Progress 10/01/04 to 09/30/05
Outputs
In 2005 we manipulated the evolution of resistance in four fields, three in Freyberg ME and one in Water Mill NY, by treating half of each field with in-furrow imidacloprid at planting. Eggs were collected and hatched in early July. We assayed 25,800 2nd instar larvae for resistance using a 1 microliter drop of imidacloprid dissolved in acetone at doses in the range of 3.0e-6 to 2.0e-4 g/ml, to determine LD50 curves for each clutch at different distances from the treatment boundary. These values are fit by their geographic locations in the field to models of the evolution of resistance, to estimate dispersal and gene flow parameters. Resistance on the treated side of the field evolved to 1.4x the untreated sides in ME and 1.8x in NY, with considerable patchiness within fields. Treated and untreated sides were less resistant than in 2004. Data analysis for evolution of cline shape in the fields is in progress. To estimate overwintering costs of resistance, we used
sperm precedence to compare resistance of stored sperm from fall matings in Long Island to sperm from naturally overwintered, spring-emerged males. Larvae of mated females were 2.4x as resistant as larvae of unmated females, suggesting that adults in the fall were 5.9 times as resistant as emergers the following spring. The overwintering cost of carrying a resistant genotype is therefore likely to be quite high. The following undergraduates were trained: Jeff Ahern (UMass), Nehal Galal (CUNY-Queens), Diana Ramroop (Louis Stokes Alliance for Minority Participation fellowship). Also trained: Bushra Wazed, Krystal Lum (Townsend Harris High School, NY).
Impacts
We have trained 8 undergraduate research assistants and 2 high school students. We will publicize our field tests of the costs and benefits of refuges and mixed treatments. The results of our study will lead to specific recommendations for spatial scale of refuges and treated areas, predictions of resistance evolution in Potato beetle to imidacloprid and other insecticides, and a strong recommendation as to whether refuges must be planted adjacent to treated areas or can be planted significant distances from them.
Publications
- No publications reported this period
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Progress 09/15/02 to 09/14/05
Outputs
This research has generated valuable data for our understanding of the evolutionary dynamics of resistance to imidacloprid in Colorado Potato Beetle. These funds permitted us to create clines in pesticide resistance and allow us to measure microevolutionary parameters from the resulting cline shape. They also provided funds for the thorough study of mating preference, overwintering ability, and associated fitness costs for resistant beetles. These funds also supported development of analytical models, and associated computational software (that is still in development) for sophisticated analysis of microevolutionary forces. When data analysis is complete, we will develop the computational models for optimal refuge placement using those resulting dispersal and selection parameters. As this project terminates, we have accumulated large data sets on resistance evolution in 20 treated fields (some funded from other sources), 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. This approach takes advantage of the fact that spring females carry sperm from fall matings, and remate as well. Offspring of remated females were significantly less resistant, indicating
higher mortality in resistant males. This paper is in review. 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. Inheritance is a key element in the microevolutionary models. This paper is in review. 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
This project has uncovered important fitness costs of resistance that significantly impact its microevolutionary dynamics of resistance. The expected measures of dispersal rates of resistant and susceptible beetles will permit us to parameterize models to optimize the placement of refuges to slow the evolution of resistance. The work trained several undergraduate students in scientific investigation, one of whom is now a PhD student in plant-insect interactions.
Publications
- Baker, M. B., A. Alyokhin, S. R. Dastur, A. H. Porter & D. N. Ferro. 2005. Sperm precedence in overwintered Colorado Potato Beetle (Coleoptera: Chrysomelidae) and its implications for insecticide resistance management. Annals of the Entomological Society of America 98: 989-995.
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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, with the pesticide bioassays from both areas carried out in MA. Work went according to schedule in ME, but due to circumstances beyond our control we fell behind in MA. Due to our setback, we will use a no-cost extension to fund the MA work in 2005. Progress towards Objectives: IA: Model development: The likelihood software is being written. IIA: Create replicate clines 4 clines were set up in Fryberg ME, 2 from NRI funds. We collected up to 50 clutches from 22 locations in each field, and assayed 14,582 larvae. The LD50 of treated fields was 1.45 times that of untreated fields. Clines were detectable by eye prior to in-depth analysis via likelihood. IIB: Calibrate dose-response curves. The data are collected and awaiting analysis. IIC: Treatment-specific adult movement These experiments were postponed for a year and will be carried out as a part of the extension. 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. IV: refuge design recommendations Co-PI Baker has simulated refuge designs to test their sensitivity to biologically relevant parameters, including variation in field rotation, contiguous refuges versus those separated by varying amounts of low-host-density matrix, and the presence of dispersal polymorphisms. While much depends on individual parameters of the system, a general pattern emerged where optimal design depends on the ratio of dispersal rate to refuge spacing. Conditions that insulate refuges from treated areas sometimes enhance refuge success. The pattern is non-linear; even small deviations from optimal design have major negative impacts on resistance evolution. Refuges should therefore
be designed from a risk-averse perspective.
Impacts
We have trained 6 undergraduate research assistants and will train a similar number next year. We will publicize and test in the field the costs and benefits of refuges and mixed treatments. The results of our study will lead to specific recommendations for spatial scale of refuges and treated areas, predictions of resistance evolution in Potato beetle to imidacloprid and other insecticides, and a strong recommendation as to whether refuges must be planted adjacent to treated areas or can be planted significant distances from them.
Publications
- No publications reported this period
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Progress 10/01/02 to 09/30/03
Outputs
Our project creates clines in resistance to imidacloprid by planting fields consisting of imidacloprid treated and untreated sides. The clines will be analyzed to extract dispersal and gene flow data, and develop optimal refuge crop designs to slow the evolution of resistance to imidacloprid and other treatments in Colorado potato beetle and other insect pests. 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 developed a model of resistance evolution in refuge based systems that incorporates costs of resistance, different crop rotation strategies (rotating crops versus rotating treatments), barriers to movement between the refuge and treated area, and several other factors, in each case asking how variation in dispersal influenced resistance evolution. We found that changing the additivity of resistance, the toxicity of the treatment, the size of the refuge, the costs of resistance, and the initial resistance frequency all greatly affected refuge success, but did not change the optimal spatial scale of treated areas relative to the dispersal of the insect. Different rotation
strategies, and barriers to movement between refuges and treated areas, do affect the optimal spatial scale of refuges and treated areas, and these relationships are under continuing investigation. 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.
Impacts
We have trained 6 undergraduate research assistants and will train a similar number next year. Our collaborations with growers will publicize and test in the field the costs and benefits of refuges and mixed treatments. The results of our study will lead to specific recommendations for spatial scale of refuges and treated areas, predictions of resistance evolution in Potato beetle to imidacloprid and other insecticides, and a strong recommendation as to whether refuges must be planted adjacent to treated areas or can be planted significant distances from them.
Publications
- No publications reported this period
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Progress 10/01/01 to 09/30/02
Outputs
Project is new.
Impacts
(N/A)
Publications
- No publications reported this period
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