Sequential sampling of overwintered sunn pest, Eurygaster integriceps (Het.: Scutelleridae) in rainfed wheat fields in Borujerd, Iran

The sunn pest, Eurygaster integriceps Puton, is the most important pest of wheat and barley in most wheat producing regions of Iran, including Lorestan province. The pest overwinters under bushes in mountains and returns to wheat fields in the next spring. Study of spatial distribution of overwintered sunn pest (OSP) in rainfed wheat fields using two quadrate sizes (50 × 50 cm2 = 0.25 m2 and 70.71 × 70.71 cm2 = 0.5 m2) and their conformity with negative binomial distribution, showed a dispersion pattern of aggregation. In this study, a sequential sampling plan (Wald’s method) was presented by use of 1.5 OSP/m2 as an action threshold and 1.05 OSP/m2 as the safety level, and estimating the common K (Kc) for the both sizes of quadrates in 2004 and 2005. Two sizes of quadrates were used as sample units to estimate densities and dispersion patterns of the pest populations. The decision lines, y = 0.32x ± 7.62 and y = 0.63x ± 7.44 were calculated for 0.25 and 0.5 m2 quadrates, respectively. The operating characteristic (OC) and average sample number (ASN) curves indicated that low numbers of samples are required for control decision making when the population densities are either low (less than 0.22 and 0.44 OSP/q for small and large quadrates, respectively) or high (more than 0.45 and 0.89 OSP/q for small and large quadrates, respectively). However, the number of samples required will be high when the population density is nearly medium and at the point of inflection of OC curve (0.32 and 0.63 OSP/q for small and large quadrates, respectively).