The impact of dimethoate on the spatial distribution of beneficial arthropods in winter wheat

Abstract

The within-field spatial distribution of beneficial arthropods was assessed using two-dimensional grids of pitfall traps and suction sampling across two winter wheat fields of 4 and 16 ha, before and after an application of dimethoate. An unsprayed 6 m wide buffer zone was left around half the edge of the larger field. Arthropod numbers fluctuated to varying extents prior to spraying. Two species of Carabidae (Pterostichus madidus and I? melanarius), Linyphiidae, Lycosidae and Aphidius spp. (Braconidae) all showed their greatest reduction after spraying. For five carabid taxa, Tachyporus spp. (Staphylinidae) andCollembola the decline in numbers following spraying was no greater than any reduction found during the pre-spraying period. Within field spatial distributions of three arthropod groups were analysed using SADIE. I? madidus, present in patches across the centre of both fields prior to spraying, was removed by dimethoate and by 34 days after spraying had recovered most at the field edges. Linyphiidae were evenly distributed across both fields prior to spraying. Their numbers were reduced considerably by dimethoate and they did not recover to pre-spray levels. However, where recovery occurred this was across the centre of both fields indicating their potential to reinvade whole fields. Aphidius species were also evenly distributed across both fields prior to spraying, but did not recover after spraying. Some, but not all arthropods survived within the unsprayed buffer zone and there was some indication that reinvasion of the mid-field was more extensive where this was present. The importance of field margins with respect to insecticide treatments is discussed. invertebrate ecology of farmland as a mirror of the intensity of the impact of man?-an approach to interpreting results of field experiments carried out in different crop management intensities of a sugar beet and an oil seed rape rotation including set-aside. Biological Agriculture and Horticulture 15:83-108.

Conversion of single-layered Scots pine monocultures into close-to-nature mixed hardwood forests: effects on parasitoid wasps as pest antagonists

“…In addition to the ecological risks linked to chemical pest control of damaging non-target organisms (Croft and Theiling 1989;Butler et al 1997;Paulus et al 1999;Holland et al 2000) and the evolution of insecticide resistance (Denholm et al 1999;Soderlund and Knipple 1999;Sauphanor et al 2000), insect mass infestations cause tremendous economic losses (Straw et al 2002). The causes of insect outbreaks have been discussed since plantation forestry increased in importance.…”

Bioactivity and structure–activity relationship of natural methoxylated phenylpropenes and their derivatives against Aphis craccivora Koch (Hemiptera: Aphididae)

“…The aphid control measures have largely been depending on the use of chemical pesticides including chlorinated hydrocarbons, organophosphates, carbamates (Shetlar 2001), which besides causing resistant development in the target population (Hollingsworth 1994;Han and Li 2004) aVect adversely the natural enemies of aphids in the Weld (Holland et al 2000;Jansen 2000). In addition, increasing documentation of negative environmental and health impact of synthetic insecticides and increasingly stringent environmental regulation of pesticides (Isman 2000) have resulted in renewed interest in the development and use of botanical pest management products for controlling aphid pest.…”

Quantifying the impact of environmental factors on arthropod communities in agricultural landscapes across organizational levels and spatial scales

“…This may be a consequence of both pesticide tolerance and high recolonization ability according to dispersal ability or reproduction. Large arthropods were highly dominated by carabid beetles, some of which appear to be comparatively tolerant to pesticide application (Holland, Winder & Perry 2000), whereas small-bodied species may take advantage of fast reproduction rates after population declines caused by frequent disturbances (Peters 1986).…”