, swr = 10, see Fig. 2). Best SIT corresponds to the parameter value combination that allowed the best fruit protection in the SIT scenario (rt = 91, rn = 7, ri = 15, swr = 10; see Appendix, Fig. A1).
Benefit/cost ratio (BCR) of the parameter combination that gave (on the right) the best fruit protection under boosted SIT and SIT (with rt = 91, rn = 7, ri = 15, swr = 10) and (on the left) the best BCR under boosted SIT and SIT (with rt = 152 and 121, respectively, rn = 3, ri = 15, swr = 1).
The number of fruit protected by the SIT according to the start of releases, the release intervals, the number of releases and the sterile/wild male ratio (S/W).

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Exploration of the potential of a boosted sterile insect technique to control fruit flies in mango orchards
  • Article
  • Full-text available

June 2024

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51 Reads

BACKGROUND An innovative version of the sterile insect technique (SIT) for pest control, called boosted SIT, relies on the use of sterile males coated with a biocide to control a target wild pest population of the same species. The objective of the present study was to assess the relevance of such technology to control the fruit fly Bactrocera dorsalis and fruit losses in mango orchards using. An agent‐based simulation model named BOOSTIT was used to explore the reduction of fruit losses thank to sterile male fruit flies control and economic benefits according to different strategies of sterile male release. The simulation considered a landscape of 30.25 ha made up of four mango orchards. RESULTS The SIT and the boosted SIT reduced fruit losses when releases were made before the mango fruiting period. According to model simulations, releases should be performed at least seven times at 2‐week intervals and with a sterile/wild male ratio of at least 10:1. Considering the benefit/cost ratio (BCR), few releases should be done with a late start date. The BCR showed economic gains from the two control methods, the number of saved fruits and BCR being higher for SIT. CONCLUSION Our simulations showed that SIT would have better results than the boosted SIT to contribute to an effective control of Bactrocera dorsalis at the scale of a small landscape. We highlight the need for laboratory studies of other types of pathogen to find a suitable one with higher incubation time and lower cost. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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Global perspectives and transdisciplinary opportunities for locust and grasshopper pest management and research

May 2024

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167 Reads

Journal of Orthoptera Research

Locusts and other migratory grasshoppers are transboundary pests. Monitoring and control, therefore, involve a complex system made up of social, ecological, and technological factors. Researchers and those involved in active management are calling for more integration between these siloed but often interrelated sectors. In this paper, we bring together 38 coauthors from six continents and 34 unique organizations, representing much of the social-ecological-technological system (SETS) related to grasshopper and locust management and research around the globe, to introduce current topics of interest and review recent advancements. Together, the paper explores the relationships, strengths, and weaknesses of the organizations responsible for the management of major locust-affected regions. The authors cover topics spanning humanities, social science, and the history of locust biological research and offer insights and approaches for the future of collaborative sustainable locust management. These perspectives will help support sustainable locust management, which still faces immense challenges such as fluctuations in funding, focus, isolated agendas, trust, communication, transparency, pesticide use, and environmental and human health standards. Arizona State University launched the Global Locust Initiative (GLI) in 2018 as a response to some of these challenges. The GLI welcomes individuals with interests in locusts and grasshoppers, transboundary pests, integrated pest management, landscape-level processes, food security, and/or cross-sectoral initiatives.


Quantitative analysis of behavioural phase difference in Locusta migratoria migratorioides (Reiche & Fairmaire, 1849) (Orthoptera, Acrididae) from the examination of spatial distribution patterns

April 2024

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34 Reads

International Journal of Tropical Insect Science

The field of animal behaviour has often relied on tracking and recording the behaviour of a single individual. For example, for decades, gregarious locust behaviour research has used a standard assay that tracks the path of an individual in a cell, including how much time it spends next to an adjacent cell containing a group of stimulus locusts. However, this process can be time-consuming and impractical in lab and field settings. Here, we validate a complementary approach that uses spatial distribution patterns of a group of locusts in a circular arena to characterize the level of gregarious behaviour. We examined temporal variations in nearest neighbour distances as a criterion of attraction-repulsion and the successive changes of position of the individuals as a criterion of activity level. We used 3rd instar juveniles of the Migratory Locust, Locusta migratoria migratorioides (Reiche and Fairmaire1849), reared in isolated or crowded conditions. Locusts exhibit density-dependent plasticity, and crowd-rearing induces gregarious behaviour. As predicted, we found a larger nearest-neighbour distance between isolated-reared hoppers (indicating repulsion) than mass reared hoppers, which showed attraction to their conspecifics. Mass reared locusts walked greater distances, marking higher activity levels, which is another characteristic of gregarious locusts. These results indicate that this is an efficient and effective method of quantifying gregarious behaviour.


