The influence of management practice on the spatial distribution of Lepidopteran pests in Brassica crops in the Democratic People's Republic of Korea: implications for sequential sampling plans

Abstract

Plutella xylostella and Pieris rapae are the key components of a pest complex that attacks Brassica crops in the Democratic People's Republic of Korea (DPRK). We examined the spatial distributions of these insects within crops both as individual species and when combined as a standard insect that was derived from their relative feeding rates. The influence of standard co-operative management practice and an integrated pest management (IPM) strategy on the dispersion of the standard insect was tested. Iwao's m* -m relation was then used to describe the distribution of standard insects by management categories and of Pieris rapae using all data. Pest management practices only affected the distribution of the species when they were combined into standard insects. Enumerative sampling plans were therefore designed for standard insects based on population data derived from IPM-managed fields and for Pieris rapae from population data from all experimental fields. The presented plans have the potential to make a significant contribution to managing lepidopteran pests in the DPRK. The approach will be useful in the design of sequential sampling plans for other geographical regions where these pests co-occur and can also contribute to the development of sequential sampling plans for other pest complexes for which standard insects can be derived.

Iwao's patchiness regression through the origin: biological importance and efficiency of sampling applications

“…Despite sound mathematical and biological arguments for using a through-origin version of Iwao's m * -m relation, the effect of using regression through the origin on applications of the model would need to be considered before such an approach could be advocated. The most common application of Iwao's m * -m relation is the design of sequential sampling plans based on Kuno's method (Kuno 1969;Jones and Parrella 1984;Allsopp and Bull 1989;Pena and Baranowski 1990;Waters et al 2009).…”

“…where SD is the standard deviation in sample estimate of m x ðÞand n is the number (n) of sampling units collected (Kuno 1969;Waters et al 2009). Normally, D ¼ 0:3i s used as a standard for the fixed level of precision (Barney and Legg 1988;Hutchison et al 1988;Garat et al 1999;Shah et al 2000;Waters et al 2009). The minimum sample size required to estimate density is given by the formula (Kuno 1969):…”

“…When the cumulative tally of target organisms collected is greater than the value at the stop line, sampling is terminated (Kuno 1969;Waters et al 2009).…”

“…on plants in a Danish field trial. It has been suggested that model II regression be used for estimating the parameters of Iwao's m * -m relation (Waters et al 2009). Model II regression is often recommended when the Fig.…”

“…For each intercept value a, two lines are presented; the upper has slope b = 1.1 and the lower slope b = 2.0. D = 0.3 Popul Ecol (2014) 56: 393-399 395 independent variable is subject to error, (Patil and Stiteler 1973;Sokal and Rohlf 1995) as with x in Iwao's Patchiness Regression (Waters et al 2009). However, in this paper we used ordinary least squares regression as recommended by Legendre (1998) since our data did not meet the bivariate normality assumption of model II regression.…”