Sampling of adult wheat stem sawfly (Cephus cinctus Norton) to predict larval infestation

The wheat stem sawfly (Cephus cinctus Norton) is a key pest of wheat in the Northern Great Plains. The current sampling method for this insect involves the splitting of wheat stems to record the presence of sawfly larvae. This process is time consuming and labor intensive. The plan requires the user to split, at minimum, 300 stems to check for the presence of the larvae. The processing time required is 3 ¾ hours assuming a 45 second processing time per stem. An alternative sweep net sampling plan based on the number of female sawflies captured would be faster than the current plan. Adult and larval samples were collected from three wheat fields in the Nebraska Panhandle to establish the relationship between female sawflies sampled, distance into the field, and larval infestation. This data was subsequently analyzed with regression analysis to develop equations to predict the larval infestation by the density of female sawflies. Then, using parameters generated with Taylor’s Power Law, the minimum number of samples for a desired precision level was calculated. To maintain a 20% standard error about the mean the minimum number of samples required is 7. Sample processing requires 4 minutes per sample, and thus, it would take 28 minutes to process samples for a field mean – an 88% reduction in the time required. This plan gives growers a faster tool to help them make pest management decisions concerning the sawfly.