Mormon cricket control in Utah ’s West Desert: impacts on non-target arthropod communities and implications for vertebrate species at risk

Project Number: 9398-BNPRA
Cooperating Agencies: US Department of Agriculture, Bureau of Land Management
Project Chief: Tim B. Graham, USGS Moab, Utah
Project Period: 2004-2006

Problem: In rangeland ecosystems of the United States, such as Utah’s West Desert, Orthoptera populations, particularly grasshoppers and Mormon crickets, can propagate to levels that can be economically damaging to land owners. The U.S. Department of Agriculture Animal and Plant Health Inspection Service (APHIS) conduct surveys on grasshopper and cricket populations and provide technical assistance to land owners for proper management. When direct intervention is requested by a Federal land management agency or a State agricultural department, APHIS responds by applying insecticide within all or part of the outbreak area in an effort to rapidly suppress or reduce grasshopper populations and effectively protect rangeland. In the last 5-6 years, grasshopper and Mormon cricket populations have increased substantially due to drought conditions. Since 2002, control efforts have been implemented in certain areas. The primary chemicals used for insect control are carbaryl (applied as bran bait), and dimilin or diflubenzuron (applied as an aerial spray).

Objectives: Principal study objectives are ( 1) to compare terrestrial and aquatic arthropod community structure (abundance and species composition) in treated and untreated sites in the West Desert and Utah Valley to determine if response is similar across the landscape and (2) to compare terrestrial and aquatic arthropod community structure over time to determine whether these communities restore themselves, and at what rate, following insecticide treatment.

Relevance and Benefits: The US Fish and Wildlife Service and Utah Division of Wildlife Resources developed conservation plans for two vertebrate species, the Columbia spotted frog and the Utah Sage-Grouse that reside in the West Desert and Utah Valley. The conservation plans were developed to keep the species off of the threatened and endangered list. The occurrence of insecticide may jeopardize the success of these conservation plans by endangering these species through direct contact or through the food chain. Information on the topic will contribute to a more comprehensive conservation plan.

Approach: This project aims to monitor acute and chronic impacts of insecticide treatment on invertebrate communities by sampling in selected areas of the west desert (1) before treatment (2) immediately (within 2 weeks) following application (3) following leaf fall or a major rain event that could potentially release additional carbaryl or dimilin (that remained on the riparian vegetation following initial application) into aquatic systems, and (4) yearly follow-up to assess community restoration.

Products: An administrative report will be prepared and presented to the BLM and APHIS, detailing results of arthropod sampling and analysis. The report will assess changes in arthropod communities in relation to published literature about sensitive vertebrate species such as spotted frog and western sage-grouse, and make recommendations for additional research, suggested management approaches, and monitoring protocols based on project findings. In addition, if the data warrant, manuscripts to peer-reviewed journals will be prepared.

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