Estimation of Mole Cricket Populations

It is difficult to estimate the size of mole cricket populations per unit area (e.g., numbers per acre) because these insects live underground, so cannot readily be seen and counted. They can be dug out manually with a shovel, or mechanically with a tree spade or a soil-coring device operated from a tractor. The soil extracted per square yard (or other relatively small unit of area or volume) can then be sifted for mole crickets. However, mole crickets tend to be distributed unevenly, so that samples have to be taken at many places per given acre, and the number of mole crickets per sample has to be averaged. This kind of sampling is highly labor-intensive, and the digging required will make manicured turf look unsightly.

A less disruptive method of extracting mole crickets from soil is to pour diluted liquid detergent onto the soil surface. The detergent will then soak into the ground and cause mole crickets to come to the surface, where they will die. An appropriate mixture is 1.5 fluid ounces of liquid dish washing soap in 2 gallons of water poured over an area of 4 square feet. A lightweight square portable frame called a quadrant delineates the area of 4 square feet over which the liquid is poured. Mole crickets present will rise to the surface within about 2 minutes. No damage to turf has been observed with any of several liquid detergents that have been tested. The effectiveness of this method will vary according to the moisture level of the soil, but in repeated comparisons it seems no less accurate than digging mole crickets from the soil. Estimates of numbers of mole crickets per unit area obviously are good only for the time and place on which they were taken.

Indirect estimates of mole cricket numbers can be made using a quadrant subdivided by strings into smaller squares. The numbers of smaller squares showing mole cricket galleries, or showing incomplete grass coverage of the surface (provided that you can be sure that loss of coverage was due to mole cricket activity), are indicators of mole cricket activity. These indicators relate in imprecise ways to the numbers of mole crickets that were present at some time in the past in the unit area sampled.

Two sorts of traps have been devised for mole crickets: pitfall traps and flight traps. Basic pitfall traps are buckets or other containers sunken into the ground until the rim is level with the soil surface. In warm, humid weather, mole crickets tend to come to the soil surface to move about; any that cross the rim of the bucket are likely to fall in and be trapped. Other insects, too, can be captured in pitfall traps. More elaborate pitfall traps can use plastic or metal gutters with rims level with the soil surface, and these gutters leading through holes in the sides of a partially buried bucket with a lid; trapped insects make their way into the bucket. Flight traps can be used to capture winged, adult mole crickets. These traps rely on something that is attractive to the mole crickets. The two major attractants are mole cricket song and light. The attractant is suspended over a large metal or fiberglass funnel leading downward to a container such as a bucket of soil, in which the trapped mole crickets are collected. Mole crickets are clumsy in flight, and will not necessarily land in a flight trap: a large proportion of them may land around it.

The number of mole crickets caught in pitfall traps and flight traps depends not only upon the number of mole crickets in the vicinity of the traps, but also on their activity level. Activity levels depend upon physiological status, which is influenced by age, time of year, time of day, temperature, moisture, nutritional status, and other factors. The catches in these traps do not relate to any specific unit area, so they cannot be used to estimate the number of mole crickets per acre — they are used to collect mole crickets for experimental purposes. They were not designed as methods of controlling mole crickets, and there is no evidence that they reduce mole cricket populations even when operated constantly for years.

The number of mole crickets caught in flight traps, using song as the attractant and operated constantly, has varied from year to year at trapping stations near Gainesville and at Bradenton. These trapping stations have been operated for more than 16 years at each location. Variation in numbers of mole crickets trapped from year to year bears no obvious relationship to total annual rainfall or to minimum winter temperatures. Only since establishment of biological control agents near these stations has the number of mole crickets trapped shown a decline.

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