Sequential Sampling for Panicle Caterpillars (Lepidoptera: Noctuidae) in Sorghum

Abstract

Panicle caterpillars comprise an economically important insect pest complex of sorghum throughout the Great Plains of the United States, particularly in Kansas, Oklahoma, and Texas. The sorghum panicle caterpillar complex consists of larvae of two polyphagous lepidopteran species: the corn earworm, Helicoverpa zea (Boddie), and fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae). Sampling for panicle caterpillars in sorghum fields is usually accomplished by the beat bucket sampling technique with a fixed sample size of 30 beat bucket samples of one sorghum panicle each per 16.2 ha of field. We used Wald's sequential probability ratio test for a negative binomial distribution to develop a sequential sampling plan for panicle caterpillars. In total, 115 sorghum fields were sampled in Kansas, Oklahoma, and Texas from June to August 2010. Panicle caterpillars had an aggregated distribution of counts confirmed by Pearson's chi-square statistic for lack of fit to the negative binomial distribution for each sampled field. A sequential sampling plan was developed using a high threshold (an economic threshold) of 0.5 caterpillars per sorghum panicle, a low threshold (a safe level) of 0.20 caterpillars per panicle, and fixed error rates (alpha = 0.10 and beta = 0.05). At caterpillar densities > 0.45 and < 0.12 per panicle, the average number of panicles inspected to make a decision was less than the current recommendation of 30. In a 2013 validation test of 25 fields, the expected number of samples taken from average sample number curve was in close agreement with the number of samples required using the sequential plan (r2 = 0.93), and all fields were correctly classified when compared with a fixed sample size result. The plan improved upon current sampling recommendations for panicle caterpillars in sorghum because at known acceptable fixed error rates fewer samples were required when caterpillars are scarce or abundant, whereas more samples were required to make decisions with the same acceptable error rates when densities were near the economic thresholds.

Spatial distribution and sequential sampling protocol for Spodoptera frugiperda (Lepidoptera: Noctuidae) on commercial maize fields in Sinaloa, Mexico

“…In addition, to estimate the maximum and minimum density limits to stop sampling, the Kumo model was used, while the Green model was obtained to define the maximum number of sampling units, using a control threshold of 40%. Elliott et al (2014), developed a sequential sampling plan for Helicoverpa zea (Boddie), corn earworm, and fall armyworm as a complex in sorghum. They used the TPL model to estimate the distribution pattern of the larvae and applied the Wald method for the elaboration of the sequential sampling plan with a maximum level of 0.5 larvae per panicle and a low level of 0.2.…”

“…On the other hand, Elliott et al (2014) According to Bolvin and Vincent (1983), the following four elements are needed to develop a sequential sampling plan: a) A practical and reliable sampling procedure; b) The economic threshold of the organism in a specific crop; c) The parameters of a mathematical model that describes the spatial distribution of the sampled organism; d) Realistic and acceptable levels of error to estimate pest populations in crops.…”

Feeding preference of Spodoptera frugiperda on different sorghum genotypes

“…Even with these characteristics, some relevant factors have caused significant damage to their production, as pests (ELLIOT et al, 2014). The fall armyworm, of the genus Spodoptera is one of the pests that cause significant damage, it is widely distributed in the world, causing significant damage, and among the 30 species described, half are pests of sorghum and several crops of economic importance.…”

A Web-based Decision Support System for Managing Panicle Caterpillars in Sorghum

“…Thus, excessive time is spent sampling when a very low or high density of pests is present. We recently developed a sequential sampling procedure (Elliott et al, 2014) based on the beat bucket sampling method described in Cronholm et al (2007) that overcomes the problems outlined above. The sequential sampling procedure will aid growers in making time‐ and cost‐effective decisions for managing panicle caterpillars.…”

“…Sequential sampling overcomes the limitations described above for fixed sample size techniques (Binns, 1994) and can result in a 50% or greater reduction in the time required to sample a sorghum field (Binns, 1994). The sequential sampling procedure developed by Elliott et al (2014) improves on current sampling recommendations for panicle caterpillars in sorghum. At known acceptable fixed error rates, up to 44% fewer samples were required when caterpillars were scarce or very abundant.…”