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United States Department of Agriculture

Agricultural Research Service


Location: Plant Genetics Research

2013 Annual Report

1a.Objectives (from AD-416):
Develop colonies with resistance to Cry34/35Ab1 and test the effectiveness of two refuge types to delay resistance. Test the dominance and fitness costs of resistance to Bt corn.

1b.Approach (from AD-416):
Western corn rootworm colonies will be selected for resistance to Cry34/35Ab1-expressing transgenic maize and resistance levels will be compared to control colonies and colonies designed to simulate a refuge. In addition, dominance of resistance will be tested by crossing resistant and susceptible colonies and evaluating progeny and fitness costs associated with resistance will also be evaluated.

3.Progress Report:

This work is related to sub-objective 1.A of the parent project: “Develop colonies with resistance to Cry34/35Ab1 and test the effectiveness of different refuge types to delay resistance” and contributes to Component 2A of the National Program 304 Action Plan by developing increased knowledge of the biology, ecology, behavior, and genetics of pests, and plant traits conferring pest resistance.

Transgenic corn is effective in rootworm management but in order to maintain its effectiveness, “refuges” designed to delay resistance must be useful and well-designed. Understanding which “refuge” types of non-Bt corn are effective in delaying resistance can extend management options beyond that which would be otherwise possible. As reported in Project No. 3622-21220-007-04R, work is being duplicated in both Missouri and Iowa. The Iowa-only work is reported below.

Research has been conducted by ARS scientists to test fitness costs of resistance and inheritance of resistance in two strains of Cry3Bb1-resistant western corn rootworm and two Cry3Bb1-susceptible stains. In both cases resistance was found to be non-recessive. Fitness costs have been tested in the presence of entomopathogenic (insect pathogens) nematodes and fungi, and among different lines of corn. Measurements were recorded for adult size, developmental rate, egg hatch rate, egg viability, adult longevity and survival to adulthood. In general, evidence for fitness costs was not detected, which is an important finding because it increases the likelihood of resistance developing in the insect population and will allow resistance alleles to persist once they are present.

Last Modified: 7/28/2014
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