The contribution of semi‐natural habitats to biological control is dependent on sentinel prey type

Abstract

1. It is widely recognized that landscape factors affect the biological control of weed seeds and insect pests in arable crops, but landscape effects have been found to be inconsistent between studies.2. Here, we compare six different types of sentinels (surrogate prey that was either live insects or seeds) to measure the effects of semi-natural habitats at field to landscape scales on levels of biological control in winter wheat in the UK. Sentinels were located in fields adjacent to three boundary types: grassy margin, hedgerows or woodland to study the local scale effects and in landscapes of varying heterogeneity in study areas of 1-km radius.3. Overall, mean levels of predation were higher for most insect prey (60.8%) located on the ground compared to the crop (12.2%) and was lower for seeds (5.8%).Predation of sentinels on the ground was attributed to generalist predators.Semi-natural habitats had both positive and negative effects at field and landscape scales, but the response varied with the sentinel type. Herbaceous linear semi-natural habitats had positive effects at local scales for Calliphora vomitoria and Sitobion avenae sentinels and provide evidence that farmers can introduce linear herbaceous features to benefit biological control. In contrast, our distanceweighted kernel models identified a positive relationship between woody habitats and the predation of C. vomitoria and Chenopodium album. Natural aphid infestations were lower in landscapes with more semi-natural habitat. Synthesis and applications. Sentinels may be sensitive enough to detect variationin levels of biological control influenced by semi-natural habitats, but this study confirms that landscape effects differ for different types of sentinel prey. This implies that it may not be possible to categorize landscapes as pest suppressive using a single sentinel type. Future studies should therefore consider using multiple sentinels to give a better perspective on predation intensity. The resulting recommendations for farm management include planting woodland adjacent wheat fields infested with seed predators and positioning herbaceous linear habitats adjacent wheat fields infested with Sitobion avenae, particularly if fields are bordered by woody liner habitats due to their association with decreased S. avenae predation. Additional supporting information may be found online in the Supporting Information section. How to cite this article: McHugh NM, Moreby S, Lof ME, Van der Werf W, Holland JM. The contribution of semi-natural habitats to biological control is dependent on sentinel prey type.

Insect and insecticides in agricultural landscapes; socio-ecological challenges and patterns

“…Inconsistent effects of woody natural habitats on predation and parasitism have been reported previously (Karp et al, 2018). McHugh et al (2020) found that herbaceous habitat was positively associated with predation of aphids, while woody linear habitat was negatively associated with predation of aphids. There are also studies reporting positive associations between biocontrol rates and woody elements in the landscape (Bianchi et al, 2005;Bianchi, Goedhart and Baveco, 2008;Dainese et al, 2017;Dover, 2019).…”

“…However, to mimic natural conditions as much as possible I used one-day old eggs in my set-up, which emit stronger chemical cues than older eggs (Colazza et al, 2010). Fourth, identifying the natural enemies responsible for biocontrol is essential to make strong conclusions on biocontrol potential in any landscape, and to be able to target pest management at specific taxa (Zou et al, 2017;McHugh et al, 2020). However, direct observations to identify natural enemies responsible for predation or parasitism is laborious, time-consuming and difficult to conduct at six to eight sites at the same time (Zou et al, 2017).…”

“…Finally, the generalization of the biocontrol potential in the landscape from predation and parasitism rates of M. brassicae eggs must be done with care, as the enemies of M. brassicae may not be effective against another pests. Habitats that favour a particular natural enemy may not be utilized by other natural enemies, and therefore landscape effects could be specific for the sentinel prey type that was used (McHugh et al, 2020). Still, given that important natural enemy groups of M. brassicae, including staphylinids, ladybeetles, lacewings, and spiders, which were found using sweepnet and yellow sticky trap sampling (Bakker, van der Werf and Bianchi, 2020), it could be argued that using this sentinel system I did get a good indication of biocontrol potential in each landscape.…”

“…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 margins have received little attention.…”

Approaches to Identify the Value of Seminatural Habitats for Conservation Biological Control

“…In the next main stage of the process, the actual level of ecosystem service was measured. For pest control, this entailed developing and deploying a range of sentinel prey items designed to represent either invertebrate pests or weed seeds [41]. Studies were conducted in six economically important cropping systems: oilseed rape (two case studies), pumpkin (one case study), pear (one case study), olive (one case study), winter wheat (two case studies), and vine (one case study) that varied in farming intensity.…”