Progress 08/01/07 to 07/31/12
Outputs
OUTPUTS: Results of this research have been presented to extension entomologists in Arizona, who will relay the information to cotton growers. The publications and scientific presentations arising from this research will be useful for EPA and University scientists as well as members of the Industry working in the field of resistance management for arthropod pests. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Since 1996, the Environmental Protection Agency has mandated that farmers in the United States who plant Bt crops, which make insecticidal proteins from the bacterium Bacillus thuringiensis (Bt), also plant refuges. EPA regulations stipulate the proportional area of refuges to be planted in a region and the maximum distance between refuges and Bt crop fields. However, until now, precise methods to identify habitats that are efficient refuges and the maximum distance at which such refuges can delay the evolution of resistance had been lacking. Also, no field test of the refuge strategy had been conducted. For the first time, we tested the refuge strategy in the field using eight years of data on the distribution and abundance of crops, application of pyriproxyfen, and whitefly resistance to pyriproxyfen. Pyriproxyfen is an insect growth regulator that targets sweetpotato whiteflies, a key pest of cotton and other crops in Arizona and worldwide. It is applied once in cotton during the growing season, which limits the selective pressure for resistance evolution. It is also a specific insecticide that contributes in preserving natural enemies of cotton pests. We first developed spatially-explicit, statistical models based on four years of data that included aerial remote sensing maps and documented pesticide applications in Central Arizona. The resulting statistical models identified the crops affecting the spatial variation in resistance and the maximum distance at which these crops affected resistance. In a second step, we used these models and a data set from the next four years to predict spatial variation in resistance at the landscape level. The successful prediction of resistance confirmed that refuges of cotton delayed the evolution of resistance and fields treated with pyriproxyfen accelerated the evolution of resistance. The developed method and framework is general and could help refine the refuge strategy used to delay the evolution of resistance to Bt crops and insecticides in many key pests in the US.
Publications
- Carriere, Y., Ellers-Kirk, C., Harthfield, K., Larocque, G., Degain, B., Dutilleul, P., Dennehy, T. J., Marsh, S. E., Crowder, D. W., Li, X., Ellsworth, P. C., Naranjo, S. E., Palumbo, J. C., Fournier, A., Antilla, L., and B. E. Tabashnik. 2012. Large-scale, spatially-explicit test of the refuge strategy for delaying insecticide resistance. Proceedings of the National Academy of Sciences USA. 109: 775-780.
- Crowder, D. W., Horowitz, A. R., Bresulauer, H., Rippa, M., Kontsedalov, S., Ghanim, M., and Y. Carriere. 2011. Niche partitioning and stochastic processes shape community structure following whitefly invasions. Basic and Applied Ecology. 12:685-694.
- Heuberger S., D.W. Crowder, T. Brevault, B. E. Tabashnik, and Y. Carriere. 2011. Modeling the effects of plant-to-plant gene flow, larval behavior, and refuge size on pest resistance to Bt cotton. Environmental Entomology. 40: 484-495.
- Crowder D., Ellsworth P., Naranjo S., Tabashnik B., Carriere Y. 2012. Modeling resistance to juvenile hormone analogs: linking evolution, ecology, and management. In: Devillers J., ed. Juvenile Hormones and Juvenoids: Modeling Biological Effects and Environmental Fate. CRC Press, Boca Raton. In press.
- Brevault, T., Nibouche, S., Achaleke, J. and Y. Carriere. 2012. Assessing the role of non-cotton refuges in delaying Helicoverpa armigera resistance to Bt cotton in West Africa. Evolutionary Applications. 5: 53-65.
