sequential sampling

Chickpea pod borer, Heliothis viriplaca, is an important pest of rain-fed chickpea (Cicer arietinum L.) fields in most regions of Iran. During 2017-2018, spatial distribution and fixed precision sequential sampling plans of, H. viriplaca population were investigated in rain-fed chickpea fields in Lorestan provinces. Regarding to the fitting of data with Taylor's power law and Iwao’s patchiness, parameters of these methods were used to develop of enumerative sequential sampling plans for each region. Results showed that, Taylor's b and Iwao’s β were significantly>1, indicating that H. viriplaca populations were aggregated in Lorestan provinces. Sample size curves were calculated and compared at 10%, 15% and 25% levels of precision. Validation results of Green's and Kuno’s models showed that, to achive a precision of 0.25, which is generally accepted in IPM programs, it is necessary to take samples with an average sample number (ASN) of 58 and 66 samples for green’s and kuno’s models, respectively.

Spatial distribution of the English grain aphid, Sitobion avenae (F.), was studied in wheat fields of Mahidasht, Kermanshah province and Sequential sampling models with fixed precision level were prepared for its monitoring. Sampling was conducted during five years. At each sampling date, 100 tillers were randomly visited. The mean range of population density in wheat field was 0.39-34.01 aphids/ tiller. Taylor's Power Law parameters were used to preparing sampling models according to Green (1970). Spatial distribution was determined as cumulative. Sample size decreased with increasing aphid population density in sampling models. In research precision level of (0.1), the sample size required at the highest average population density observed in the field (34.01/ tiller) was 136, which in precision level proposed for integrated pest management (0.25) reduced to 22 tillers. Overall, due to the large sample size at the precision level of 0.1, the model prepared at the precision level of integrated pest management (0.25) was recommended for monitoring S. avenae. The recommended model can reduce sample size more than six times at different densities in comparison to the sequential sampling model at the precision level of 0.1.

In this research, barley aphids in Mahidasht region of Kermanshah province were identified. Spatial distribution type and statistics for corn leaf aphid, Rhopalosiphum maidis (Fitch) were also studied and sequential sampling models were developed. Regular weekly sampling was carried out in 2015, 2016 and 2017. Each sampling date, 100 tillers were randomly visited and aphids were transferred to the laboratory for counting and identification. Taylor’s power law was used to determine spatial distribution type and statistics and sequential sampling models were developed according to Green (1970). Results revealed feeding of five species of aphids on barley including greenbug, Schizaphia graminum, rose-grain aphid, Metopolophium dirhodum, the English grain aphid, Sitobion avenae,corn leaf aphid, R. maidis and bird cherry-oat aphid, R. padi. Corn leaf aphid was more abundant during the season with 93.8%, 94.2% and 93.2% of aphids collected in 2015, 2016 and 2017, respectively. Low populations density of the other four species was observed every three years. Spatial distribution type of corn leaf aphid in barley field was determined as cumulative (b = 1.45). Sample size required in models with precision levels of 0.1 and 0.25 at mean aphid densities observed in the barley field (1.02 - 44.32 aphids per tiller) was 70 -524 and 11-84 tillers, respectively. In conclusion, sequential sampling model developed at the precision level of 0.1 was evaluated time consuming due to large sample size required, but the model at pest management precision level (0.25) was recommended for monitoring leaf corn aphid in barley fields.

Two spotted spider mite, Tetranychas urticae Koch is one of the most important pests of common bean, Phaseolus vulgaris L. fields in most regions of Iran. To deploy the appropriate management of this pest, in common bean fields, we need to construct a sampling plan that allows estimate population density quickly and accurately. During 2011-2012, spatial distribution and fixed precision sequential sampling plans of T. urticae population were investigated by the use of different sample unit sizes, in common bean fields in north of Lorestan province (Borujerd, Dorud and Azna). Regarding to the fitting of data with Taylor's power law, parameters of this method were used to develop the enumerative sequential sampling plans for each sample unit. Results showed that Taylor's b was significantly greater than 1, for all the life stages, indicating that T. urticae populations were aggregated. Comparison of Taylor's b for larvae, nymphs and adults, showed no significant difference among them. Therefore, Taylor's b and α re-estimated for total number of larvae鼩ꦆ쾚盩, without separating them. Sample size curves were calculated and compared at 10%, 15% and 25% levels of precision. Also, for each sample unit, Green's fixed precision sequential sampling plans were validated using 12 independent data sets. Validation results of these models showed that to achieve a precision of 0.25, which is generally accepted in IPM programs, it is necessary to take samples with an average sample number (ASN) of 146, 102 and 86 for sample units of 2, 4 and 6, respectively. In conclusion, the developed enumerative sequential sampling plans at precision level of 25% was recommended for monitoring this pest in irrigated common bean fields.