An increase in management actions has compensated for past climate change effects on desert locust gregarization in western Africa

April 2024

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43 Reads

Heliyon

In response to high population density, the desert locust, Schistocerca gregaria, becomes gregarious and forms swarms that can cause significant damage to crops and pastures, threatening food security of human populations from western Africa to India. This switch from solitary to gregarious populations is highly dependent on favorable weather conditions. Climate change, which has been hypothesized to shift conditions towards increasing risks of gregarization, is therefore likely to have significant impacts on the spatial distribution and likelihood of outbreak events. However, the desert locust is intensely managed at large scales, which possibly counteracts any increased risk of outbreaks due to a more favorable climate. Consequently, understanding the changes in risks in the future involves teasing out the effects of climate change and management actions. Here we studied the dynamics of gregarization at the very early stages of potential outbreaks, in parallel with trends in climate and management, between 1985 and 2018 in western Africa. We used three different spatial scales, with the goal to have a better understanding of the potential effects of climate change per se while controlling for management. Our first approach was to look at a regional scale, where we observed an overall decrease in gregarization events. However, this scale includes very heterogeneous environments and management efforts. To consider this heterogeneity, we divided the area into a grid of 0.5° cells. For each cell, a climate analysis was performed for rainfall and temperature, with trends obtained by a harmonic decomposition model on monthly data. Analyses of gregarization showed only a few significant trends, both positive and negative, mainly found in western Mauritania where management effort has increased. To improve the statistical power, these cells were then grouped into larger homogeneous climatic clusters, i.e. groups of cells with similar climatic conditions and similar climatic trends over the study period. At this scale, gregarization events depend on the intersection between climate conditions and management efforts. The clusters where gregarization increased were also the ones with the highest increase of management. These results highlight the important effect of preventive management, which may counteract the positive effects of climate change on locust proliferation.


Towards reusable building blocks for agent-based modelling and theory development

March 2024

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330 Reads

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7 Citations

Environmental Modelling & Software

Despite the increasing use of standards for documenting and testing agent-based models (ABMs) and sharing of open access code, most ABMs are still developed from scratch. This is not only inefficient, but also leads to ad hoc and often inconsistent implementations of the same theories in computational code and delays progress in the exploration of the functioning of complex social-ecological systems (SES). We argue that reusable building blocks (RBBs) known from professional software development can mitigate these issues. An RBB is a submodel that represents a particular mechanism or process that is relevant across many ABMs in an application domain, such as plant competition in vegetation models, or reinforcement learning in a behavioural model. RBBs need to be distinguished from modules, which represent entire subsystems and include more than one mechanism and process. While linking modules faces the same challenges as integrating different models in general, RBBs are “atomic” enough to be more easily re-used in different contexts. We describe and provide examples from different domains for how and why building blocks are used in software development, and the benefits of doing so for the ABM community and to individual modellers. We propose a template to guide the development and publication of RBBs and provide example RBBs that use this template. Most importantly, we propose and initiate a strategy for community-based development, sharing and use of RBBs. Individual modellers can have a much greater impact in their field with an RBB than with a single paper, while the community will benefit from increased coherence, facilitating the development of theory for both the behaviour of agents and the systems they form. We invite peers to upload and share their RBBs via our website - preferably referenced by a DOI (digital object identifier obtained e.g. via Zenodo). After a critical mass of candidate RBBs has accumulated, feedback and discussion can take place and both the template and the scope of the envisioned platform can be improved.


Upwind flight partially explains the migratory routes of locust swarms

January 2024

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53 Reads

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2 Citations

Ecological Modelling

To be efficient, locust swarm control must focus on the place where eggs are laid and hopper bands may appear. But swarms travel a lot and among all the places likely to host them, there is a need to predict to which exactly they will fly. It is then essential to consider movement dynamics to anticipate any displacement that may lead to a further reproduction of locust swarms. Swarms mostly fly downwind and sometimes upwind. We designed an agent-based model to explore swarm displacements depending on the direction of the wind and the possibility for the swarms to realise upwind flights. A primary objective was to assess how upwind flights can improve the replication-and prediction-of documented migratory paths. We looked at the effects of using upwind flight on the swarm ratio arriving in expected (i.e. historically known) areas. Our simulations clearly showed that using upwind flight helped for a better replication of Schistocerca gregaria migrations than not using upwind flight. Not using upwind flight reduced swarm dispersion and reduced the range of migrations. Hence, prevailing winds alone cannot explain locust swarm migrations. Food intake must also be considered to regulate movement dynamics and vegetated areas seem to be more attractive to locusts than expected. Our simulations did not perfectly reproduce the general patterns of migrations in some scenarios, but this invites further investigations and the use of other types of field data to calibrate the model. Nonetheless, our results highlighted the importance of upwind flight and showed the major role of wind and temperature on swarm displacement.



