Progress 03/01/01 to 09/30/06
Outputs
This research has generated valuable data for our understanding of the evolutionary dynamics of resistance to imidacloprid in Colorado Potato Beetle. The funds on this grant have played supporting roles for larger investigations of this question, funded by other sources. These funds permitted the gathering of sufficient pilot data demonstrating the feasibility of our approach, which was to create clines in pesticide resistance and measure microevolutionary parameters from the resulting cline shape. They also provided funds to initiate satellite studies of mating preference, overwintering ability, and associated costs for resistant beetles, as well as helping us accumulate families of known resistance genotype for molecular genetic analysis. The larger studies are devoted to building replication among fields and populations, significantly more sophisticated theoretical and computational analysis of the problem, and thorough study of the costs of resistance. As this
project terminates, we have accumulated large data sets on resistance evolution in 20 treated fields (funded elsewhere), of which 12 showed appropriate responses. In the remainder, 3 were unusable because the resident population had so little background resistance that the population was wiped out on the treated side; we were defrauded by the grower on 3 fields in South Deerfield, MA (who we confirmed had applied pesticide to the entire field, not half), and we believe the remaining 2 fields in ME also were fully treated. We are using other funding sources to increase the sample size of usable fields to 15 before initiating the computationally intensive data-analysis phase. The approach works: preliminary analysis indicates that resistance has evolved on several of these fields; others are ambiguous pending full analysis. We measured reproductive success in of males that had overwintered in diapause, and found significantly lower survivorship in resistant males. We measured the
inheritance of resistance; partly covered by these funds. We found resistance to be polygenic, and evidence that modifier genes had evolved between 1999 and 2004 that affected hatching success of resistant beetles. Our undergraduate honors student at UMass, Jeff Ahern, determined that the beetles were unlikely to be able to distinguish and avoid treated foliage, whether by taste or by the resulting physiological effects of ingestion. He is now a PhD student at Rice University, studying plant-insect interactions.
Impacts
When the analyses are finished, we believe this will give much clearer insight into the complex evolutionary dynamics underlying the evolution and spread of resistance. The high costs of resistance we find imply that significant evolutionary trade-offs are taking place, and are likely to mitigate impact even of resistant beetles (at least, until compensatory evolutionary changes restore their fitness). The measurement of dispersal rates of resistant genes will permit us to parameterize models of refuge design, optimizing refuge size and placement. The funds have contributed to the education of several undergraduate students, one of whom has gon on to graduate study in a closely related field.
Publications
- No publications reported this period
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Progress 10/01/04 to 09/30/05
Outputs
Our project studies the evolution of resistance to imidacloprid in Colorado potato beetle in both commercial and experimental fields, and in laboratory studies of resistance costs and mating behavior. We developed our lab for assaying larger numbers (up to 2,000/day) of Potato beetle larvae and the rearing cages and facilities for maintaining 10 colonies of 150 adults or 400 larvae each. We surveyed imidacloprid resistance in Maine and Long Ialand NY, growing families for breeding experiments on the genetics of resistance, and assaying their resistance status using dose-response curves on offspring. We developed backcross lines to assay genetic markers for resistance, and are performing additional replicates prior to molecular genetic work. We also assayed the offspring of females mated in situ in the fall vs. those mated to overwintered males. Offspring of fall matings were almost 3x more resistant, implying a strong cost of resistance during adult overwintering. An
honors student (J Ahern, UMass) completed his thesis on the ability of beetles to detect imidicloprid in the foliage and avoid feeding upon it. If found, this behavior could have important implications of how resistance to pesticide is mediated and evolving in the patchwork of pesticide-treatment methods among fields in potato-growing regions. However, no evidence was found that beetles could detect or avoid the pesticide.
Impacts
We will derive estimates for the strength of selection for resistance to imidacloprid in Massachusetts fields. We are educating students in the evolutionary dynamics of pesticide resistance.