- Williams J. L., Ellers-Kirk C., Orth R. G., Gassmann A. J., Head G., Tabashnik B. E., and Carriere Y. 2011. Fitness cost of resistance to Bt cotton linked with increased gossypol content in pink bollworm larvae. PLoS One. 6(6): e21863. doi:10.1371/journal.pone.0021863
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Progress 08/01/09 to 07/31/10
Outputs
OUTPUTS: During this funding period, we have completed Objectives 4 and 5: Model the relationship between distribution and abundance of crops, use of pyriproxyfen, and pyriproxyfen resistance in the whitefly, and test the empirical model by comparing predicted vs. observed resistance in the field. We are currently working on the final Objective of the proposal: Estimate the extent of whitefly dispersal between various crops (refuges) and cotton fields. Because whiteflies are small insects that use wind to disperse, we are evaluating potential effects of wind direction on refuge efficacy. We have developed and are applying a novel GIS-based method to weigh crop fields by wind direction. We expect this Objective to be completed by the end of this funding period. One publication has been written for Objectives 4 and 5. Results have been presented to relevant entomologists in Arizona and will be presented more broadly at conferences and invited talks in the US and abroad. We plan to write another publication and report results in a similar manner when Objective 6 will be completed. PARTICIPANTS: One MSc student (Kyle Hartfield) working on remote sensing and funded by this project has graduated during this funding period. He was involved in the development of novel techniques for retrospective identification of crops. He has submitted a MS on these techniques recently. One research specialist working on GIS and remote sensing aspects of the project was partially funded by the project. TARGET AUDIENCES: Results have been presented to extension entomologists in Arizona, who will relay the information to cotton growers. The publications and scientific presentations arising from research accomplished during this funding period will be useful for EPA and University scientists as well as members of the Industry working in the field of resistance management for arthropod pests. PROJECT MODIFICATIONS: No major modifications to the proposal were done.
Impacts
The spatially-explicit approach developed in Objectives 4 and 5 can be used for testing and improving refuge strategies for pests targeted by Bt crops and insecticides. The method provides a systematic assessment of the effectiveness of refuges and the scale of their effects. This approach applied to the whitefly system has allowed us to test and improve the refuge strategy for managing resistance to pyriproxyfen in Arizona. This approach will likely be useful for testing and improving the refuge strategy in other crop-pest systems.
Publications
- Crowder, D. W., M. I. Sitvarin, and Y. Carriere. 2010. Mate discrimination in invasive whitefly biotypes. Journal of Insect Behavior. 23: 364-380.
- Carriere Y., D. W. Crowder, and B. E. Tabashnik. 2010. Evolutionary ecology of adaptation to Bt crops. Evolutionary Applications. 3: 561-573.
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Progress 08/01/08 to 07/31/09
Outputs
OUTPUTS: Objective 1 and 2: Over the past year three methodologies for identifying crops in Pinal County Arizona have been explored using remotely sensed images. Utilizing data sets acquired in 2008 and 2007, and previously acquired data (2002), we evaluated the comparative accuracy of these three classification techniques. The method that performed best is a Classification and Regression Tree (CART) classifier. Training of the classifier was performed by selecting 20 percent of fields off of a reference map and using the other 80 percent of fields to assess the accuracy of the final classification results. The classifier was run to identify cotton, alfalfa, grain, fallow, corn, melons, orchards, and sorghum. Overall classification accuracy results were 83%, 85%, and 86% for 2002, 2007, and 2008 respectively. Additional derived data were also added to the CART classifier for the years of 2007 and 2008 which lead to overall accuracies of 86% and 87%, respectively. Further research is in progress to determine whether sampled fields from one year can be used to identify crop types from a different year in the same study area. Preliminary data provide good accuracy for retrospective identification of cotton and alfalfa (>90%) but not melons. Objective 3: We have obtained data on pyriproxyfen applications in Arizona from 2006-2008 from the State of Arizona's Pesticide Use Reporting (PUR) database and will analyze these data in the coming year. Objective 6: We used GPS and GIS to map all crops that are whitefly hosts (melon, alfalfa, cotton) at a distance of 3 km form 55 focal cotton fields in Maricopa for both 2008 and 2009. Whiteflies were weekly sampled in each focal field 6-8 times between July 1 and August 15. We have developed software to analyze these data and determine the zone of influence of refuges in 2008 and 2009, as described in the proposal. In addition to the work outlined above, we have used simulation models to develop the refuge theory as it applies to haplodiploid insects such as the whiteflies, and extended results to parthenogenetic pests as well. We have also conducted research on the competitive interaction between biotypes of the whitefly. Reproductive interference between the B and Q biotype of the whitefly could have important impacts on the ability of the Q biotype to invade field crops such as cotton in the US. Currently the B biotype exploits cotton and other field crops the Q biotype is present in greenhouses across the U.S. We hypothesized that reproductive interference could affect coexistence between these two biotypes, with the inferior biotype being displaced from shared habitats, a process known as sexual exclusion. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Using simulation models, we have demonstrated that the tenets of the standard refuge strategy apply to all pests. However, this strategy does not greatly delay the evolution of resistance in haplodiploid or parthenogenetic pests, unless two additional factors are present. Refuges must induce fitness costs, and transgenic (GM) crops (or insecticides) must induce incomplete resistance such that resistant individuals have lower fitness on GM compared to non-GM crops. These results indicate that the sustainability of GM crops or insecticides that target haplodiploid or parthenogenetic pests will require careful consideration of the effects of reproductive mode, fitness costs, and incomplete resistance. We determined the role of reproductive interference on mating success and sexual exclusion between the B and Q biotype present in the U.S. We showed that females of the B biotype were more successful at mating than females of the Q biotype when reproductive interference was present. The ability of B females to mate more successfully than Q females allows them to produce more female offspring, which ultimately could lead to sexual exclusion of other biotypes. Our results could aid in understanding the distribution and spread of these invasive pests.
