Grasshoppers

Grasshopper Life Cycle and Seasonal Behavior

There are over 100 different species of grasshoppers documented in Wyoming. Grasshopper pest species overwinter as eggs deposited in the soil. In late spring and early summer, these eggs hatch and grasshoppers begin developing through several immature stages, called instars, before reaching adulthood later in the season. Weather conditions, soil moisture, and temperature all influence hatch timing and population success from year to year.

Grasshopper management efforts focus on the early stages of development, when grasshoppers are small and actively growing. Treating populations during this period allows impacts to be reduced before grasshoppers mature, disperse more widely, and become more difficult to control. Monitoring life cycle stages helps determine when management actions may be appropriate and when treatment is unlikely to be effective.

Grasshopper outbreaks in Wyoming are not the same as locust swarms described in other parts of the world. Management efforts are intended to address localized population increases and reduce impacts, not to eliminate grasshoppers from the landscape.

According to APHIS, grasshoppers are not considered to be a hazard this year.

2026 Grasshopper Hazard Map
2025 Program Summary

For more information please visit: the USDA Animal and Plant Health Inspection Service of Wyoming

Program Participation and Assessment

Landowners interested in grasshopper treatment must visit the Platte County Weed and Pest District office to map their intended treatment area. During years when emergency insect management programs are in place, mapping is conducted by appointment only.Once mapping is complete, the proposed treatment area will be evaluated and monitored. Site conditions, grasshopper activity, timing, and population levels are assessed to determine whether treatment is appropriate.Mapping and assessment do not guarantee treatment. Decisions are based on monitoring data, program guidelines, and current conditions.While many grasshopper species are present in Wyoming, a small number are considered economically destructive and are the primary focus of monitoring and management efforts.

How Dimilin Works and Why Timing Matters

At Platte County Weed and Pest District, Dimilin is used as part of our grasshopper monitoring and management efforts. Dimilin is an insect growth regulator that affects immature grasshoppers by interfering with the molting process, which prevents them from developing into adults. Dimilin is effective only during early life stages and does not affect adult grasshoppers, making application timing a critical component of successful control.

Grasshopper monitoring typically occurs in late spring and early summer, when grasshoppers begin to hatch and develop. Treatments are targeted during this period, while grasshoppers are still small and actively growing. Applying Dimilin during this window allows populations to be reduced before grasshoppers reach adulthood and before potential impacts to rangeland, crops, and forage become critical.

When treatments are conducted, Dimilin is applied by aerial application using fixed-wing aircraft, helicopters, or ground crews. Treatments are carried out using a RAATs approach, leaving alternating untreated strips between treated areas. This method reduces overall product use while still providing effective control, as grasshoppers move between treated and untreated areas. Application timing and methods are determined based on monitoring data, site conditions, and program guidelines.

Grasshopper treatments are intended to reduce impacts during years of elevated populations; however, effectiveness cannot be guaranteed. Results may vary based on timing, weather conditions, grasshopper species present, and population density. The Platte County Weed and Pest offers a standard cost-share of 50 percent for grasshopper treatments. During years when grasshopper populations are identified as a concern, the district may also seek separate emergency insect management funding to further assist landowners with treatment costs. Grasshopper management efforts are not intended to eradicate grasshoppers. The goal of treatment is damage control during periods of increased activity, with the intent of reducing impacts while allowing a reduced population to remain part of the local ecosystem. Applying less chemical utilizing the Reduced Agent and Area Treatments (RAATs) approach and timing the application to early morning reduces the risk to pollinators and non-target species.

History of Dimilin Use in Grasshopper Management

Dimilin, also known by its active ingredient diflubenzuron, was developed in the 1970s as an insect growth regulator and has been used for several decades in grasshopper management programs across the western United States. Unlike traditional insecticides that target adult insects, Dimilin was designed to interrupt insect development by affecting the molting process in immature insects.

Because of this mode of action, Dimilin became widely adopted for large-scale grasshopper management programs, including those administered or supported by the U.S. Department of Agriculture and the Animal and Plant Health Inspection Service. Its use allowed agencies to focus on early intervention during grasshopper development rather than relying on broad-spectrum adult control later in the season.

Over time, Dimilin has remained a commonly used tool in grasshopper management due to its effectiveness when applied at the appropriate life stage and its suitability for large rangeland treatment areas. Its use is guided by federal and state regulations, product labeling, and ongoing monitoring of grasshopper populations and environmental conditions.