Spatial distribution patterns of apple sawfly populations in two differently managed commercial apple orchards

Abstract

An investigation on spatial distribution of apple sawfly (Hoplocampa testudinea Klug, 1816) populations was conducted in organically and conventionally managed apple orchards of Institute of Horticulture, Lithuanian Research Centre for Agriculture and Forestry in 2010-2013. The aim of this study was to examine population density patterns of within orchard spatial distribution of apple sawfly. White sticky traps Rebell ® bianco (Andermatt Biocontrol, Switzerland) were used to monitor apple sawfly population density. In order to determine aggregation extent in sawfly populations, coefficient k of the negative binomial distribution, serving as aggregation index, was computed using maximum-likelihood method. Additionally, in order to accurately evaluate distribution patterns of apple sawfly within orchards, spatial analysis using Kernel density function was performed. Spatial analysis was performed using program package ARCGIS 10. Results of the study on spatial distribution patterns of apple sawfly imagoes demonstrated strong tendency for aggregation of adult sawflies across the orchard area. Localisation of clumps was quite constant despite the size of the orchard. Such knowledge could be applied for optimization of apple sawfly control strategies, especially in large orchards. The highest infestation levels were recorded exactly in the aggregations of sawflies over the course of the study. Moreover, knowing exact locations of such aggregations could be useful for optimization of positioning of traps in the orchards and, ultimately, restricting insecticide applications only to places where it is really necessary.