Publications
- Crowder, D. W., M. I. Sitvarin, and Y. Carriere. 2010. Plasticity in mating behavior drives competitive displacement of whitefly biotypes. Animal Behaviour, in press
- Crowder, D. W. and Y. Carriere. 2009. Comparing the refuge strategy for managing the evolution of insect resistance under different reproductive strategies. Journal of Theoretical Biology. 261: 423-430.
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Progress 08/01/07 to 07/31/08
Outputs
OUTPUTS: Objective 1: We have acquired several remotely sensed satellite (Landsat-5) images that encompass the study area. Initial image processing was completed utilizing ERDAS Imagine. Vector maps provided by the Arizona Cotton Research and Protection Council (ACRPC), with field crops identified for the respective years and areas, were used to mask the images and restrict processing to the area of field crops. Unsupervised classifications utilizing the ISODATA algorithm was conducted. ACRPC vector maps, with field crop types of interest (cotton and alfalfa), were employed to select training sites for subsequent supervised classifications utilizing a maximum likelihood algorithm. An accuracy assessment was run for both types of classification. An unsupervised classification was also run on a Yuma County image to determine image quality. As a minimal number of field crop types were identified on the vector map associated with this image, a Global Positioning System (GPS) was used to gather points to determine the position of field crop types in the Fall of 2007. Accuracy assessment statistics were lower than expected. In August of 2008, on-site work was performed both in Yuma and Pinal counties. Teams used GPS technology to gather points within the crop field types of interest. Satellite images of these regions near the time of the sample dates have been ordered. These improved GPS data, along with maps provided by the ACRPC, will be used to classify the images with greater accuracy then previously achieved. We are also testing two new classification softwares. The first is the automated image analysis software Definiens. It has been purchased and is now running on-site. The second software, Rulequest's See5.0 is a decision-tree based classification system that works in conjunction with ERDAS Imagine. It is currently used by the USDA-NASS in the production of their cropland data layers (CDLs) with positive results. Objective 3: We have extracted data on pyriproxyfen applications in Arizona from 2001-2005 from the State of Arizona's Pesticide Use Reporting (PUR) database. We used GIS to superimpose location of insecticide applications to the distribution of cotton fields across the state. We determined that accuracy of the location of application of pyriproxyfen at the section level, as reported by PUR, is likely less than 90%. We are currently evaluating how much of this inaccuracy is due to error in data entry, as opposed to error in reporting the location of insecticide applications. We plan to obtain and process PUR data for 2006 and 2007. Objective 6: We used GPS and GIS to map all crops that are whitefly hosts (melon, alfalfa, cotton) at a distance of 3 km form 55 focal cotton fields in Maricopa this summer. Whiteflies were weekly sampled in each focal field 6-8 times between July 1 and August 15. Once all insects are counted, we will perform spatially-explicit statistical analyses to assess the zone of influence of refuges in 2008, as described in the proposal. PARTICIPANTS: Christa Ellers Kirk, research specialist. Part of her work is used to obtain a MS certificate in Remote sensing. Kile HartField, MSc student. Two undergraduate student contributed to whitefly sampling. PIs directly involved in the work: Yves Carriere, Barron J. Orr, Stuart E. Marsh, Peter C. Ellsworth, John C. Palumbo and Bruce E. Tabashnik TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: None.
Impacts
All objectives are ongoing. We currently have no outcome/impact to report.
Publications
- No publications reported this period
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