(Hyperlinks exist in all of the maps on this page.)

The *Outbreak Frequency Map* is an historical (1944 - 1996) summary
of infestations >= 8 grasshoppers/yd^{2}. This map highlights areas that
have frequently suffered from grasshopper outbreaks.

This map depicts the probability of a grasshopper infestation persisting and answers the question, "If the rangeland was infested last year, what is the probability that it will be infested this year?".

This map depicts the expected duration that a site is likely to be infested and answers the question, "If the rangeland is infested at present, how long will this condition likely continue?".

This map depicts the probability of a grasshopper infestation developing
and answers the question, "If the rangeland was **not** infested last
year, what is the probability that it will be infested this year?".

This map depicts the expected duration that a site is likely to be uninfested and
answers the question, "If the rangeland is **not** infested at present,
how long will this condition likely continue?".

## Survey:

The key to effective pest management is to focus the search for rangeland grasshoppers on those lands most likely to be infested.

Therefore, based on what you know of last year's situation, the most effective strategy would be to survey: 1) areas that were infested and have a high probability of continuing infestation and 2) areas that were uninfested and have a high probability of becoming infested.## Control:

It may be necessary to focus management programs in areas that have the greatest potential for economic return. One of the most important elements of assuring a profitable treatment is to control populations that are likely to persist if nothing is done, thereby accruing multiple-year benefits from this year's treatment. Conversely, if an infestation has a low probability of persisting beyond the current year, then the economic returns from a control program will be limited to the forage that is protected in a single growing season.

Therefore, with all other factors being equal, management priority should be allocated to land that has the longest expected duration of infestation and the greatest probability of continued infestation.

As with financial investments, past performance is no guarantee of future returns. In an ecological sense, our analysis assumes that all of the factors that were responsible for grasshopper population dynamics over the last 50 years are continuing to operate in the same manner at the present time. Any changes in the inputs that accounted for the transitions in the past will affect the accuracy of our current forecast.

The only grasshopper population density that was consistently recorded since 1944 is > 8 grasshoppers/yd

^{2}. We know that this density rarely represents the economic threshold, although it may be close to the ecological carrying capacity of the rangeland, and it may portend an increase in the population. However, all of the probabilities and durations reflect this particular density. So, for example, the chances of an infestation of 25 grasshoppers/yd^{2}persisting for more than a single year may be much different than the probability indicated on these maps.Our analysis was conducted using a spatial unit of 250 acres. That is, each of the grid "cells" on the map represents a fixed area of rangeland, and it is possible that the analysis would have yielded a different results is a substantially larger or smaller scale had been used. However, we chose a parcel size of 250 acres as being small enough to provide an appropriate level of detail but large enough to be of relevance to management practices.

Terms:

Infested = 8 grasshoppers/yd

Uninfested = < 8 grasshoppers/yd

To get a Free Viewer for Shape Files download ArcExplorer and an Unzip Utility download WinZip.

For more maps and an in-depth discussion on the ArcView Two-State Markov Chain Extension.

Copyright 2000 Kiana Zimmerman, Jeffrey Lockwood, and Scott Schell.

Entomology Section

Department of Renewable Resources

College of Agriculture

University of Wyoming

Most recent update: 11/01/10