Skip to main content
ARS Home » Southeast Area » Stoneville, Mississippi » Southern Insect Management Research » Research » Research Project #429232

Research Project: Innovative Strategies for Insect Resistance Management in Bt Cotton

Location: Southern Insect Management Research

Project Number: 6066-22000-085-00-D
Project Type: In-House Appropriated

Start Date: Jul 7, 2015
End Date: Jul 6, 2020

Objective:
Objective 1: Determine impacts of Bt toxins on pest insect biology, assess population dynamics, pest behavior, and host-plant relationships that enhance resistance, and develop management strategies to mitigate evolution of insect resistance to host plant expressed insecticidal genes. Sub-objective 1A: Determine the impacts of transgenic crops producing two or more Bt toxins on population ecology and phenology of heliothines in cotton. Sub-objective 1.B: Evaluate optimal management strategies to delay resistance of heliothines to transgenic cotton. Objective 2: Determine genetic diversity of bollworm populations and impacts of changes in allele frequencies of loci known to be associated with resistance to Bt toxins and insecticides. Sub-objective 2.A: Determine genetic diversity of bollworm populations and allele frequencies of loci known to be associated with resistance to Bt toxins and insecticides. Sub-objective 2.B: Evaluate the allele frequency changes during selection with Bt toxins and insecticides. Objective 3: Determine impacts of insecticide resistance on management of lepidopteran pests and develop environmentally sound strategies to manage pest complexes in transgenic cropping systems. Sub-objective 3.A: Determine impacts of insecticide resistance on management of bollworm. Sub-objective 3.B: Evaluate IPM tactics for optimal management of pests in transgenic cotton.

Approach:
The impacts of transgenic crops producing two or more Bacillus thuringiensis (Bt) toxins on population ecology and phenology of bollworm (BW) will be studied using replicated field experiments structured to examine multi-generational effects of selection by different sequences of transgenic crops (Bt-crops) and non-Bt crops. Experiments will be conducted using 1/16th acre field cages during the first three years of the project followed by five-acre field plots during the remainder of the project. Paired treatments will compare Bt-crop varieties with non-Bt counterparts (near isolines). Experimental crops inside cages will be infested with pupae reared from early season larval collections. Insect densities, species composition, survival on a given host, and crop damage data will be used to predict relationships between within-season selection of Bt-crop hosts and the effects of selection on population dynamics of BW. Sentinel plots of cotton and corn will be established on a spatial gradient representative of the range of latitudes within the Mississippi Delta and used to evaluate the effects of supplementary insecticide control of BW on primary Bt and non-Bt crop hosts. Different Bt crop varieties will be paired and planted with a non-Bt isoline. One replication of the Bt variety and its non-Bt isoline will be sprayed with chlorantraniliprole if and when recommended threshold for BW is reached. Other plots will receive no sprays for BW throughout the growing season. Non-target pests on the experimental plots will be controlled as needed with blanket applications of insecticides with no or low lepidopteran activity. Larval collections will be used to determine species composition infesting plots. Crop damage, species composition, and survival from each crop will be analyzed using each location as a replicate in a split plot design to determine the effects of supplementary control of BW in Bt and non-Bt crops on yield.Molecular markers will be used to evaluate genetic diversity of BW populations and impacts of changes in allele frequencies of loci associated with resistance to Bt toxins and insecticides. Allele frequencies in insects collected during the first three years of the project period will be compared with data from insects collected from 2002-2006. Identification of loci under selection will help us evaluate the impacts of field selection on BW over time. In addition, we will be able to estimate the mutation rates of the genes associated with Bt resistance and use those estimates in Bt resistance prediction models. A BW strain tolerant to Bt toxin Cry1Ac will be used to identify genomic regions responding to selection. Impacts of insecticide resistance on management of lepidopteran pests will be determined by mutating target receptor genes to generate insecticide resistance in BW lines with high tolerance to Bt toxins. Fitness costs of dual resistance will be evaluated using controlled experiments. Integrated pest management tactics utilizing various combinations of chemical and microbial agents will be evaluated to develop environmentally sound strategies to the management pest complexes in transgenic cropping systems.