Interactions between conventional and organic farming for biocontrol services across the landscape

Abstract

While the area of organic crop production increases at a global scale, the potential interactions between pest management in organic and conventionally managed systems have so far received little attention. Here, we evaluate the landscape-level codependence of insecticide-based and natural enemy-based pest management using a simulation model for parasitoid-host interactions in landscapes consisting of conventionally and organically managed fields. In our simulations conventional management consists of broad-spectrum or selective insecticide application, while organic management involves no insecticides. Simulations indicate that insecticide use can easily result in lose-lose scenarios whereby both organically and conventionally managed fields suffer from increased pest loads as compared to a scenario where no insecticides are used, but that under some conditions insecticide use can be compatible with biocontrol. Simulations also suggest that the pathway to achieve the insecticide reduction without triggering additional pest pressure is not straightforward, because increasing the proportion of organically managed fields or reducing the spray frequency in conventional fields can potentially give rise to dramatic increases in pest load. The disruptive effect of insecticide use, however, can be mitigated by spatially clustering organic fields and using selective insecticides, although the effectiveness of this mitigation depends on the behavioral traits of the biocontrol agents. Poorly dispersing parasitoids and parasitoids with high attack rates required a lower amount of organically managed fields for effective pest suppression. Our findings show that the transition from a landscape dominated by conventionally managed crops to organic management has potential pitfalls; intermediate levels of organic management may lead to higher pest burdens than either low or high adoption of organic management.

Organic fields sustain weed metacommunity dynamics in farmland landscapes

“…However, due to lower yields, larger surfaces are needed to maintain food production under OF, hence the net balance between positive and negative impacts is still debated [12,15,16]. OF effects at the field level may further depend on surrounding landscapes [4,17,18]. Bengtsson et al [19] proposed that OF benefits on biodiversity should increase linearly with agriculture intensification at the landscape scale.…”

Intersection between biodiversity conservation, agroecology, and ecosystem services

“…Furthermore, these authors determined that these effects were due to insecticides by also comparing treated and untreated conventional fields and finding that like organic farms, insecticide-untreated fields had higher predator-prey ratios than insecticide-treated fields. Moreover, effects of insecticide input on bio-control can go beyond farm level (Bianchi, Ives, and Schellhorn 2013). For example, crop pest abundance increases with the proportion of harvested cropland treated with insecticides in Midwestern United States (Meehan et al 2011), although this relationship can vary greatly between years (Larsen 2013).…”

“…Though classified as 'simple' due to high amounts of cropland, a closer evaluation showed that biodiversity enhancement was mainly driven by the amount of cropland under organic management. Likewise, a simulation study found that a minimum proportion of organically managed farms in the landscape was needed to sustain parasitoid populations and to provide biocontrol services (Bianchi, Ives, and Schellhorn 2013). Furthermore, landscapes with a high amount of cropland, but also with heterogeneous crop management, may result in attenuation of negative interactions among natural enemies, allow coexistence, and increase regional diversity.…”

“…For example, Chaplin-Kramer et al (2011) found that natural enemies positively respond to landscape context but that the scale at which natural enemies respond to this landscape metric depends on degree of specialization. Accordingly, the strength and direction of landscape quality effects on parasitism rates are contingent on parasitoid traits such as search behavior and dispersal ability (Bianchi, Ives, and Schellhorn 2013). This is complicated by the fact that the scale of these responses can greatly vary from species to species depending on their dispersal capabilities and even closely related species often lumped into the same functional group can perceive landscape fragmentation differently (Doak, Marino, and Kareiva 1992;Gardiner et al 2009b;With and Crist 1995;With et al 2002).…”

Impact of Organic Farming on Biodiversity

“…conventionally managed systems have to date received little attention [38]. Organic agriculture improves biodiversity at the field level, but potential interactions with the surrounding landscape and the potential effects on ecosystem services are less well known.…”