Publications
- No publications reported this period
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Progress 10/01/03 to 09/30/04
Outputs
We planned experiments in replicate fields in ME and MA for this summer as part of a larger NRI-supported study (Porter et al.), with the pesticide bioassays from both areas to be carried out in MA; these MAES funds support MA work. Experiments went according to schedule in ME, but research in MA was temporarily delayed. Experimental work: MAES funds supported office assistance for manuscript preparation by Ferro, as well as lab assistance (undergraduate M. Rosenbusch) and supplies. This winter and spring, with partial support from MAES funds, honors student Jeff Ahern will test the ability of CPB to recognize pesticide-treated foliage and modify their behaviors in response. To the extent that pesticide can be avoided, we predict this will increase the dispersal rates of beetles in treated vs. untreated fields. MAES funds contributed to lab supplies for experiments on relative fitnesses of resistant and susceptible beetles. Fecundities (a measure of fitness) of
resistant MA and ME populations were 36.8 (SE3.7) and 40.0(3.8) vs. 56.6(3.0) eggs/day in susceptible beetles, but hatching success did not differ. This predicts a stable polymorphism of resistant and susceptible beetles, and explains why resistance has not risen to 100% in MA. Sperm-precedence: Mated CPB females overwinter and emerge capable of laying fertile eggs. We showed that if they do mate in the spring, those new matings have almost complete precedence over stored sperm. If overwintered adults from refuges and treated areas mix as they colonize spring fields, and resistant genotypes have lower survival (which we are testing separately), this will reduce resistance levels in the spring offspring. This facilitates the refuge effect in resistance management. The manuscript in is revision.
Impacts
We will derive estimates for the strength of selection for resistance to imidacloprid in Massachusetts fields. We are collaborating with one local grower, to experiment with mixed/partial treatment fields to slow the evolution of insecticide resistance.
Publications
- No publications reported this period
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Progress 10/01/02 to 09/30/03
Outputs
Our project studies the evolution of resistance to imidacloprid in Colorado potato beetle in both commercial and experimental fields, and in laboratory studies of resistance costs and mating behavior. We developed our lab for assaying larger numbers (up to 2,000/day) of Potato beetle larvae and the rearing cages and facilities for maintaining 10 colonies of 150 adults or 400 larvae each. We surveyed imidacloprid resistance in Maine and western Massachusetts (9000 larvae from 5 fields in Maine and 19 fields in Massachusetts) and found similar levels of resistance as in 2001 in Massachusetts, a surprising result given the number of years imidacloprid has been in use. Resistance to imidacloprid in most areas in Maine was much lower than even untreated (with imidacloprid or related insecticides) fields in Massachusetts, but fields near the town of Freyburg, ME, have been located with high levels of resistance that will be ideal locations for creating resistance clines in
2004. We secured a 55-acre field in Massachusetts for the creation of imidacloprid resistance clines on 4 fields separated by roads or corn in 2004. We used a sterile male technique to investigate mating competition and gene flow between resistant and susceptible beetles. Imidacloprid-resistant and susceptible males were placed with either virgin susceptible females on untreated plants, or virgin resistant females on treated plants, for 24 hours, and mating behavior and subsequent hatch rates were recorded. Resistance to imidacloprid does not appear to convey mating costs on untreated foliage; resistant males mated just as frequently and sired as many offspring. Treated foliage is a strong barrier to gene flow, as resistant males were much more likely to mate and sired the vast majority of offspring when the contests were staged on treated plants. We are in the middle of a 10 generation drift experiment. We started with a population of fairly resistant CPB (12 times as resistant as
the most susceptible field populations in Massachusetts, and 34 times as resistant as the most susceptible fields in Maine). We divided the resistant line into two lines. Each line is maintained at 60-100 adults each generation, and similarly sized susceptible lab colonies are assayed each generation.
Impacts
We will derive estimates for the strength of selection for resistance to imidacloprid in Massachusetts fields. We are collaborating with at least one local grower and possibly others, to experiment with mixed/partial treatment fields to slow the evolution of insecticide resistance.
Publications
- Boiteau G., Alyokhin A., Ferro D. N. 2003. The Colorado potato beetle in movement. Canadian Entomologist 135: 1-22.
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Progress 10/01/01 to 09/30/02
Outputs
This year we developed a more sophisticated mathematical and statistical model of the evolution of cline shape (Objective 2A). We will apply this model to data from new experiments on the evolution of resistance in artificial clines. The model was used as a basis for grant proposals to USDA/NRI and NSF to fund these new experiments. These proposals have been funded (USDA/NRI) or recommended for funding (NSF) and the experiments will start in May 2003. These experiments will involve the study of evolutionary changes in resistance in 20 fields in Massachusetts and Maine over the next 2-year period.
Impacts
Our study of the evolution of resistance addresses basic-science issues by enhanding our understanding of rapid evolutionary change under non-equilibrium conditions. This knowledge is critical for understanding the evolution and spread of resistance, which evolves to prevalence very rapidly once it emerges in a species. This research moves applied science goals forward by providing us with a measure of the spread of resistance within fields. From this measure, we will be able to recommend the optimal size and placement of refuges for the control of the evolution of resistance.
Publications
- No publications reported this period
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Progress 10/01/00 to 09/30/01
Outputs
New Project
Impacts
(N/A)
Publications
- No publications reported this period
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