Brévault, Thierry

Research projects

I have been working for ten years in basic and applied research on insect biology, behaviour, ecology, population genetics, and management, from gene to population, from laboratory to farmer’s field, from plant to agricultural landscape. This experience allowed me to connect various skills so as to manage applied research programmes aimed at improving agricultural practices for sustainable crop production. 

Below is a sample of recently-completed and ongoing projects. Publications for completed work can be found on the publications page.


Conservation biological control: the millet head miner as a case study

The millet head miner, Heliocheilus albipunctella (Lepidoptera, Noctuidae), is a major constraint to increasing crop productivity in sub-Saharan Africa. In the absence of any insecticide application by farmers, millet production relies on natural pest control by predators and parasitoids. However, the continued delivery of such ecosystem service is threatened by biodiversity loss due to simplification of land uses and deforestation. A better understanding of factors driving natural pest control is a major challenge for reducing yield losses due to insect pests. Our research project mobilizes remote sensing, high spatial resolution satellite imagery, and land use surveys to explore the landscape dynamics (evolution on last decades) and resource use by stakeholders. A set of millet fields are monitored to identify local and landscape drivers of pest incidence and biological control. High-throughput molecular tools are used to document food web structures (including primary resources, other phytophagous pests and their natural enemies) and ecological processes underlying natural pest control. Next steps include farmer-participatory approaches to design farm- or land-scapes fostering natural pest regulation.

Collaborations : INRA-CIRAD-IRD UMR CBGP, Montpellier, France. ISRA-CNRA Bambey, Dakar, Senegal. CSE, Dakar Senegal.

  

 

Invasion of the tomato leaf miner, Tuta absoluta, in West Africa

 

The recent detection in Senegal of the tomato leafminer, T. absoluta, and its rapid geographic spread, is a real concern for tomato production in Africa south of the Sahara. To design integrated pest management strategies, it is essential to assess the role of source or sink of host plants (including wild secondary host plants) in the seasonal population dynamics of the pest across the agricultural landscape, the potential of indigenous natural enemies for biological regulation in the newly invaded area, and the effect of crop management on abundance of T. absoluta populations and conservation of indigenous natural enemies.

Collaborations : INRA UMR ISA, Sophia Antipolis, France. Virginia Tech, IPM Innovation Lab, USA. UCAD 2PIA, ISRA-CDH, Dakar Senegal.

 

Bollworm resistance to transgenic Bt cotton

Widely grown transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt) can benefit agriculture, but adaptation by pests threatens their continued success. Although most pest populations remain susceptible, reduced efficacy of Bt crops caused by field-evolved resistance has been reported now for some populations of 5 of 13 major pest species examined, compared with resistant populations of only one pest species in 2005. Field outcomes support theoretical predictions that factors delaying resistance include recessive inheritance of resistance, low initial frequency of resistance alleles, abundant refuges of non-Bt host plants and two-toxin Bt crops deployed separately from one-toxin Bt crops. In addition, block refuges may be more effective than seed mixtures for delaying resistance in pests with mobile larvae and inherently low susceptibility to the toxins in Bt crops. The results imply that proactive evaluation of the inheritance and initial frequency of resistance are useful for predicting the risk of resistance and improving strategies to sustain the effectiveness of Bt crops. 

Collaborations : University of Arizona, Department of Entomology, USA. 

 

Ecological specialization in the cotton aphid

In Cameroon, I investigated the influence of spatial and temporal habitat heterogeneity in a cotton-growing agroecosystem on the genetic variability of the cotton aphid, Aphis gossypii Glover. Genetic structure of field populations was assessed using microsatellite markers while insecticide resistance was estimated through the detection of specific mutations. Results showed that A. gossypii populations are strongly structured into host races. In addition, the main genotype found on cotton presented multiple resistances to various insecticides and was able to move among asynchronous suitable habitats in response to changes in resource availability. The identification of host races, non-cotton refuges and resistance patterns will likely boost aphid management strategies in sub-Saharan Africa, where this pest is responsible for serious damage to cotton and vegetable crops.

Collaborations : INRA UMR 1301, Interactions Biotiques et Santé Végétale, Sophia Antipolis, France.

 

Pyrethroid resistance in the cotton bollworm

In Cameroon, I studied factors affecting the spread of insecticide resistance across populations of the cotton bollworm, Helicoverpa armigera Hübner (Lepidoptera: Noctuidae). This insect is a major pest of several crops including cotton, maize, and a range of vegetables in Africa, Asia, southern Europe and Australia. It has developed high resistance to most insecticides deployed for its control, thus gaining an important pest status. In central Africa, severe control failures were reported in cotton during the 2004 growing season. Laboratory bioassays and enzymatic analyses demonstrated that the overproduction of esterase enzymes was responsible for resistance to pyrethroids, that resistance was dominant and associated to significant fitness costs. An innovative approach based on the combination of resistance (monitoring), molecular (microsatellites), and chemical (carbon isotopes and gossypol) markers, clearly showed host switching and dispersal to more northern locations as the growing season progressed. In addition, no genetic structuring associated with host or distance was detected. These findings are highly relevant for the management of resistance to both synthetic and natural insecticides in H. armigera, including transgenic Bt-producing crops.

Collaborations: IRAD, PRASAC-ARDESAC, Cotton Program, Garoua, Cameroon; IRD, UR 016, CREC, Cotonou, Benin; UMR 1301 INRA-CNRS-UNSA, Sophia Antipolis, France; Department of Entomology, University of Arizona, Tucson, USA.

  

Host location in specialist fruit flies

During my PhD, I developed various methods to study strategies used by insects to find egg-laying sites. I showed that females of the tomato fruit fly, Neoceratitis cyanescens Bezzi (Diptera: Tephritidae), evolved mechanisms using independently or interactively olfactory and visual signals to find suitable host plants. After locating host patches by tracing specific host fruit odour carried by wind, females land on the fruit on the sole basis of vision. These results could be used for developing efficient trapping systems for monitoring tomato fruit fly females or attract-and-kill strategies in commercially grown tomatoes.

Collaborations: UMR PVBMT CIRAD-Université de La Réunion, Saint-Pierre, La Réunion, France.

 

Soil macrofauna communities

in direct seeding mulch-based systems

Systematic exportation, burning of crop residues and decreases in fallow periods have led to a large-scale depletion of soil organic matter and degradation of soil fertility in the cotton cropping systems of sub-Saharan Africa. We found that no-till with mulch soil management strategy favoured the establishment of diverse macrofaunal communities in some cotton cropping systems.

Collaborations: IRAD, PRASAC-ARDESAC, Cotton Program, Garoua, Cameroon; SODECOTON, ESA, Garoua, Cameroon; CIRAD, UMR CBGP, Montpellier, France.

 

Sequential pegboard to support small farmers

in cotton pest control decision making

A method (SPID) based on sequential plan for individual decision with a pegboard was tested over the 2006, 2007, and 2008 cropping seasons in 45 cotton producing villages in Cameroon to help farmers decide on when to spray their cotton crops against bollworms. This method is not hampered by the constraints experienced with the former LEC (‘targeted staggered control') spraying decision method - sequential sampling reduces the number of plants to be monitored, spraying decisions are made for individual plots, income rises and the role of supervisors is reduced.

Collaborations: IRAD, PRASAC-ARDESAC, Cotton Program, Garoua, Cameroon; SODECOTON, ESA, Garoua, Cameroon; CIRAD, UMR PVBMT CIRAD-Université de La Réunion, Saint-Pierre, La Réunion, France.

 

Photos by A. Franck and T. Brévault