No significant effects of insecticide use indicators and landscape variables on biocontrol in field margins

L Bakker,W Van Der Werf,F.J.J.A Bianchi

doi:10.1016/j.agee.2020.107253

L Bakker, W Van Der Werf + Show 1 more

Open Access

https://doi.org/10.1016/j.agee.2020.107253

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Abstract

Insecticides are used widely to manage pests, but they may cause mortality in natural enemy populations and non-target prey. On the other hand, resources provided by the landscape – often associated with semi-natural habitat – may enhance natural enemy communities. While there is substantial information on how insecticide use and semi-natural habitats influence biocontrol in crop fields, little is known about how local insecticide use interacts with landscape variables to govern natural biocontrol in field margins. In this 2-year study we assessed predation and parasitism rates of eggs of the cabbage moth (Mamestra brassicae) on potted cabbage plants in field margins adjacent to 20 organically managed fields and 18 conventionally managed fields We analysed egg predation and parasitism rates in field margins using three predictors for insecticide use: (i) farming system (organic or conventional), (ii) frequency of insecticide use in the adjacent focal fields, and (iii) estimated insecticide use quantity within a radius of 1 km from the sampling sites. Insecticide use included foliar or soil-applied applications, including mineral oils. Landscape variables were used as covariables to account for landscape effects. Mean predation and parasitism rates were 14 % and 6%, respectively. There were no significant associations between predation and parasitism rates in field margins with insecticide use in the adjacent field or the wider landscape. Our findings suggest that field margins can be valuable habitats for natural enemies in agricultural landscapes, irrespective of the insecticide use intensity at the local and landscape scale.

Highlights

Agricultural intensification has been associated with declines in biodiversity and regulating ecosystem services (Kleijn et al, 2019)
While we have a fairly good un derstanding of how insecticide use and semi-natural habitat influence biocontrol in crop fields, little is known about how local insecticide use interacts with landscape variables to govern natural biocontrol in field margins
We study whether the proportion of semi-natural habitats in the surrounding landscapes counteracts potential impacts of insecti cide use on the biocontrol potential of natural enemies in field margins

Summary

Introduction

Agricultural intensification has been associated with declines in biodiversity and regulating ecosystem services (Kleijn et al, 2019). In diversified landscapes with high levels of natural enemy activity, insecticide-treated areas may be readily recolonized by natural enemies from source habitats once the insecticide residue has declined (EFSA Scientific Committee, 2016; Schellhorn et al, 2014; Spromberg et al, 1998). In these cases, spill-over of natural enemy populations from semi-natural habitats to agricultural fields may counterbalance non-target impacts of insecticides on natural enemies in fields (Roubos et al, 2014; Tscharntke et al, 2016). Whereas spill-over effects of natural enemy populations from field margins to agricultural fields have been relatively well studied (e.g. Dainese et al, 2017; Holzschuh et al, 2007; McHugh et al, 2020; Woodcock et al, 2016a), the impacts of insecticides on ecosystem services in field mar gins have received little attention

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