Aaron Gassmann Laboratory

Research Projects

1. Resistance to Bt corn by western corn rootworm

Commercial cultivation of Bt crops began in 1996 and has provided many benefits to farmers and the agricultural community including effective management of key pests and reduced use of conventional insecticides.  In 2012, Bt crops covered over 69 million hectares (170 million acres) worldwide.  Most of this area was planted to Bt corn and Bt cotton.  In Iowa, over 75% of the corn planted in 2012 produced at least one Bt toxin.  The widespread use of this technology places intense selection on pest populations to evolve Bt resistance.  Western corn rootworm is a key pest of corn in North America and is currently managed by planting of Bt corn.  In 2009, western corn rootworm populations in Iowa began developing resistance to Bt corn and this resistance has since developed in other states.  We study the evolution of Bt resistance by western corn rootworm and how knowledge of population genetics, agricultural practices and ecology may be applied to manage resistance.  Our research includes experiments in the laboratory and in farmers’ fields.  In the laboratory, we quantify the inheritance of resistance traits, the genetic variation for resistance, the response to selection for Bt resistance, and cross-resistance among Bt toxins.  We visit farmers’ fields to measure injury to Bt corn by western corn rootworm and then conduct laboratory experiments to measure the level of resistance for these field-collected populations.  Through on-farm studies, we are testing how resistance affects pest injury to Bt corn, survival of western corn rootworm and yield.

Beetles on leafHealthy vs. Injured rootsGreenhouse plants

2. Fitness costs of Bt resistance in agricultural pest insects  

The refuge strategy delays pest resistance to Bt crops by providing a refuge of non-Bt crops that enable the survival of Bt-susceptible individuals. Because of these delays in resistance, the US EPA mandates the planting of non-Bt refuges. Fitness costs of Bt resistance occur in the absence of Bt when resistant individuals have lower fitness than Bt-susceptible individuals. Fitness costs remove resistance alleles from the refuge population and increase the delays in Bt resistance achieved through the refuge strategy. Moreover, ecological factors such as host-plant varieties and entomopathogens can magnify fitness costs. Our research is focused on identifying ecological factors that increase fitness costs of Bt resistance and understanding the population-level consequences of these effects. Research in this area includes three major insect pests that are managed with Bt crops: European corn borer, pink bollworm and western corn rootworm.

nematodesWCR GreenhouseNematodes in Petri dishes compared to a quarter

3. Integrated pest management for corn and agro-ecology of corn cropping systems

The goal of integrated pest management (IPM) is to apply multiple methods to manage pests in a manner that maximizes profits for farmers and preserves environmental quality.  We study both current and future management tools available for corn rootworm, and test agriculturally relevant ecological hypotheses about the efficacy and compatibility of various IPM tactics.  Through this research, we aim to generate fundamental knowledge that will improve agricultural practices in the long term, and provide unbiased information for growers to apply in the near term when making management decisions for their farms.  As part of our IPM research, we conduct a field evaluation program that tests current and pre-commercial insecticides and Bt crops for management of western corn rootworm and other pests of corn.  Research on IPM also includes: the benefits of crop rotation and cover crops for managing pests in corn, effects of host-plant resistance traits on the broader pest community, costs and benefits of combining conventional insecticides with Bt crops, and broad-scale spatial patterns in pest abundance.  Additionally, we are characterizing the community of entomopathogens (i.e., insect killing pathogens) found within cornfields, and testing 1) effects of current agricultural practices on the abundance and diversity of entomopathogens, 2) tritrophic interactions among western corn rootworm, corn and entomopathogens, and 3) potential for entomopathogens to enhance management of corn rootworm.

Corn fieldtents in a fieldcorn emergence cage