Manitoba Grasshopper Survey Protocol

 

Purpose

• Estimates of grasshopper densities in an area in late-summer (when grasshoppers are laying eggs) helps estimate the number of eggs overwintering and forecast the risk of grasshoppers being at problem levels the next growing season.

• Collecting annual survey data shows trends in grasshopper populations over a number of years.

• This forecast can be used to prepare seeding strategies for the following year, as well as to plan for cultural or chemical forms of control.

• Monitoring grasshopper numbers in late summer during routine field visits will indicate locally areas where egg laying is likely to be highest. These areas are where grasshopper hatch will likely be heaviest the next spring, and early season populations will be concentrated. 

When to Do Grasshopper Counts

Locations should be sampled when the majority of grasshoppers are in the adult stage. Adult grasshoppers have fully developed wings and can fly. Only adult grasshoppers are counted because the survey is trying to estimate the number of eggs that will be overwintering using a technique that is not too time consuming (sampling for eggs later in the fall is very time consuming). Since the adults are the reproductive stage, they are the stage that is surveyed.

To meet this requirement, sites should be surveyed between August 1st and September 1st. The survey is designed so that counts can be done during routine field visits if desired, and thus will not be too time consuming.

Where to Do Grasshopper Counts

Only roadsides or sites in the field need to be sampled, wherever grasshopper populations appear to be highest. If both field and roadside are monitored, only whichever of the two has the highest counts will be used to produce the map. Most often, highest densities will be along the roadside, but pasture and alfalfa stands may be the reverse.

How Many Locations Should be Sampled

Sample enough locations so that you have a good representation of the grasshopper populations in your area. If possible, sample at least five locations in your district.

How to Do Grasshopper Counts

1. At each location, walk approximately 50 metres and estimate the number of grasshoppers in five one-metre² areas along the 50-metre strip. Getting exact counts can be difficult, particularly if vegetation is tall or dense.  When exact counts are not possible, estimates are all that are required to forecast risk in an area.

2. Adding the five counts and dividing by five will give you your average number per metre².

3. Fill out the attached form completely. Remember to include a legal location for each site.

Tips to Make Estimating Grasshopper Densities Easier

• Estimating the Area to Sample. Before starting the counts, measure one metre² on the ground to fix the size of the unit to be assessed for grasshoppers in your mind. A meter stick can be carried as a visual tool to give perspective for a one-metre width, if needed. With experience, one can often visualize the necessary width and a meter stick may not be required.

• Counting Grasshoppers. To estimate grasshopper density, as you begin walking the 50-metre strip, focus on an area ahead of you that is about one metre². As you walk toward the metre² area, estimate the number of grasshoppers that jump or fly from the area. If grasshopper numbers are high it will not be possible to get an exact count of the number of grasshoppers that jump or fly from the area of your count as you approach it. Estimating the approximate number, or a range (ex, 20 to 30) is sometimes all that can be done. Once at the metre², count the remaining grasshoppers in the metre² . A quick and easy way to detect grasshoppers while at the metre² is to disturb the plants in the area with your feet to encourage any grasshoppers still present to jump. Repeat four more times along the 50-metre strip to get your five counts.

• Estimating High Numbers of Grasshoppers. If grasshopper numbers are very high, and estimating the number of grasshoppers per metre² is difficult, try estimating numbers in a quarter of a metre², or a foot² area. If estimating numbers in a quarter metre², multiply by four to get a metre² count; if using a foot² count, multiplying by ten will give an approximate metre² count.

• Caution: Do Not Bias Your Counts. The grasshopper counts are meant to be a representation of the average number of grasshoppers per metre² in the approximately 50-metre area you are surveying. This means that within the 50 metres, the five counts should be at random, not just where grasshoppers are clustered. The risk of having high counts that are not representative of the true number of grasshoppers per metre² on average is even greater when counting grasshoppers in areas smaller than one metre² and multiplying by four or ten (as described above). As an example, in an area with low grasshopper numbers, selectively looking for foot² areas with at least one or two grasshoppers in them to do a counts will, after doing the math, result in counts of at least ten to 20/metre² , which may be very unrepresentative of the average grasshopper density in the area. For this reason, estimating grasshopper numbers using count areas smaller than one metre² is only recommended when populations are very high and estimating numbers per metre² is very difficult.

Recording Observations

Noting the following while surveying grasshoppers will also be useful.

Fungal Pathogen of Grasshoppers

Dead grasshoppers clinging to the upper portion of the plant are an indication of a fungal pathogen, Entomophagus grylli. Note where, and the approximate density of these diseased grasshoppers if present.

Predominant Species of Grasshopper

If you are comfortable distinguishing the different species of grasshoppers, and notice while doing the counts that a particular species of grasshopper is predominant in an area, this is useful information.

Other Observations

Other observations (such as an abundance of grasshopper predators, etc.) which may influence grasshopper populations should also be noted.

What Will be Done With the Numbers and Observations You Collect

The final results will be used to produce a grasshopper forecast map for the agricultural area of Manitoba. Grasshopper counts from August will be mapped to forecast the maximum risk for the following year according to the following criteria:

For further information, contact your GO representative.