Assessing risks and benefits of floral supplements in conservation biological control

Abstract

The use of flowering field margins is often proposed as a method to support biological control in agro-ecosystems. In addition to beneficial insects, many herbivores depend on floral food as well. The indiscriminate use of flowering species in field margins can therefore lead to higher pest numbers. Based on results from field observations and laboratory experiments we assessed risks as well as benefits associated with the provision of nectar plants in field margins, using Brussels sprouts as a model system. Results show that Brussels sprouts bordered by nectar plants suitable for the cabbage white Pieris rapae L., suffered higher infestation levels by this herbivore. In contrast, nectar plants providing accessible nectar for the diamondback moth Plutella xylostella L., did not raise densities of P. xylostella larvae in the Brassica crop. Margins with Anethum graveolens L., selected on the basis of its suitability as nectar plant for parasitoids, significantly increased the number of adult Diadegma semiclausum Hellén in the crop. This didn't translate into enhanced parasitism rates, as parasitism of P. xylostella by D. semiclausum exceeded 65 % in all treatments, irrespective of the plants in the field margin. Our findings emphasize the importance of taking a multitrophic approach when choosing flowering field margin plants for biocontrol or other ecosystem services.

High effectiveness of tailored flower strips in reducing pests and crop plant damage

“…However, high parasitism does not necessarily translate into reductions of pest densities or crop damage [28]. Indeed, only few studies found decreased pest levels or reduced crop damage in adjacent crops [17,28,48]. Conservation biocontrol measures are far from universally successful.…”

“…Conservation biocontrol measures are far from universally successful. No effects, or even increasing levels of crop pests and/or damage close to flower strips, have been reported for other study systems [17,49]. These can arise, for example, if pests benefit similarly or even more strongly from the offered resources than their enemies [28,50] or from increased top-down control of pest's natural enemies through (hyper-)parasitoids and predators [21,51].…”

Selective enhancement of parasitoids of rice Lepidoptera pests by sesame (Sesamum indicum) flowers

“…There is a large amount of evidence for increased parasitoid abundance and parasitism levels when flowering plants are present (Balzan and Wäckers 2013;Berndt et al 2006;Díaz et al 2012;Ellis et al 2005;Lavandero et al 2005;Masetti et al 2010;Orre Gordon et al 2013;Segoli and Rosenheim 2013;Simpson et al 2011;Tylianakis et al 2004;Zhu et al 2013a). Potentially, however, floral resources can also have the unwanted effect of providing herbivorous insect pests with nutrients and increasing their performance (Baggen and Gurr 1998;Baggen et al 1999;Balzan and Wäckers 2013;Lavandero et al 2006;Romeis and Wäckers 2002;Wäckers et al 2007;Winkler et al 2010). This risk requires that the selection of plants for use in ecological engineering involves the investigation of the nutritional requirements and resource utilization of both pest species and their natural enemies.…”

The Diversity of Arthropods Predator on Wild Plant of Rice Field with and without Pesticides

“…Habitat for natural enemies are not only the main crop, but also weeds found around the agroecosystems (Meidalima, 2013). Weeds around the plants act as a provider of food (nectar, honey dew and pollen) for arthropod predators (Rusch et al, 2012, Winkler et al, 2010Belz et al, 2013). In addition, weeds around the agroecosystem can serve as a shelter from natural enemies when conditions are not suitable (van Emden, 1991).…”