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Le Criquet du Mato Grosso. Bilan et perspectives de 4 années de recherches : 1992-1996. Rapport final du projet « Environnement et criquets ravageurs au Brésil ».
Abstract
This book "O gafanhoto do Mato Grosso" is available in portuguese at : https://www.embrapa.br/busca-de-publicacoes/-/publicacao/16721/o-gafanhoto-do-mato-grosso-balanco-e-perspectivas-de-4-anos-de-pesquisas-1992-1996
Studies conducted within the framework of the EMBRAPANMA/EC/CIRAD-GERDAT-PRIFAS project, entitled "Environment and Pest Locusts and Grasshoppers of Brazil", have focused on Rhammatocerus schistocercoides (Rehn, 1906). This is an important pest grasshopper of Mato Grosso state (Brazil) where outbreaks were, until present, explained as being a consequence of deforestation and accelerated agricultural development that has occurred since the early 1980s.
Many results obtained in this project refute previous hypotheses, especially concerning the assumption that grasshopper outbreaks are a recent phenomenon in Mato Grosso, that agricultural development has had an important impact on the grasshopper situation, and that these grasshoppers are a potential threat to neighbouring states.
Some of the main results obtained in this project are:
- The evidence that R. schistocercordes outbreaks are a long-standing phenomenon in Mato Grosso; they are in no way a new phenomenon prompted by the recent agricultural development in this region.
- The understanding of the relationships between land use (agricultural, pastoral and traditional) and grasshopper outbreaks.
- The findings concerning factors that determine grasshopper outbreaks, which seem to be mainly associated with the rainfall regime, especially from August to October, a critical period for the grasshopper cycle.
- The clarification of many points concerning the biology and ecology of this grasshopper; especially the finding that swarm movements are much more limited than previously assumed; considerable data has been collected on imaginal diapause, sexual maturation, development times for various biological stages, the number of instar stages, the
absence of phasal polymorphism, etc.
- The mapping of grasshopper biotopes (breeding biotopes and dry season refuge biotopes), essential for understanding the consequences of agricultural development in outbreak zones and basic documenls required for organizing efficient grasshopper survey
and control operations as part of a renovated control strategy.
The results of this project will have a critical operational impact. Strategies to control Rhammatocerus schistocercoides should now be completely reconsidered, while promoting local preventive spot treatments. There is considerable research potential in continuation of the currenl project, i.e. to perfect grassnopper outbreak survey, early-detection (high temporal resolution satellites) and grasshopper control (mycopesticides) techniques.
Overall, the results of this project have been the topic of twelve scientific publications, six confetence papers, fourteen maps (covering an area of about 145 000 km') and nineteen unpublished reports. Several publications are currently in preparation along with various other communications documents.
... The 2013-2015 plague is an example of a situation in which surveys were needed far from the permanent breeding area. 80 Another interesting species is Rhammatocerus schistocercoides (Rehn, 1906), 81,82 which has two very similar outbreak areas, one in central-western Brazil 83,84 and the other in the Llanos region of Colombia, which spills over a little into Venezuela. 85,86 In both areas, major outbreaks occurred in the 1980s in Brazil and in the mid-1990s in Colombia. ...
BACKGROUND
Poorly organised risk management system may dysfunction when used. The consequences can be dramatic for those supposed to be protected. Since the 1960s, preventive control strategies, which field officers are the living memory, have been developed to monitor locusts. Preserving their experience of past plagues is consequently essential. Wrong use of their knowledge can disrupt the whole management chain. We explored these conditions using a multi-agent model representing a preventive system. We simulated how the field teams’ tendency to repeatedly visit past outbreak areas (hotspots) by allocating them an attraction weight, can help in preventing plagues.
RESULTS
When field teams’ attention remained constant over time, there was dramatic decrease in the number of plagues with increasing interest in hotspots, as long as interest was less than 2.5 times more than elsewhere. When the field teams were only attentive during recession times, plagues were better controlled using a low weight for hotspots. The spatial structure of hotspot distribution had an effect: the more frequent and the bigger the hotspots, the lower the optimal hotspot weighting needed to reduce plagues.
CONCLUSION
Orienting surveys towards hotspots particularly during recession times reduces plagues. The spatial structure of locust habitats may influence the way to manage them. Habitats located outside the multiple hotspots of species such as the desert locust should be visited more frequently than those with only one hotspot, such as the South American locust. The decline/loss of the field officers’ experience highlights the need to save, capitalize and disseminate this knowledge.
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The problem posed in Brazil since 1984 by Rhammatocerus schistocercoides - an important pest locust in the Mato Grosso state - is exemplary. It shows how the occurrence of a new locust phenomenon has given rise to fruitless opposition between supporters of insecticide treatments, on one hand, and environmental conservationists on the other. Extensive control measures were implemented and large quantities of insecticides sprayed, with all of the drawbacks concerning risks to the environment and to the health of the indigenous people that eat locusts. Intensive ecological field work, carried out for l0 years, gradually has revised our understanding of the origin of this species' outbreaks and the way to control them. On the basis of solid scientific experience, solutions can now be posed that are realistic, efficient, respectful of the environment and the interests of farmers and indigenous populations.
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