A theoretical framework for upscaling species distribution models

September 2023

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380 Reads

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1 Citation

Species distribution models (SDM) have become one of the most popular predictive tools in ecology. With the advent of new computation and remote sensing technology, high‐resolution environmental data sets are becoming more and more common predictors in these modelling efforts. Understanding how scaling affects their outputs is therefore fundamental to understand their applicability. Here, we develop a theoretical basis to understand the consequences of aggregating occurrence and environmental data at different resolutions. We provide a theoretical framework, along with numerical simulations and a real‐world case study, to show how these scaling rules influence predictive outputs. We show that the properties of the environment–occurrence relationships change when the data are aggregated: the mean probability of occurrence and species prevalence increases, the optimal environmental values shift and classification rates increase at coarser resolutions up to a certain level. Furthermore, and contrary to the widespread expectation that high‐resolution data would produce better predictions, we show here that model performance may increase using coarser resolution data sets rather than the inverse. Finally, we also show that model performance depends not only on the environment–occurrence relationship but also on the interaction between this and the geography and distribution of the available environment. This theoretical framework helps understanding previously incoherent results regarding SDM upscaling and model performance, and illustrates how theoretical and empirical results can provide important feedbacks to advance in understanding scaling issues in macroecology. The interaction between the shape of the environment–occurrence relationship and the rates of change of the environment is fundamental to understand the effects of upscaling in model performance, and may explain why some models are more difficult to transfer to different regions. Most importantly, we argue that there are conceptual choices related to scaling and SDM fitting that require expert knowledge and further explorations between theory and practice in macroecology.


How molting locusts avoid cannibalism

April 2023

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107 Reads

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3 Citations

Behavioral Ecology

Group living has various benefits, but it also carries costs, such as risk of cannibalism. Molting is a vulnerable period of being cannibalized in juvenile arthropods, but how gregarious arthropods avoid this threat is poorly understood. Here, we examined how actively migrating gregarious nymphs of desert locust, Schistocerca gregaria, avoid cannibalism during molting, in the Sahara Desert of Mauritania. In the field, gregarious nymphs cyclically march and feed on grass during the day. Our field observations found that marching behavior helped separating pre-molting and cannibalistic non-molting nymphs. Cannibalistic non-molting nymphs marched away from roost plants, leaving sedentary pre-molting nymphs behind, creating cannibal-free spaces. Some non-molting nymphs reached a pre-molting state after daytime marching, thus both pre- and non-molting nymphs roosted on same plants at night. However, pre-molting nymphs moved away from conspecifics prior to molting. Starvation experiments confirmed that food-satiation decreased cannibalistic necrophagy. Physiological surveys of diel feeding and molting patterns revealed that nymphs molted at times when conspecifics were food-satiated rather than hungry. Hence, our results indicate that behavioral and physiological traits of gregarious locusts could function to spatiotemporally separate molting locusts from cannibalistic conspecifics, thus reducing molting-associated cannibalism. This is the first report of migration-dependent molting synchrony as a mechanism reducing costs of aggregation in gregarious arthropods.


Citations (64)


... Accurate forecasting depends on a relatively clear understanding of the population dynamics of the species concerned, and research on these aspects needs to continue leading to improved models and forecasting, especially in the face of the effects of man-made alterations to the environment. Recent studies have shown that land clearing for agriculture has provided a much larger area suitable for the South American locust [73], while for the Australian plague locust, there are suggestions that climate change may reduce outbreaks in the near future [74]. In such potentially changed circumstances, research is essential to ensure the continued accurate forecasting needed for early intervention preventive management, and such studies should integrate the latest techniques of artificial intelligence and machine learning algorithms. ...