Asian citrus psyllid, Diaphoina citri, is one of the most important pests of citrus in South of Iran, mainly because it is the vector of causal bacterium of Greening disease. In this study, adults of D. citri were sampled using yellow sticky traps (10×25 cm) at 52 citrus orchard of Kerman and Hormozgan provinces in south of Iran. Taylor’s power law and Iwao’s regression methods were used to study spatial distribution of the pest adults. Taylor’s power law and Iwao’s parameters then were used to create Green’s and Kuno’s sequential sampling models at 10 and 25 percent fixed precision levels, respectively. Results revealed that adults caught by traps had an aggregated distribution pattern based on both Taylor’s power law and Iwao methods. Green’s sequential sampling plans developed by Taylor’s parameters were more appropriate than Kuno’s ones. In obtained sequential sampling models, sample sizes were reduced and performance of plans for rapid estimation of population was increased by increasing density of Asian citrus psyllid adults. Increasing fixed precision level from 25% to 10% resulted in up to 6-7 times increasing in number of traps required to estimate population density of adults. So, sampling at 10 percent precision level is time wasting because of large sample size estimations and green’s sequential sampling model at integrated pest management precision level (25%) is recommended because of less time needed for monitoring D. citri adults.

Crowds of the false chinch bugs Nysius cymoides appear in many canola fields of the country at pod ripening stage. To develop sequential sampling plans for eggs, immature stages and adults of the bug, samples were taken during two years from a canola field in the Broojerd Agricultural Research Station. Samples were randomly collected twice a week using a 5 × 5 cm quadrat and an aspirator. Then, the specimens were carried to the lab in alcohol tubes for counting the different stages. Taylor’s power law parameters were used to create Green’s sequential sampling plans at 10, 15 and 25 percent precision levels. The results showed that sample size for eggs was larger than nymphs and adults for different levels of precision. Sample sizes were dramatically reduced by increasing population density in different sequential models. Generally, sequential sampling models at 25 percent precision level are recommended for monitoring N. cymides populations due to reducing sample sizes to less than half, compared with those at 15 percent precision level. However, the 10 percent precision level models were not applicable because of large sample size estimations.

Between 2010 and 2011, spatial distribution and fixed precision sequential sampling plans were determined for two aphids, Rhopalosiphum maidis F. and Schizaphis graminum R., in wheat fields in Badjgah countryside of Iranian Fars province. For this purpose, two fields of two hectares each were selected and sampled on weekly basis. Each sample consisted of 200 randomly selected wheat plants along with the total number of counted aphids. Based on RV, the best sample unit was four stems. This data was used to describe spatial distribution pattern of R. maidis and S. graminum by Taylor’s power law (TPL) and Iwao’s patchiness regression methods. The results indicated aggregated spatial distribution of aphid's populations in wheat fields, based on the mentioned methods. The TPL provided a better description of the aphid's spatial distribution. Since regression line slopes were not significantly different for S. graminum and R. maidis, the same Green model was proposed for both species. In this model, minimum numbers of samples were 20, 12 and 9 for precision levels of 0.15, 0.25 and 0.3, respectively. Comparing Green and conventional methods in 0.15, 0.25 and 0.3 precision levels showed that the number of required samples were reduced 77.8 ± 1.05, 78.3 ± 0.91 and 81.4 ± 0.81 percent, respectively. Based on Wilson and Room's model, when the mean populations of aphids were 1.6, 3.86 and 5.62, the proportion of infestation in the field were 0.5, 0.75 and 0.85, respectively. Therefore, by increasing the infestation percentage of the samples, the number of required samples will be reduced.

Black bean aphid، Aphis fabae Scopoli، is the most important pest of faba bean that causes economic damage on this crop. Spatial dispersion of the aphid using Taylor power law and Iwao patchiness indices was studied by weekly sampling in faba bean fields of Veis region، Ahwaz، during 2010-2012. Taylor''s power law and Iwao patchiness were used to investigate spatial dispersion of A. fabae and a resampling for validation of sampling technique (RVSP) was used to develop a Green''s fixed precision sequential sampling for this aphid population at precision levels of 0. 25 and 0. 1. Results showed that A. fabae had aggregation dispersion on faba bean and Taylor''s power law had more fitness to the obtained data. The Optimum sample size to estimate the population density of A. fabae ranged from 25 to 2 and 73 to 10 samples depending on population densities at precision levels of 0. 25 and 0. 1، respectively.