Sequential sampling plan of greenbug, Schizaphis graminum (Hemiptera: Aphididae) in wheat fields
عنوان دوره: دومین کنگره بین المللی حشره شناسی ایران
نویسندگان
چکیده
Sequential sampling plans of greenbug, Schizaphis graminum Rondani were developed in wheat fields of Varamin region, Iran. Aphid population was sampled weekly during two growing seasons of 2011-2012. Sampling was done from immigration of aphids to wheat fields at tillering stage in late March to harvesting time in middle of June. In this research a big sample (>30 samples) was used and 50 wheat stems were chosen randomly at each sampling date in a zigzag sampling plan. Infested parts of each wheat stem were placed in a tube and the number of S. graminum nymphs and adults was counted using a stereomicroscope. The data obtained were used to describe spatial distribution pattern of S. graminum by Taylor’s power law and Iwao’s patchiness regression methods. Aphid population varied from 0.02 to 4.62 aphids per wheat stem. Results indicated aggregated dispersion pattern of greenbug population in wheat fields using two methods, but Taylor’s power law (r2 = 0.973) provided a better description of the aphid’s spatial distribution than Iwao’s method (r2 = 0.666) based on the regression coefficients. Estimates of spatial distribution plan were used to develop sequential sampling plans and sampling stop lines using Green (1970) method at precision levels of D = 0.1 and D = 0.25. Based on the results, sample size required to estimate greenbug mean population using the obtained sequential sampling plans was reduced by increasing aphid population. In the model at D = 0.25 precision level, sample size was 106 stems at mean population of 1 aphid per stem, but it decreased to 56 stems at the highest aphid density observed in the wheat field (4.62 aphids per stem). Also, sample size required to estimate mean aphid density increased more than 6th times by decreasing precision level from 0.25 to 0.1. For example, at mean density of 1 aphid per stem, 667 stems should be counted for sampling at D = 0.1 precision level, but sample size required was decreased to 106 stems using the model with D = 0.25 precision level. In conclusion, very large sample sizes was required in sampling at D = 0.1 precision level and the model at D = 0.25 precision level is recommended for sampling greenbug population.
کلیدواژه ها