Reference:

World’s Best Practice Locust and Grasshopper Management: Accurate Forecasting and Early Intervention Treatments Using Reduced Chemical Pesticide
Environmental factors associated to breeding areas of the South American locust Schistocerca cancellata on a regional scale
  • Citing Article
  • August 2024

Austral Ecology

... This includes, for example, keeping modelling notebooks (Ayllón et al. 2021) or protocols for ensuring simulation validity (Troost et al. 2024). In addition, the concept of reusable building blocks has been suggested (Berger et al. 2024). These building blocks are components of an agent-based model that represent specific mechanisms or processes relevant across different modelling contexts. ...

Towards reusable building blocks for agent-based modelling and theory development

Environmental Modelling & Software

... In this scenario, as observed in Lucknow, swarm movements were predominantly aligned with the broader-scale (25 km) wind patterns, with minimal deviation, generally following the downwind direction. Nonetheless, wind alone may not be an exclusive factor influencing their flight path (Sorel et al., 2024). Multiple other factors, including humidity, temperature or food availability, may influence flight patterns. ...

Upwind flight partially explains the migratory routes of locust swarms

Ecological Modelling

... Upscaling methods (e.g. spatial thinning) can help match fine-grain response data with coarse-grain environmental data (Steen et al. 2021, Meynard et al. 2023. However, in cases where the ecological grain is finer than the covariate grain, upscaling induces information loss in finegrain variability (McInerny and Purves 2011). ...

A theoretical framework for upscaling species distribution models

... Nevertheless, in many of the articles, categorization came much earlier on in the data processing stage or during data collection (and thus the publication was assigned as 'no' for categorization in our review or was not included if continuous predictor variables were absent in the final model). For example, one study used a 10 cm cut-off to categorize whether a conspecific was 'near' versus 'far' during data collection and near/far were used as a categorical predictor variable [12]. This article was not assigned a 'yes' for categorization because categorization was done during the data collection phase. ...

How molting locusts avoid cannibalism
  • Citing Article
  • April 2023

Behavioral Ecology

... armed conflicts, climatic emergencies), the capacity of the management teams to respond to urgent needs (e.g. lack of personnel and economic constraints), or lack of knowledge regarding future weather conditions, may lead to delayed or imprecise forecasts [39]. Therefore, even though management efforts have increased overall, they remain very heterogeneous both spatially and temporally. ...

Spatiotemporal risk forecasting to improve locust management
  • Citing Article
  • March 2023

Current Opinion in Insect Science

... Demo-genetic Agent Based Models (DG-ABMs), defined as "individual-based (meta) population dynamics models with heritable trait variation and phenotype-dependent 117 interactions between individuals" (Lamarins et al., 2022a), have emerged as an effective framework to study management strategies while being spatially explicit and integrating eco-evolutionary feedbacks. DG-ABMs have been used to investigate the consequences of 120 exploitation but mainly at population scale (e.g., Thériault et al., 2008;Marty et al., 2015;Ayllón et al., 2019;Piou et al., 2015). ...

Importance of interindividual interactions in eco‐evolutionary population dynamics: The rise of demo‐genetic agent‐based models

... It can limit the risk of extinction and aid in colonisation, but it can also influence local population dynamics, the stability of a set of interacting populations, and adaptive potential. Conversely, effective dispersal (i.e., gene flow) can alter local adaptation and homogenise populations (Benton & Bowler, 2012;Garant et al., 2007;Lamarins et al., 2022;Webster et al., 2017). To better understand the dynamics of any given local population, it is therefore necessary to consider its metapopulation context. ...

Implications of dispersal in Atlantic salmon: lessons from a demo-genetic agent-based model

... Using another mathematical model, Haramboure et al. 26 found that the release of sterile males coated with pyriproxifen was more effective than SIT to control A. albopictus (Skuse 1894) mosquitoes in La Réunion when sterile males are poorly competitive, and that the optimal window to start the control period could be extented. Using an agent-based model, Diouf et al. 27 showed that SIT and boosted SIT relying on the used of entomopathogenic fungal spores could successfully reduce fruit fly populations of the Oriental fruit fly, Bactrocera dorsalis (Hendel 1912) and fruit infestation in mango orchards. However, more explorations of the performance and economical returns of the boosted SIT are still needed. ...

An agent-based model to simulate the boosted Sterile Insect Technique for fruit fly management
  • Citing Article
  • March 2022

Ecological Modelling

... In some cases, they may also be considered as pests that are detrimental to an ecosystem, such as an agricultural ecosystem (e.g. plagues of locusts [5]). Therefore, monitoring their movement behavior and migration patterns can help to understand and improve ecosystems. ...

Seeing the locust in the swarm: accounting for spatiotemporal hierarchy improves ecological models of insect populations