Landscape simplification reduces classical biological control and crop yield

Abstract

Agricultural intensification resulting in the simplification of agricultural landscapes is known to negatively impact the delivery of key ecosystem services such as the biological control of crop pests. Both conservation and classical biological control may be influenced by the landscape context in which they are deployed; yet studies examining the role of landscape structure in the establishment and success of introduced natural enemies and their interactions with native communities are lacking. In this study, we investigated the relationship between landscape simplification, classical and conservation biological control services and importantly, the outcome of these interactions for crop yield. We showed that agricultural simplification at the landscape scale is associated with an overall reduction in parasitism rates of crop pests. Additionally, only introduced parasitoids were identified, and no native parasitoids were found in crop habitat, irrespective of agricultural landscape simplification. Pest densities in the crop were lower in landscapes with greater proportions of semi-natural habitats. Furthermore, farms with less semi-natural cover in the landscape and consequently, higher pest numbers, had lower yields than farms in less agriculturally dominated landscapes. Our study demonstrates the importance of landscape scale agricultural simplification in mediating the success of biological control programs and highlights the potential risks to native natural enemies in classical biological control programs against native insects. Our results represent an important contribution to an understanding of the landscape-mediated impacts on crop yield that will be essential to implementing effective policies that simultaneously conserve biodiversity and ecosystem services.

Laboratory and field tests of predation on the cereal leaf beetle, Oulema melanopus (Coleoptera: Chrysomelidae)

“…In the year with lower CLB abundance (2015), I observed a significant increase of parasitism associated with an increased proportion of major host crops at multiple scales. Contrary to our finding, Grab et al (2018) reported negative associations between the proportion of crops and tarnished plant bug parasitism by the introduced parasitoid Peristenus digoneutis Loan (Hymenoptera: Braconidae). The same authors concluded that the higher proportion of seminatural habitat in the surrounding landscape was a key factor for explaining tarnished plant bug parasitism.…”

“…Plecas et al (2014) found a positive association between landscape complexity and aphid parasitism in two out of four years of their study, suggesting temporal variation in the response of parasitoid to the landscape complexity. Similarly, Grab et al (2018) found lower tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae) parasitism by Peristenus wasps (Hymenoptera: Braconidae) in strawberry fields within simple landscapes dominated by agricultural fields (e.g., landscapes with low proportion of semi-natural area), suggesting that semi-natural habitats may provide parasitoids with important resources (nectar) that elevate their levels of parasitism. Zaller et al (2009) reported that higher crop abundance, pollen beetle abundance, and length of the roadside ditch were positively associated with rape pollen beetle parasitism at the 250 m spatial scale, suggesting that local scale complexity is important in explaining herbivore abundance in oilseed rape fields.…”

“…Landscape simplification and increased agricultural intensity reduce semi-natural habitats and increase disturbance, and has been associated with declines in pest control services (Grab et al, 2018;Rusch et al, 2016). However, recent work suggests a less clear association between landscape complexity and herbivore suppression.…”

“…Several studies have reported indirect effects of landscape complexity on herbivores through its effects on natural enemies (Bianchi et al, 2006;Chaplin-Kramer et al, 2011). Thies et al (2003 reported positive associations between the proportion of semi-natural area at 1 to 2 km spatial scales and pollen beetle parasitism, and Grab et al (2018) found a high rate of tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae) parasitism in strawberry fields within landscapes with a high proportion of semi-natural habitats at the 0.5 km spatial scale. Other studies, however, have reported that parasitoid responses to landscape complexity are species-specific.…”

Landscape drivers and effectiveness of pest control by insectivorous birds in a landscape-dominant woody crop

“…Agricultural intensification is often characterized by monocultures that spread over extensive areas, creating highly homogeneous landscapes (He et al, 2019). Monocultures that dominate vast areas are especially prone to suffer from pest damage (He et al, 2019; Redlich, Martin, & Steffan-Dewenter, 2018), because spatial and biotic homogenization favors the spread and success of specialist pests and also removes natural habitats that host potential natural enemies (Grab, Danforth, Poveda, & Loeb, 2018; Rusch et al, 2016). In this sense, only natural enemies that tolerate the micro-environmental conditions of the culture, or that span/forage in large areas, can be effective pest control agents in landscape-dominant cultures.…”